This document summarizes findings from imaging and thermal analysis of asteroid Bennu by NASA's OSIRIS-REx spacecraft. It finds that Bennu's surface is globally rough, dense with boulders over 1 meter in size, and has a low albedo of 4.4%. Thermal data indicates a moderate global thermal inertia of 350 J m-2 K-1 s-1/2, suggesting surface particle sizes of 0.5-5 cm by simple models, however images show the surface is dominated by boulders over 1 meter. Over 80% of the surface was analyzed, finding a power law distribution of boulder sizes with an index of -2.9 for boulders 8 meters
The unexpected surface of asteroid (101955) BennuSérgio Sacani
Bennu's surface was found to be more diverse and rugged than expected based on pre-encounter data. While its global properties like composition, shape and density matched predictions, high-resolution images revealed an unexpectedly wide range of albedos across its surface as well as many more large boulders than anticipated. This poses challenges for selecting a safe sample site. Magnetite detected on darker regions may indicate fresher material from aqueous alteration. More data is needed to understand Bennu's surface evolution and guide sample acquisition.
The operational environment and rotational acceleration of asteroid (101955) ...Sérgio Sacani
During its approach to asteroid (101955) Bennu, NASA’s Origins, Spectral Interpretation,
Resource Identification, and Security-Regolith Explorer (OSIRIS-REx) spacecraft surveyed
Bennu’s immediate environment, photometric properties, and rotation state. Discovery of
a dusty environment, a natural satellite, or unexpected asteroid characteristics would have
had consequences for the mission’s safety and observation strategy. Here we show that
spacecraft observations during this period were highly sensitive to satellites (sub-meter
scale) but reveal none, although later navigational images indicate that further investigation is
needed. We constrain average dust production in September 2018 from Bennu’s surface
to an upper limit of 150 g s–1 averaged over 34 min. Bennu’s disk-integrated photometric
phase function validates measurements from the pre-encounter astronomical campaign.
We demonstrate that Bennu’s rotation rate is accelerating continuously at 3.63 ± 0.52 × 10–6
degrees day–2, likely due to the Yarkovsky–O’Keefe–Radzievskii–Paddack (YORP) effect, with
evolutionary implications.
Shape of (101955) Bennu indicative of a rubble pile with internal stiffnessSérgio Sacani
The document describes new findings about the asteroid Bennu based on images from the OSIRIS-REx spacecraft. It finds that Bennu has a top-like shape with considerable macroporosity and prominent boulders, suggesting it is a rubble pile. However, it also has high-standing ridges and surface features indicating some level of internal stiffness. The shape and features suggest Bennu formed by reaccumulation and past fast spin, but now its interior allows surface cracking and mass wasting. Key parameters of Bennu such as size, volume, density are consistent with prior estimates from Earth-based radar.
Craters, boulders and regolith of (101955) Bennu indicative of an old and dyn...Sérgio Sacani
- NASA's OSIRIS-REx mission arrived at the near-Earth asteroid Bennu in December 2018 and obtained images revealing its shape and surface features.
- Bennu has a diameter of 492 meters and is classified as a rubble pile asteroid, consisting of loosely bound fragments with high porosity.
- Images show numerous large boulders on Bennu's surface, some over 50 meters in size, indicating impacts in its past. Fractured boulders and impact breccias further suggest a dynamic history.
- The surface shows signs of both ancient features from the main asteroid belt as well as more recent mass movement, with clusters of boulders in low areas and incomplete crater
The GRAIL spacecraft measured the gravity field of the Moon at high resolution, allowing determination of the bulk density and porosity of the lunar crust. The analysis found:
1) The bulk density of the lunar highlands crust is 2550 kg/m3, substantially lower than previous estimates due to impact-induced porosity.
2) The average porosity of the crust is 12%, varying regionally from 4-21% and correlated with impact basins.
3) A new global crustal thickness model was constructed satisfying seismic constraints with an average thickness of 34-43 km, indicating the Moon's composition is not highly enriched compared to Earth.
Evidence for widespread hydrated minerals on asteroid (101955) BennuSérgio Sacani
Early spectral data from the Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer (OSIRISREx) mission reveal evidence for abundant hydrated minerals on the surface of near-Earth asteroid (101955) Bennu in the
form of a near-infrared absorption near 2.7 µm and thermal infrared spectral features that are most similar to those of aqueously altered CM-type carbonaceous chondrites. We observe these spectral features across the surface of Bennu, and there
is no evidence of substantial rotational variability at the spatial scales of tens to hundreds of metres observed to date. In the
visible and near-infrared (0.4 to 2.4 µm) Bennu’s spectrum appears featureless and with a blue (negative) slope, confirming
previous ground-based observations. Bennu may represent a class of objects that could have brought volatiles and organic
chemistry to Earth.
Magnetic field and_wind_of_kappa_ceti_towards_the_planetary_habitability_of_t...Sérgio Sacani
We report magnetic field measurements for κ
1 Cet, a proxy of the young Sun when life arose on Earth. We carry out an analysis
of the magnetic properties determined from spectropolarimetric observations and reconstruct its large-scale surface magnetic
field to derive the magnetic environment, stellar winds and particle flux permeating the interplanetary medium around κ
1 Cet.
Our results show a closer magnetosphere and mass-loss rate of M˙ = 9.7 × 10−13 M yr−1
, i.e., a factor 50 times larger than the
current solar wind mass-loss rate, resulting in a larger interaction via space weather disturbances between the stellar wind and
a hypothetical young-Earth analogue, potentially affecting the planet’s habitability. Interaction of the wind from the young Sun
with the planetary ancient magnetic field may have affected the young Earth and its life conditions.
High precision abundances_of_the_old_solar_twin_insights_on_li_depletion_from...Sérgio Sacani
- The document presents the results of a chemical abundance analysis of the old solar twin star HIP 102152 (8.2 Gyr) and the younger solar twin 18 Sco (2.9 Gyr) using high-resolution UVES spectra.
- Abundances of 21 elements were derived for HIP 102152 with precisions up to 0.004 dex relative to the Sun. The metallicity of HIP 102152 was found to be nearly solar at [Fe/H] = -0.013.
- Elemental abundances as a function of condensation temperature reveal a solar abundance pattern for HIP 102152, unlike most solar twins. Its pattern most closely matches the Sun. The Li abundance
The unexpected surface of asteroid (101955) BennuSérgio Sacani
Bennu's surface was found to be more diverse and rugged than expected based on pre-encounter data. While its global properties like composition, shape and density matched predictions, high-resolution images revealed an unexpectedly wide range of albedos across its surface as well as many more large boulders than anticipated. This poses challenges for selecting a safe sample site. Magnetite detected on darker regions may indicate fresher material from aqueous alteration. More data is needed to understand Bennu's surface evolution and guide sample acquisition.
The operational environment and rotational acceleration of asteroid (101955) ...Sérgio Sacani
During its approach to asteroid (101955) Bennu, NASA’s Origins, Spectral Interpretation,
Resource Identification, and Security-Regolith Explorer (OSIRIS-REx) spacecraft surveyed
Bennu’s immediate environment, photometric properties, and rotation state. Discovery of
a dusty environment, a natural satellite, or unexpected asteroid characteristics would have
had consequences for the mission’s safety and observation strategy. Here we show that
spacecraft observations during this period were highly sensitive to satellites (sub-meter
scale) but reveal none, although later navigational images indicate that further investigation is
needed. We constrain average dust production in September 2018 from Bennu’s surface
to an upper limit of 150 g s–1 averaged over 34 min. Bennu’s disk-integrated photometric
phase function validates measurements from the pre-encounter astronomical campaign.
We demonstrate that Bennu’s rotation rate is accelerating continuously at 3.63 ± 0.52 × 10–6
degrees day–2, likely due to the Yarkovsky–O’Keefe–Radzievskii–Paddack (YORP) effect, with
evolutionary implications.
Shape of (101955) Bennu indicative of a rubble pile with internal stiffnessSérgio Sacani
The document describes new findings about the asteroid Bennu based on images from the OSIRIS-REx spacecraft. It finds that Bennu has a top-like shape with considerable macroporosity and prominent boulders, suggesting it is a rubble pile. However, it also has high-standing ridges and surface features indicating some level of internal stiffness. The shape and features suggest Bennu formed by reaccumulation and past fast spin, but now its interior allows surface cracking and mass wasting. Key parameters of Bennu such as size, volume, density are consistent with prior estimates from Earth-based radar.
Craters, boulders and regolith of (101955) Bennu indicative of an old and dyn...Sérgio Sacani
- NASA's OSIRIS-REx mission arrived at the near-Earth asteroid Bennu in December 2018 and obtained images revealing its shape and surface features.
- Bennu has a diameter of 492 meters and is classified as a rubble pile asteroid, consisting of loosely bound fragments with high porosity.
- Images show numerous large boulders on Bennu's surface, some over 50 meters in size, indicating impacts in its past. Fractured boulders and impact breccias further suggest a dynamic history.
- The surface shows signs of both ancient features from the main asteroid belt as well as more recent mass movement, with clusters of boulders in low areas and incomplete crater
The GRAIL spacecraft measured the gravity field of the Moon at high resolution, allowing determination of the bulk density and porosity of the lunar crust. The analysis found:
1) The bulk density of the lunar highlands crust is 2550 kg/m3, substantially lower than previous estimates due to impact-induced porosity.
2) The average porosity of the crust is 12%, varying regionally from 4-21% and correlated with impact basins.
3) A new global crustal thickness model was constructed satisfying seismic constraints with an average thickness of 34-43 km, indicating the Moon's composition is not highly enriched compared to Earth.
Evidence for widespread hydrated minerals on asteroid (101955) BennuSérgio Sacani
Early spectral data from the Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer (OSIRISREx) mission reveal evidence for abundant hydrated minerals on the surface of near-Earth asteroid (101955) Bennu in the
form of a near-infrared absorption near 2.7 µm and thermal infrared spectral features that are most similar to those of aqueously altered CM-type carbonaceous chondrites. We observe these spectral features across the surface of Bennu, and there
is no evidence of substantial rotational variability at the spatial scales of tens to hundreds of metres observed to date. In the
visible and near-infrared (0.4 to 2.4 µm) Bennu’s spectrum appears featureless and with a blue (negative) slope, confirming
previous ground-based observations. Bennu may represent a class of objects that could have brought volatiles and organic
chemistry to Earth.
Magnetic field and_wind_of_kappa_ceti_towards_the_planetary_habitability_of_t...Sérgio Sacani
We report magnetic field measurements for κ
1 Cet, a proxy of the young Sun when life arose on Earth. We carry out an analysis
of the magnetic properties determined from spectropolarimetric observations and reconstruct its large-scale surface magnetic
field to derive the magnetic environment, stellar winds and particle flux permeating the interplanetary medium around κ
1 Cet.
Our results show a closer magnetosphere and mass-loss rate of M˙ = 9.7 × 10−13 M yr−1
, i.e., a factor 50 times larger than the
current solar wind mass-loss rate, resulting in a larger interaction via space weather disturbances between the stellar wind and
a hypothetical young-Earth analogue, potentially affecting the planet’s habitability. Interaction of the wind from the young Sun
with the planetary ancient magnetic field may have affected the young Earth and its life conditions.
High precision abundances_of_the_old_solar_twin_insights_on_li_depletion_from...Sérgio Sacani
- The document presents the results of a chemical abundance analysis of the old solar twin star HIP 102152 (8.2 Gyr) and the younger solar twin 18 Sco (2.9 Gyr) using high-resolution UVES spectra.
- Abundances of 21 elements were derived for HIP 102152 with precisions up to 0.004 dex relative to the Sun. The metallicity of HIP 102152 was found to be nearly solar at [Fe/H] = -0.013.
- Elemental abundances as a function of condensation temperature reveal a solar abundance pattern for HIP 102152, unlike most solar twins. Its pattern most closely matches the Sun. The Li abundance
The proposed VELOCITÉ mission aims to study geological activity and interior structure on Venus through a combination of orbital and lander-based instruments over a 5-year period. The orbital component, called VISAGE, would carry an interferometric synthetic aperture radar, ground penetrating radar, and high-precision gravity instruments to characterize surface topography, subsurface structure, and gravity field variations. Two landers, called LOVE 1 & 2, would conduct in-situ seismic and permittivity measurements to study near-surface structure. The mission aims to improve understanding of Venusian tectonics, volcanism, and interior dynamics.
Neowise observations of near earth objects- preliminary resultsSérgio Sacani
The NEOWISE survey observed near-Earth objects at infrared wavelengths, detecting over 130 new NEOs. Analysis of the 428 NEOs detected allows estimates of the total NEO population between 100m and 1km in size. The survey found an estimated 981±19 NEOs larger than 1km have been detected, meeting the Spaceguard goal of detecting 90% of objects this size. It also estimates 20,500±3000 NEOs larger than 100m. The cumulative size distribution is best represented by a broken power law.
Earth is the third planet from the Sun, with an average diameter of about 7,918 miles. It has one moon and rotates around its tilted axis once every 24 hours. Earth is unique among the planets in that its name does not come from mythology but from old English. Various instruments like satellites, sonar, and airborne sensors have helped map and monitor Earth's climate, geology, water, and life over time.
Topography of northern_hemisphere_of_mercury_from_messenger_altimeterSérgio Sacani
The document describes a study that used laser altimetry from the MESSENGER spacecraft to create a topographic model of Mercury's northern hemisphere. The study found that Mercury has a much smaller range of elevations compared to Mars or the Moon, likely due to Mercury's higher density and gravitational acceleration smoothing out topographic features. The model revealed numerous large impact structures that influence the shape of the hemisphere but do not significantly affect the distribution of elevations.
Color and albedo_heterogeneity_on_vestaSérgio Sacani
The document summarizes findings from the Dawn spacecraft about the composition and geology of Vesta. It found that Vesta's surface has significant heterogeneity in color and albedo. Spectroscopic data revealed variations in the mineralogy and composition, with the Oppia region showing differences possibly related to mass movements. Craters exposed layers with different mineral and chemical compositions, providing insights into Vesta's complex, stratified crust formed from magmatic processes during planetary differentiation.
Geophysics is the study of the Earth, including its composition and structure, tectonic plates, earthquakes, and natural hazards. A geophysicist conducts seismic surveys using energy sources and geophones to collect and interpret data on subsurface structures. They use computer technology to process and visualize seismic data to find oil, gas, water, and other resources. Geophysics students gain experience through field trips and field schools. Geophysicists and technologists are employed by the petroleum industry, engineering companies, mining companies, universities, and governments.
The document summarizes findings from studying asteroid 4 Vesta using data from NASA's Dawn spacecraft. It finds that Vesta has experienced a violent collisional history, with large impacts creating steep slopes and resurfacing much of the surface. While no unambiguous volcanic deposits were found, some dark material in impact craters may be from excavated subsurface volcanic features. Smooth ponds found on Vesta are also seen on asteroid Eros and are thought to form from impact ejecta collecting in depressions.
The surface of Pluto is more geologically diverse and dynamic than had been expected,
but the role of its tenuous atmosphere in shaping the landscape remains unclear. We
describe observations from the New Horizons spacecraft of regularly spaced, linear ridges
whose morphology, distribution, and orientation are consistent with being transverse
dunes. These are located close to mountainous regions and are orthogonal to nearby wind
streaks. We demonstrate that the wavelength of the dunes (~0.4 to 1 kilometer) is best
explained by the deposition of sand-sized (~200 to ~300 micrometer) particles of methane
ice in moderate winds (<10 meters per second). The undisturbed morphology of the dunes,
and relationships with the underlying convective glacial ice, imply that the dunes have
formed in the very recent geological past.
Geophysical surveys use physical methods at the Earth's surface to measure subsurface physical properties and anomalies. Types of geophysical surveys include gravity, magnetic, electrical, seismic, radiometric, and geothermal methods. The gravity method measures minute variations in gravity caused by differences in subsurface density and distance from the Earth's center. Gravity surveys can be aerial or land-based, using a highly sensitive gravimeter. Processed gravity data is plotted on maps showing variations due to subsurface densities, and is used for hydrocarbon exploration, mineral deposits, cavity detection, and other applications.
This document describes a Bayesian inversion approach to jointly interpret multiple seismic data types that provide information about anisotropic layering in the upper mantle. Surface wave dispersion curves, SKS splitting measurements, and receiver functions are traditionally interpreted separately, but sample different volumes of the Earth and have different sensitivities and uncertainties. The proposed method directly inverts seismograms for SKS and P phases using a cross-convolution approach, avoiding intermediate processing steps. A transdimensional Markov chain Monte Carlo scheme obtains probabilistic 1-D seismic velocity profiles down to 350 km depth beneath two stations, treating the number of layers and presence of anisotropy as unknown parameters. For both stations, the lithosphere-asthenosphere boundary is clearly visible and marked by
Artigo mostra resultados obtidos com o OSIRIS que mostra manchas brilhantes na superfície do cometa 67P/Churyumov-Gerasimenko, interpretadas como sendo gelo de água e provadas via experimentos de laboratório.
Ancient igneous intrusions_and_early_expansion_of_the_moon_revealed_by_grailSérgio Sacani
1) Application of gravity gradiometry to data from the GRAIL mission revealed numerous linear gravity anomalies on the Moon with lengths of hundreds of kilometers.
2) Inversion of the anomalies indicates they are dense vertical intrusions or dikes formed by ancient magmatism during extension of the lunar lithosphere before the end of heavy bombardment.
3) The distribution, orientation, and size of the intrusions suggest they formed as the Moon's radius increased by 0.6-4.9 km early in its history, consistent with predictions of thermal evolution models.
M6.0 2004 Parkfield Earthquake : Seismic AttenuationAli Osman Öncel
HRSN isimli kuyu içi sismik istasyonlar kullanılarak, San Andreas fayı boyunca meydana gelen büyük depremler öncesi sismik azalımın varlığının olup olmadığı araştırılıyor.
This document proposes a new method for rapidly assessing the age of geological units on Mars using measurements of topographic roughness. It hypothesizes that roughness will be correlated with age derived from crater size-frequency distributions, as craters increase surface roughness over time. To test this, the author analyzes topography images and measures roughness from 125 sites across Mars. Age is calculated from crater counts and compared to roughness measurements. Preliminary results show a significant relationship between some roughness measures and age, though there is also variation likely due to crater degradation processes altering roughness without affecting size distributions. If validated, roughness could provide a faster way to assess relative Martian surface ages than traditional crater counting.
Landslide Investigation of Ikwette, Obudu Local Government Area of Cross Rive...iosrjce
This study investigates the causes of a slope failure at Ikwette, Obudu local Government Area of
Cross River State, Nigeria in 2013. It also involves a slope stability analysis of the failed slope, which was OB1.
To understand instability in the study area, a combination of field, geotechnical and statistical analysis were
undertaken. Some obtained parameters were then applied in a slope/W Geostudio 2012 software program which
uses the conventional limit equilibrium methods to simulate the dominant factors inducing instability. Results of
the geotechnical investigations of the samples taken from Ikwette, showed an average maximum dry density
value of 1.63kg/m3
, which was a low to moderate value and average optimum moisture content value of 18%.
Analysis from the particle size distribution, showed that the particle sizes where silty sand, with a Coefficient of
uniformity (Cu) value of 1.8 and Coefficient of curvature (Cc) value of 0.968, indicating that the soil is
uniformly or poorly graded. Triaxial compression test showed an angle of internal friction and cohesion values
averaging around 12.65° and 43kPa respectively, which indicates that the shear strength of the soil was
reduced, due to the activities of high precipitation intensity which increased to a monthly value of 375.3mm
before the landslide event. Also, the factor of safety value for the slope in OB1, where the landslide occurred
was 1.114, which is close to the value for an incipient failure. Hence the results of the aforementioned methods
and simulation shown can be used in predicting areas of possible landslides, as well as the causes of such soil
deformations, and as such, safety measures could be taken against the reoccurrence of landslides in such areas.
This document discusses reservoir geophysics and geology. It begins with an introduction to geophysics, noting that most rocks are opaque so geophysics uses physics to obtain "geophysical images" of the subsurface based on properties like density, magnetism, conductivity, and velocity. It discusses using natural fields like gravity and magnetics to measure subsurface variations at a regional scale. Later sections discuss seismic reflection methods, potential field applications in mapping geology, and benefits of 3D seismic over 2D in providing better geological models. The document provides an overview of key concepts in reservoir geophysics and geology.
Large heterogeneities in_comet_67_p_as_revealed_by_active_pits_from_sinkhole_...Sérgio Sacani
Em um estudo publicado online na edição da revista Nature, 18 cavidades quase circulares foram identificadas no hemisfério norte do cometa 67P/Churyumov-Gerasimenko. As cavidades tem de dezenas a centenas de metros de diâmetro e se estendem a mais de 210 metros abaixo da superfície do cometa. Essas cavidades são ativas e provavelmente criadas por um processo de sumidouro, possivelmente acompanhado por explosões.
A sonda Rosetta da ESA tem monitorado a atividade do cometa por mais de um ano, observando como seu halo de poeira e gás cresce à medida que o cometa se move para perto do Sol ao longo de sua órbita.
De uma distância de apenas centenas de quilômetros, a sonda observa um intrigante padrão de jatos de poeira sendo emitidos do núcleo enquanto eles são ejetados para o espaço.
Mas agora, graças a imagens de alta resolução da câmera de ângulo restrito da sonda, a Optical Spectroscopic and Infrared Remote Imaging System (OSIRIS), feitas de uma distância entre 10 a 30 km do centro do cometa, alguns desses jatos puderam ser rastreados de volta à superfície do cometa, chegando até a sua fonte, é a primeira vez que isso é feito e observado.
The document summarizes findings from the Microwave Instrument on the Rosetta Orbiter (MIRO) regarding the subsurface properties and early activity of comet 67P/Churyumov-Gerasimenko. Key points:
- MIRO detected water vapor emissions from the comet beginning in early June 2014 and measured the total water production rate, which varied from 0.3 kg/s to 1.2 kg/s between June and August.
- Water outgassing displayed periodic variations correlated with the comet's 12.4-hour rotation period and seemed to originate primarily from the comet's "neck" region.
- Subsurface temperatures measured by MIRO showed seasonal and diurnal variations, indicating radiation
Two super-Earths at the edge of the habitable zone of the nearby M dwarf TOI-...Sérgio Sacani
The main scientific goal of TESS is to find planets smaller than Neptune around stars bright enough to allow further characterization studies. Given
our current instrumentation and detection biases, M dwarfs are prime targets to search for small planets that are in (or nearby) the habitable zone
of their host star. Here we use photometric observations and CARMENES radial velocity measurements to validate a pair of transiting planet
candidates found by TESS. The data was fitted simultaneously using a Bayesian MCMC procedure taking into account the stellar variability
present in the photometric and spectroscopic time series. We confirm the planetary origin of the two transiting candidates orbiting around TOI-
2095 (TIC 235678745). The star is a nearby M dwarf (d = 41:90 0:03 pc, Te = 3759 87 K, V = 12:6 mag) with a stellar mass and radius
of M? = 0:44 0:02 M and R? = 0:44 0:02 R, respectively. The planetary system is composed of two transiting planets: TOI-2095b with an
orbital period of Pb = 17:66484 (7 105) days and TOI-2095c with Pc = 28:17232 (14 105) days. Both planets have similar sizes with
Rb = 1:250:07 R and Rc = 1:330:08 R for planet b and c, respectively.We put upper limits on the masses of these objects with Mb < 4:1 M
for the inner and Mc < 7:4 M for the outer planet (95% confidence level). These two planets present equilibrium temperatures in the range of 300
- 350 K and are close to the inner edge of the habitable zone of their star.
Spectroscopy and thermal modelling of the first interstellar object 1I/2017 U...Sérgio Sacani
During the formation and evolution of the Solar System, significant
numbers of cometary and asteroidal bodies were
ejected into interstellar space1,2. It is reasonable to expect that
the same happened for planetary systems other than our own.
Detection of such interstellar objects would allow us to probe
the planetesimal formation processes around other stars, possibly
together with the effects of long-term exposure to the
interstellar medium. 1I/2017 U1 ‘Oumuamua is the first known
interstellar object, discovered by the Pan-STARRS1 telescope
in October 2017 (ref. 3). The discovery epoch photometry
implies a highly elongated body with radii of ~ 200 × 20 m
when a comet-like geometric albedo of 0.04 is assumed. The
observable interstellar object population is expected to be
dominated by comet-like bodies in agreement with our spectra,
yet the reported inactivity of 'Oumuamua implies a lack
of surface ice. Here, we report spectroscopic characterization
of ‘Oumuamua, finding it to be variable with time but similar
to organically rich surfaces found in the outer Solar System.
We show that this is consistent with predictions of an insulating
mantle produced by long-term cosmic ray exposure4.
An internal icy composition cannot therefore be ruled out by
the lack of activity, even though ‘Oumuamua passed within
0.25 au of the Sun.
The proposed VELOCITÉ mission aims to study geological activity and interior structure on Venus through a combination of orbital and lander-based instruments over a 5-year period. The orbital component, called VISAGE, would carry an interferometric synthetic aperture radar, ground penetrating radar, and high-precision gravity instruments to characterize surface topography, subsurface structure, and gravity field variations. Two landers, called LOVE 1 & 2, would conduct in-situ seismic and permittivity measurements to study near-surface structure. The mission aims to improve understanding of Venusian tectonics, volcanism, and interior dynamics.
Neowise observations of near earth objects- preliminary resultsSérgio Sacani
The NEOWISE survey observed near-Earth objects at infrared wavelengths, detecting over 130 new NEOs. Analysis of the 428 NEOs detected allows estimates of the total NEO population between 100m and 1km in size. The survey found an estimated 981±19 NEOs larger than 1km have been detected, meeting the Spaceguard goal of detecting 90% of objects this size. It also estimates 20,500±3000 NEOs larger than 100m. The cumulative size distribution is best represented by a broken power law.
Earth is the third planet from the Sun, with an average diameter of about 7,918 miles. It has one moon and rotates around its tilted axis once every 24 hours. Earth is unique among the planets in that its name does not come from mythology but from old English. Various instruments like satellites, sonar, and airborne sensors have helped map and monitor Earth's climate, geology, water, and life over time.
Topography of northern_hemisphere_of_mercury_from_messenger_altimeterSérgio Sacani
The document describes a study that used laser altimetry from the MESSENGER spacecraft to create a topographic model of Mercury's northern hemisphere. The study found that Mercury has a much smaller range of elevations compared to Mars or the Moon, likely due to Mercury's higher density and gravitational acceleration smoothing out topographic features. The model revealed numerous large impact structures that influence the shape of the hemisphere but do not significantly affect the distribution of elevations.
Color and albedo_heterogeneity_on_vestaSérgio Sacani
The document summarizes findings from the Dawn spacecraft about the composition and geology of Vesta. It found that Vesta's surface has significant heterogeneity in color and albedo. Spectroscopic data revealed variations in the mineralogy and composition, with the Oppia region showing differences possibly related to mass movements. Craters exposed layers with different mineral and chemical compositions, providing insights into Vesta's complex, stratified crust formed from magmatic processes during planetary differentiation.
Geophysics is the study of the Earth, including its composition and structure, tectonic plates, earthquakes, and natural hazards. A geophysicist conducts seismic surveys using energy sources and geophones to collect and interpret data on subsurface structures. They use computer technology to process and visualize seismic data to find oil, gas, water, and other resources. Geophysics students gain experience through field trips and field schools. Geophysicists and technologists are employed by the petroleum industry, engineering companies, mining companies, universities, and governments.
The document summarizes findings from studying asteroid 4 Vesta using data from NASA's Dawn spacecraft. It finds that Vesta has experienced a violent collisional history, with large impacts creating steep slopes and resurfacing much of the surface. While no unambiguous volcanic deposits were found, some dark material in impact craters may be from excavated subsurface volcanic features. Smooth ponds found on Vesta are also seen on asteroid Eros and are thought to form from impact ejecta collecting in depressions.
The surface of Pluto is more geologically diverse and dynamic than had been expected,
but the role of its tenuous atmosphere in shaping the landscape remains unclear. We
describe observations from the New Horizons spacecraft of regularly spaced, linear ridges
whose morphology, distribution, and orientation are consistent with being transverse
dunes. These are located close to mountainous regions and are orthogonal to nearby wind
streaks. We demonstrate that the wavelength of the dunes (~0.4 to 1 kilometer) is best
explained by the deposition of sand-sized (~200 to ~300 micrometer) particles of methane
ice in moderate winds (<10 meters per second). The undisturbed morphology of the dunes,
and relationships with the underlying convective glacial ice, imply that the dunes have
formed in the very recent geological past.
Geophysical surveys use physical methods at the Earth's surface to measure subsurface physical properties and anomalies. Types of geophysical surveys include gravity, magnetic, electrical, seismic, radiometric, and geothermal methods. The gravity method measures minute variations in gravity caused by differences in subsurface density and distance from the Earth's center. Gravity surveys can be aerial or land-based, using a highly sensitive gravimeter. Processed gravity data is plotted on maps showing variations due to subsurface densities, and is used for hydrocarbon exploration, mineral deposits, cavity detection, and other applications.
This document describes a Bayesian inversion approach to jointly interpret multiple seismic data types that provide information about anisotropic layering in the upper mantle. Surface wave dispersion curves, SKS splitting measurements, and receiver functions are traditionally interpreted separately, but sample different volumes of the Earth and have different sensitivities and uncertainties. The proposed method directly inverts seismograms for SKS and P phases using a cross-convolution approach, avoiding intermediate processing steps. A transdimensional Markov chain Monte Carlo scheme obtains probabilistic 1-D seismic velocity profiles down to 350 km depth beneath two stations, treating the number of layers and presence of anisotropy as unknown parameters. For both stations, the lithosphere-asthenosphere boundary is clearly visible and marked by
Artigo mostra resultados obtidos com o OSIRIS que mostra manchas brilhantes na superfície do cometa 67P/Churyumov-Gerasimenko, interpretadas como sendo gelo de água e provadas via experimentos de laboratório.
Ancient igneous intrusions_and_early_expansion_of_the_moon_revealed_by_grailSérgio Sacani
1) Application of gravity gradiometry to data from the GRAIL mission revealed numerous linear gravity anomalies on the Moon with lengths of hundreds of kilometers.
2) Inversion of the anomalies indicates they are dense vertical intrusions or dikes formed by ancient magmatism during extension of the lunar lithosphere before the end of heavy bombardment.
3) The distribution, orientation, and size of the intrusions suggest they formed as the Moon's radius increased by 0.6-4.9 km early in its history, consistent with predictions of thermal evolution models.
M6.0 2004 Parkfield Earthquake : Seismic AttenuationAli Osman Öncel
HRSN isimli kuyu içi sismik istasyonlar kullanılarak, San Andreas fayı boyunca meydana gelen büyük depremler öncesi sismik azalımın varlığının olup olmadığı araştırılıyor.
This document proposes a new method for rapidly assessing the age of geological units on Mars using measurements of topographic roughness. It hypothesizes that roughness will be correlated with age derived from crater size-frequency distributions, as craters increase surface roughness over time. To test this, the author analyzes topography images and measures roughness from 125 sites across Mars. Age is calculated from crater counts and compared to roughness measurements. Preliminary results show a significant relationship between some roughness measures and age, though there is also variation likely due to crater degradation processes altering roughness without affecting size distributions. If validated, roughness could provide a faster way to assess relative Martian surface ages than traditional crater counting.
Landslide Investigation of Ikwette, Obudu Local Government Area of Cross Rive...iosrjce
This study investigates the causes of a slope failure at Ikwette, Obudu local Government Area of
Cross River State, Nigeria in 2013. It also involves a slope stability analysis of the failed slope, which was OB1.
To understand instability in the study area, a combination of field, geotechnical and statistical analysis were
undertaken. Some obtained parameters were then applied in a slope/W Geostudio 2012 software program which
uses the conventional limit equilibrium methods to simulate the dominant factors inducing instability. Results of
the geotechnical investigations of the samples taken from Ikwette, showed an average maximum dry density
value of 1.63kg/m3
, which was a low to moderate value and average optimum moisture content value of 18%.
Analysis from the particle size distribution, showed that the particle sizes where silty sand, with a Coefficient of
uniformity (Cu) value of 1.8 and Coefficient of curvature (Cc) value of 0.968, indicating that the soil is
uniformly or poorly graded. Triaxial compression test showed an angle of internal friction and cohesion values
averaging around 12.65° and 43kPa respectively, which indicates that the shear strength of the soil was
reduced, due to the activities of high precipitation intensity which increased to a monthly value of 375.3mm
before the landslide event. Also, the factor of safety value for the slope in OB1, where the landslide occurred
was 1.114, which is close to the value for an incipient failure. Hence the results of the aforementioned methods
and simulation shown can be used in predicting areas of possible landslides, as well as the causes of such soil
deformations, and as such, safety measures could be taken against the reoccurrence of landslides in such areas.
This document discusses reservoir geophysics and geology. It begins with an introduction to geophysics, noting that most rocks are opaque so geophysics uses physics to obtain "geophysical images" of the subsurface based on properties like density, magnetism, conductivity, and velocity. It discusses using natural fields like gravity and magnetics to measure subsurface variations at a regional scale. Later sections discuss seismic reflection methods, potential field applications in mapping geology, and benefits of 3D seismic over 2D in providing better geological models. The document provides an overview of key concepts in reservoir geophysics and geology.
Large heterogeneities in_comet_67_p_as_revealed_by_active_pits_from_sinkhole_...Sérgio Sacani
Em um estudo publicado online na edição da revista Nature, 18 cavidades quase circulares foram identificadas no hemisfério norte do cometa 67P/Churyumov-Gerasimenko. As cavidades tem de dezenas a centenas de metros de diâmetro e se estendem a mais de 210 metros abaixo da superfície do cometa. Essas cavidades são ativas e provavelmente criadas por um processo de sumidouro, possivelmente acompanhado por explosões.
A sonda Rosetta da ESA tem monitorado a atividade do cometa por mais de um ano, observando como seu halo de poeira e gás cresce à medida que o cometa se move para perto do Sol ao longo de sua órbita.
De uma distância de apenas centenas de quilômetros, a sonda observa um intrigante padrão de jatos de poeira sendo emitidos do núcleo enquanto eles são ejetados para o espaço.
Mas agora, graças a imagens de alta resolução da câmera de ângulo restrito da sonda, a Optical Spectroscopic and Infrared Remote Imaging System (OSIRIS), feitas de uma distância entre 10 a 30 km do centro do cometa, alguns desses jatos puderam ser rastreados de volta à superfície do cometa, chegando até a sua fonte, é a primeira vez que isso é feito e observado.
The document summarizes findings from the Microwave Instrument on the Rosetta Orbiter (MIRO) regarding the subsurface properties and early activity of comet 67P/Churyumov-Gerasimenko. Key points:
- MIRO detected water vapor emissions from the comet beginning in early June 2014 and measured the total water production rate, which varied from 0.3 kg/s to 1.2 kg/s between June and August.
- Water outgassing displayed periodic variations correlated with the comet's 12.4-hour rotation period and seemed to originate primarily from the comet's "neck" region.
- Subsurface temperatures measured by MIRO showed seasonal and diurnal variations, indicating radiation
Two super-Earths at the edge of the habitable zone of the nearby M dwarf TOI-...Sérgio Sacani
The main scientific goal of TESS is to find planets smaller than Neptune around stars bright enough to allow further characterization studies. Given
our current instrumentation and detection biases, M dwarfs are prime targets to search for small planets that are in (or nearby) the habitable zone
of their host star. Here we use photometric observations and CARMENES radial velocity measurements to validate a pair of transiting planet
candidates found by TESS. The data was fitted simultaneously using a Bayesian MCMC procedure taking into account the stellar variability
present in the photometric and spectroscopic time series. We confirm the planetary origin of the two transiting candidates orbiting around TOI-
2095 (TIC 235678745). The star is a nearby M dwarf (d = 41:90 0:03 pc, Te = 3759 87 K, V = 12:6 mag) with a stellar mass and radius
of M? = 0:44 0:02 M and R? = 0:44 0:02 R, respectively. The planetary system is composed of two transiting planets: TOI-2095b with an
orbital period of Pb = 17:66484 (7 105) days and TOI-2095c with Pc = 28:17232 (14 105) days. Both planets have similar sizes with
Rb = 1:250:07 R and Rc = 1:330:08 R for planet b and c, respectively.We put upper limits on the masses of these objects with Mb < 4:1 M
for the inner and Mc < 7:4 M for the outer planet (95% confidence level). These two planets present equilibrium temperatures in the range of 300
- 350 K and are close to the inner edge of the habitable zone of their star.
Spectroscopy and thermal modelling of the first interstellar object 1I/2017 U...Sérgio Sacani
During the formation and evolution of the Solar System, significant
numbers of cometary and asteroidal bodies were
ejected into interstellar space1,2. It is reasonable to expect that
the same happened for planetary systems other than our own.
Detection of such interstellar objects would allow us to probe
the planetesimal formation processes around other stars, possibly
together with the effects of long-term exposure to the
interstellar medium. 1I/2017 U1 ‘Oumuamua is the first known
interstellar object, discovered by the Pan-STARRS1 telescope
in October 2017 (ref. 3). The discovery epoch photometry
implies a highly elongated body with radii of ~ 200 × 20 m
when a comet-like geometric albedo of 0.04 is assumed. The
observable interstellar object population is expected to be
dominated by comet-like bodies in agreement with our spectra,
yet the reported inactivity of 'Oumuamua implies a lack
of surface ice. Here, we report spectroscopic characterization
of ‘Oumuamua, finding it to be variable with time but similar
to organically rich surfaces found in the outer Solar System.
We show that this is consistent with predictions of an insulating
mantle produced by long-term cosmic ray exposure4.
An internal icy composition cannot therefore be ruled out by
the lack of activity, even though ‘Oumuamua passed within
0.25 au of the Sun.
Two temperate Earth-mass planets orbiting the nearby star GJ 1002Sérgio Sacani
We report the discovery and characterisation of two Earth-mass planets orbiting in the habitable zone of the nearby M-dwarf GJ 1002 based on
the analysis of the radial-velocity (RV) time series from the ESPRESSO and CARMENES spectrographs. The host star is the quiet M5.5 V star
GJ 1002 (relatively faint in the optical, V ∼ 13.8 mag, but brighter in the infrared, J ∼ 8.3 mag), located at 4.84 pc from the Sun.
We analyse 139 spectroscopic observations taken between 2017 and 2021. We performed a joint analysis of the time series of the RV and full-width
half maximum (FWHM) of the cross-correlation function (CCF) to model the planetary and stellar signals present in the data, applying Gaussian
process regression to deal with the stellar activity.
We detect the signal of two planets orbiting GJ 1002. GJ 1002 b is a planet with a minimum mass mp sin i of 1.08 ± 0.13 M⊕ with an orbital period
of 10.3465 ± 0.0027 days at a distance of 0.0457 ± 0.0013 au from its parent star, receiving an estimated stellar flux of 0.67 F⊕. GJ 1002 c is a
planet with a minimum mass mp sin i of 1.36 ± 0.17 M⊕ with an orbital period of 20.202 ± 0.013 days at a distance of 0.0738 ± 0.0021 au from
its parent star, receiving an estimated stellar flux of 0.257 F⊕. We also detect the rotation signature of the star, with a period of 126 ± 15 days. We
find that there is a correlation between the temperature of certain optical elements in the spectrographs and changes in the instrumental profile that
can affect the scientific data, showing a seasonal behaviour that creates spurious signals at periods longer than ∼ 200 days.
GJ 1002 is one of the few known nearby systems with planets that could potentially host habitable environments. The closeness of the host star
to the Sun makes the angular sizes of the orbits of both planets (∼ 9.7 mas and ∼ 15.7 mas, respectively) large enough for their atmosphere to be
studied via high-contrast high-resolution spectroscopy with instruments such as the future spectrograph ANDES for the ELT or the LIFE mission.
Two warm Neptunes transiting HIP 9618 revealed by TESS and CheopsSérgio Sacani
This document summarizes the discovery of two warm Neptunes transiting the bright star HIP 9618, as revealed by TESS and CHEOPS observations. TESS observed two transits of one planet (HIP 9618 b), separated by an 11.8 day gap, and one transit of a second planet (HIP 9618 c). Follow-up photometry and reanalysis of the TESS data determined the true period of HIP 9618 b to be 20.77291 days. CHEOPS then performed targeted photometry to determine the true 52.56349 day period of HIP 9618 c. High-resolution spectroscopy found HIP 9618 b has a mass of 10.0 ± 3.
VIMS images of the Huygens landing site on Titan acquired during Cassini flybys in October and December 2004 provide insight into surface features near the landing site with spatial resolutions of 14.4-19 km/pixel. Ratio images of the brightest and darkest spectra in the 2.03 μm window reveal a particularly contrasted structure north of the landing site, consistent with local enrichment in exposed water ice. The images also show a possible 150 km diameter impact crater with a central peak. While scattering from haze particles dominates Titan's spectrum, spectral ratios of bright and dark areas suggest differences in surface composition and/or topography related to DISR images of the site.
The extremely high albedo of LTT 9779 b revealed by CHEOPSSérgio Sacani
Optical secondary eclipse measurements of small planets can provide a wealth of information about the reflective properties
of these worlds, but the measurements are particularly challenging to attain because of their relatively shallow depth. If such signals
can be detected and modeled, however, they can provide planetary albedos, thermal characteristics, and information on absorbers in
the upper atmosphere.
Aims. We aim to detect and characterize the optical secondary eclipse of the planet LTT 9779 b using the CHaracterising ExOPlanet
Satellite (CHEOPS) to measure the planetary albedo and search for the signature of atmospheric condensates.
Methods. We observed ten secondary eclipses of the planet with CHEOPS. We carefully analyzed and detrended the light curves using
three independent methods to perform the final astrophysical detrending and eclipse model fitting of the individual and combined light
curves.
Results. Each of our analysis methods yielded statistically similar results, providing a robust detection of the eclipse of LTT 9779 b
with a depth of 115±24 ppm. This surprisingly large depth provides a geometric albedo for the planet of 0.80+0.10
−0.17, consistent with
estimates of radiative-convective models. This value is similar to that of Venus in our own Solar System. When combining the eclipse
from CHEOPS with the measurements from TESS and Spitzer, our global climate models indicate that LTT 9779 b likely has a super
metal-rich atmosphere, with a lower limit of 400× solar being found, and the presence of silicate clouds. The observations also reveal
hints of optical eclipse depth variability, but these have yet to be confirmed.
Conclusions. The results found here in the optical when combined with those in the near-infrared provide the first steps toward
understanding the atmospheric structure and physical processes of ultrahot Neptune worlds that inhabit the Neptune desert.
A Tale of 3 Dwarf Planets: Ices and Organics on Sedna, Gonggong, and Quaoar f...Sérgio Sacani
The dwarf planets Sedna, Gonggong, and Quaoar are interesting in being somewhat smaller than
the methane-rich bodies of the Kuiper Belt (Pluto, Eris, Makemake), yet large enough to be
spherical and to have possibly undergone interior melting and differentiation. They also reside
on very different orbits, making them an ideal suite of bodies for untangling effects of size and
orbit on present day surface composition. We observed Sedna, Gonggong, and Quaoar with the
NIRSpec instrument on the James Webb Space Telescope (JWST). All three bodies were
observed in the low-resolution prism mode at wavelengths spanning 0.7 to 5.2 μm. Quaoar was
additionally observed at 10x higher spectral resolution from 0.97 to 3.16 μm using mediumresolution gratings. Sedna’s spectrum shows a large number of absorption features due to ethane
(C2H6), as well as acetylene (C2H2), ethylene (C2H4), H2O, and possibly minor CO2.
Gonggong’s spectrum also shows several, but fewer and weaker, ethane features, along with
stronger and cleaner H2O features and CO2 complexed with other molecules. Quaoar’s prism
spectrum shows even fewer and weaker ethane features, the deepest and cleanest H2O features, a
feature at 3.2 μm possibly due to HCN, and CO2 ice. The higher-resolution medium grating
spectrum of Quaoar reveals several overtone and combination bands of ethane and methane
(CH4). Spectra of all three objects show steep red spectral slopes and strong, broad absorptions
between 2.7 and 3.6 μm indicative of complex organic molecules. The suite of light
hydrocarbons and complex organic molecules are interpreted as the products of irradiation of
methane. The differences in apparent abundances of irradiation products among these three
similarly-sized bodies are likely due to their distinctive orbits, which lead to different timescales
of methane retention and to different charged particle irradiation environments. In all cases,
however, the continued presence of light hydrocarbons implies a resupply of methane to the
2
surface. We suggest that these three bodies have undergone internal melting and geochemical
evolution similar to the larger dwarf planets and distinct from all smaller KBOs. The feature
identification presented in this paper is the first step of analysis, and additional insight into the
relative abundances and mixing states of materials on these surfaces will come from future
spectral modeling of these data.
Observation of large scale precursor correlations between cosmic rays and ear...Sérgio Sacani
The search for correlations between secondary cosmic ray detection rates and seismic
effects has long been a subject of investigation motivated by the hope of identifying a new
precursor type that could feed a global early warning system against earthquakes. Here we show
for the first time that the average variation of the cosmic ray detection rates correlates with the
global seismic activity to be observed with a time lag of approximately two weeks, and that the
significance of the effect varies with a periodicity resembling the undecenal solar cycle, with a
shift in phase of around three years, exceeding 6 𝜎 at local maxima. The precursor characteristics
of the observed correlations point to a pioneer perspective of an early warning system against
earthquakes.
First detection of CO2 emission in a Centaur: JWST NIRSpec observations of 39...Sérgio Sacani
Centaurs are minor solar system bodies with orbits transitioning between those of Trans-Neptunian
Scattered Disk objects and Jupiter Family comets. 39P/Oterma is a frequently active Centaur that
has recently held both Centaur and JFC classifications and was observed with the JWST NIRSpec
instrument on 2022 July 27 UTC while it was 5.82 au from the Sun. For the first time, CO2 gas
emission was detected in a Centaur, with a production rate of QCO2 = (5.96 ± 0.80) × 1023 molecules
s
−1
. This is the lowest detection of CO2 of any Centaur or comet. CO and H2O were not detected
down to constraining upper limits. Derived mixing ratios of QCO/QCO2 ≤2.03 and QCO2
/QH2O ≥0.60
are consistent with CO2 and/or CO outgassing playing large roles in driving the activity, but not water,
and show a significant difference between the coma abundances of 29P/Schwassmann-Wachmann 1,
another Centaur at a similar heliocentric distance, which may be explained by thermal processing of
39P’s surface during its previous Jupiter-family comet orbit. To help contextualize the JWST data we
also acquired visible CCD imaging data on two dates in July (Gemini North) and September (Lowell
Discovery Telescope) 2022. Image analysis and photometry based on these data are consistent with a
point source detection and an estimated effective nucleus radius of 39P in the range of Rnuc =2.21 to
2.49 km.
Imaging the Inner Astronomical Unit of the Herbig Be Star HD 190073Sérgio Sacani
The inner regions of protoplanetary disks host many complex physical processes such as star–disk interactions,
magnetic fields, planet formation, and the migration of new planets. To study directly this region requires
milliarcsecond angular resolution, beyond the diffraction limit of the world's largest optical telescopes and even too
small for the millimeter-wave interferometer Atacama Large Millimeter/submillimeter Array (ALMA). However,
we can use infrared interferometers to image the inner astronomical unit. Here, we present new results from the
CHARA and VLTI arrays for the young and luminous Herbig Be star HD 190073. We detect a sub-astronomical
unit (sub-AU) cavity surrounded by a ring-like structure that we interpret as the dust destruction front. We model
the shape with six radial profiles, three symmetric and three asymmetric, and present a model-free image
reconstruction. All the models are consistent with a near face-on disk with an inclination 20°, and we measure an
average ring radius of 1.4 ± 0.2 mas (1.14 au). Around 48% of the total flux comes from the disk with 15% of that
emission appearing to emerge from inside the inner rim. The cause of emission is still unclear, perhaps due to
different dust grain compositions or gas emission. The skewed models and the imaging point to an off-center star,
possibly due to binarity. Our image shows sub-AU structure, which seems to move between the two epochs
inconsistently with Keplerian motion and we discuss possible explanations for this apparent change.
Jupiter’s interior and deep atmosphere: The initial pole-to-pole passes with ...Sérgio Sacani
On 27 August 2016, the Juno spacecraft acquired science observations of Jupiter,
passing less than 5000 kilometers above the equatorial cloud tops. Images of Jupiter’s
poles show a chaotic scene, unlike Saturn’s poles. Microwave sounding reveals weather
features at pressures deeper than 100 bars, dominated by an ammonia-rich, narrow
low-latitude plume resembling a deeper, wider version of Earth’s Hadley cell. Near-infrared
mapping reveals the relative humidity within prominent downwelling regions. Juno’s
measured gravity field differs substantially from the last available estimate and is one
order of magnitude more precise. This has implications for the distribution of heavy
elements in the interior, including the existence and mass of Jupiter’s core. The observed
magnetic field exhibits smaller spatial variations than expected, indicative of a rich
harmonic content.
XUE: Molecular Inventory in the Inner Region of an Extremely Irradiated Proto...Sérgio Sacani
This document presents the first results from the JWST XUE program, which observed 15 protoplanetary disks in the NGC 6357 star-forming region using MIRI. For the disk XUE 1, located near massive stars, the following was found:
1) Abundant water, CO, CO2, HCN, and C2H2 were detected in the inner few AU, indicating an oxygen-dominated gas-phase chemistry similar to isolated disks.
2) Small crystalline silicate dust is present at the disk surface.
3) The column densities and chemistry are surprisingly similar to isolated disks despite the extreme radiation environment, implying inner disks can retain conditions conducive to rocky planet
TEMPORAL EVOLUTION OF THE HIGH-ENERGY IRRADIATION AND WATER CONTENT OF TRAPPI...Sérgio Sacani
The ultracool dwarf star TRAPPIST-1 hosts seven Earth-size transiting planets, some of which could
harbour liquid water on their surfaces. UV observations are essential to measure their high-energy
irradiation, and to search for photodissociated water escaping from their putative atmospheres. Our
new observations of TRAPPIST-1 Ly-α line during the transit of TRAPPIST-1c show an evolution of
the star emission over three months, preventing us from assessing the presence of an extended hydrogen
exosphere. Based on the current knowledge of the stellar irradiation, we investigated the likely history
of water loss in the system. Planets b to d might still be in a runaway phase, and planets within the
orbit of TRAPPIST-1g could have lost more than 20 Earth oceans after 8 Gyr of hydrodynamic escape.
However, TRAPPIST-1e to h might have lost less than 3 Earth oceans if hydrodynamic escape stopped
once they entered the habitable zone. We caution that these estimates remain limited by the large
uncertainty on the planet masses. They likely represent upper limits on the actual water loss because
our assumptions maximize the XUV-driven escape, while photodissociation in the upper atmospheres
should be the limiting process. Late-stage outgassing could also have contributed significant amounts
of water for the outer, more massive planets after they entered the habitable zone. While our results
suggest that the outer planets are the best candidates to search for water with the JWST, they also
highlight the need for theoretical studies and complementary observations in all wavelength domains
to determine the nature of the TRAPPIST-1 planets, and their potential habitability.
Keywords: planetary systems - Stars: individual: TRAPPIST-1
Gliese 12 b, a temperate Earth-sized planet at 12 parsecs discovered with TES...Sérgio Sacani
We report on the discovery of Gliese 12 b, the nearest transiting temperate, Earth-sized planet found to date. Gliese 12 is a
bright (V = 12.6 mag, K = 7.8 mag) metal-poor M4V star only 12.162 ± 0.005 pc away from the Solar system with one of the
lowest stellar activity levels known for M-dwarfs. A planet candidate was detected by TESS based on only 3 transits in sectors
42, 43, and 57, with an ambiguity in the orbital period due to observational gaps. We performed follow-up transit observations
with CHEOPS and ground-based photometry with MINERVA-Australis, SPECULOOS, and Purple Mountain Observatory,
as well as further TESS observations in sector 70. We statistically validate Gliese 12 b as a planet with an orbital period of
12.76144 ± 0.00006 d and a radius of 1.0 ± 0.1 R⊕, resulting in an equilibrium temperature of ∼315 K. Gliese 12 b has excellent
future prospects for precise mass measurement, which may inform how planetary internal structure is affected by the stellar
compositional environment. Gliese 12 b also represents one of the best targets to study whether Earth-like planets orbiting cool
stars can retain their atmospheres, a crucial step to advance our understanding of habitability on Earth and across the galaxy.
Molecular gas clumps_from_the_destruction_of_icy_bodies_in_beta_pictoris_debr...Sérgio Sacani
1) ALMA observations detected carbon monoxide gas orbiting in a debris disk around the young star Beta Pictoris, with a total mass equivalent to 0.0023 times the mass of Earth's Moon.
2) The gas is distributed asymmetrically, with 30% located in a single clump 85 AU from the star. This gas clump is aligned with the orbit of an inner planet in the system.
3) The gas must be continuously replenished, likely from the destruction of icy planetesimals and comets through collisions within the debris disk. The collisions may be enhanced in the gas clump due to resonances with an unseen giant planet or from remnants of a large collision between
Molecular Gas Clumps from the Destruction of Icy Bodies in the β Pictoris Deb...GOASA
1) ALMA observations detected carbon monoxide gas orbiting in a debris disk around the young star Beta Pictoris, with a total mass equivalent to 0.0023 times the mass of Earth's Moon.
2) The gas is distributed asymmetrically, with 30% located in a single clump 85 AU from the star. This gas clump is aligned with the orbit of an inner planet in the system.
3) The gas must be continuously replenished, likely from the destruction of icy planetesimals and comets through collisions within the debris disk. The collisions may be enhanced in the gas clump due to resonances with an unseen giant planet or the remnants of a large collision between
Refined parameters of the HD 22946 planetary system and the true orbital peri...Sérgio Sacani
Multi-planet systems are important sources of information regarding the evolution of planets. However, the long-period
planets in these systems often escape detection. These objects in particular may retain more of their primordial characteristics compared
to close-in counterparts because of their increased distance from the host star. HD 22946 is a bright (G = 8.13 mag) late F-type star
around which three transiting planets were identified via Transiting Exoplanet Survey Satellite (TESS) photometry, but the true orbital
period of the outermost planet d was unknown until now.
Aims. We aim to use the Characterising Exoplanet Satellite (CHEOPS) space telescope to uncover the true orbital period of HD 22946d
and to refine the orbital and planetary properties of the system, especially the radii of the planets.
Methods. We used the available TESS photometry of HD 22946 and observed several transits of the planets b, c, and d using CHEOPS.
We identified two transits of planet d in the TESS photometry, calculated the most probable period aliases based on these data, and
then scheduled CHEOPS observations. The photometric data were supplemented with ESPRESSO (Echelle SPectrograph for Rocky
Exoplanets and Stable Spectroscopic Observations) radial velocity data. Finally, a combined model was fitted to the entire dataset in
order to obtain final planetary and system parameters.
Results. Based on the combined TESS and CHEOPS observations, we successfully determined the true orbital period of the planet d
to be 47.42489 ± 0.00011 days, and derived precise radii of the planets in the system, namely 1.362 ± 0.040 R⊕, 2.328 ± 0.039 R⊕, and
2.607 ± 0.060 R⊕ for planets b, c, and d, respectively. Due to the low number of radial velocities, we were only able to determine 3σ
upper limits for these respective planet masses, which are 13.71 M⊕, 9.72 M⊕, and 26.57 M⊕. We estimated that another 48 ESPRESSO
radial velocities are needed to measure the predicted masses of all planets in HD 22946. We also derived stellar parameters for the host
star.
Conclusions. Planet c around HD 22946 appears to be a promising target for future atmospheric characterisation via transmission
spectroscopy. We can also conclude that planet d, as a warm sub-Neptune, is very interesting because there are only a few similar
confirmed exoplanets to date. Such objects are worth investigating in the near future, for example in terms of their composition and
internal structure.
This document presents an analysis of transit spectroscopy observations of three exoplanets - WASP-12 b, WASP-17 b, and WASP-19 b - using the Wide Field Camera 3 instrument on the Hubble Space Telescope. The observations achieved almost photon-limited precision but uncertainties in the transit depths were increased by the uneven sampling of the light curves. The final transit spectra for all three planets are consistent with the presence of a water absorption feature at 1.4 microns, though the amplitude is smaller than expected from previous Spitzer observations possibly due to hazes. Due to degeneracies between models, the data cannot unambiguously constrain the atmospheric compositions without additional observations.
Exomoons & Exorings with the Habitable Worlds Observatory I: On the Detection...Sérgio Sacani
The highest priority recommendation of the Astro2020 Decadal Survey for space-based astronomy
was the construction of an observatory capable of characterizing habitable worlds. In this paper series
we explore the detectability of and interference from exomoons and exorings serendipitously observed
with the proposed Habitable Worlds Observatory (HWO) as it seeks to characterize exoplanets, starting
in this manuscript with Earth-Moon analog mutual events. Unlike transits, which only occur in systems
viewed near edge-on, shadow (i.e., solar eclipse) and lunar eclipse mutual events occur in almost every
star-planet-moon system. The cadence of these events can vary widely from ∼yearly to multiple events
per day, as was the case in our younger Earth-Moon system. Leveraging previous space-based (EPOXI)
lightcurves of a Moon transit and performance predictions from the LUVOIR-B concept, we derive
the detectability of Moon analogs with HWO. We determine that Earth-Moon analogs are detectable
with observation of ∼2-20 mutual events for systems within 10 pc, and larger moons should remain
detectable out to 20 pc. We explore the extent to which exomoon mutual events can mimic planet
features and weather. We find that HWO wavelength coverage in the near-IR, specifically in the 1.4 µm
water band where large moons can outshine their host planet, will aid in differentiating exomoon signals
from exoplanet variability. Finally, we predict that exomoons formed through collision processes akin
to our Moon are more likely to be detected in younger systems, where shorter orbital periods and
favorable geometry enhance the probability and frequency of mutual events.
EUV fine structure and variability associated with coronal rain revealed by S...Sérgio Sacani
Coronal rain is the most dramatic cooling phenomenon of the solar corona. Recent observations in the visible and UV
spectrum have shown that coronal rain is a pervasive phenomenon in active regions. Its strong link with coronal heating through the
Thermal Non-Equilibrium (TNE) - Thermal Instability (TI) scenario, makes it an essential diagnostic tool for the heating properties.
Another puzzling feature of the solar corona, besides the heating, is its filamentary structure and variability, particularly in the EUV.
Aims. We aim to identify observable features of the TNE-TI scenario underlying coronal rain at small and large spatial scales, to
understand the role it plays in the solar corona.
Methods. We use EUV datasets at unprecedented spatial resolution of ≈ 240 km from the High Resolution Imager (HRI) in the EUV
(HRIEUV) of the Extreme Ultraviolet Imager (EUI) and SPICE on board Solar Orbiter from the spring 2022 perihelion.
Results. EUV absorption features produced by coronal rain are detected at scales as small as 260 km. As the rain falls, heating
and compression is produced immediately downstream, leading to a small EUV brightening accompanying the fall and producing
a ‘fireball’ phenomenon in the solar corona. Just prior to impact, a flash-like EUV brightening downstream of the rain, lasting a
few minutes is observed for the fastest events. For the first time, we detect the atmospheric response to the rain’s impact on the
chromosphere and consists of upward propagating rebound shocks and flows partly reheating the loop. The observed widths of the
rain clumps are 500 ± 200 km. They exhibit a broad velocity distribution of 10 − 150 km s−1
, peaking below 50 km s−1
. Coronal
strands of similar widths are observed along the same loops co-spatial with cool filamentary structure seen with SPICE, which we
interpret as the Condensation Corona Transition Region. Matching with the expected cooling, prior to the rain appearance sequential
loop brightenings are detected in gradually cooler lines from corona to chromospheric temperatures. Despite the large rain showers,
most cannot be detected in AIA 171 in quadrature, indicating that line-of-sight effects play a major role in coronal rain visibility. Still,
AIA 304 and SPICE observations reveal that only a small fraction of the rain can be captured by HRIEUV.
Conclusions. Coronal rain generates EUV structure and variability over a wide range of scales, from coronal loop to the smallest
resolvable scales. This establishes the major role that TNE-TI plays in the observed EUV morphology and variability of the corona.
Similar to Properties of rubble-pile asteroid (101955) Bennu from OSIRIS-REx imaging and thermal analysis (20)
Compositions of iron-meteorite parent bodies constrainthe structure of the pr...Sérgio Sacani
Magmatic iron-meteorite parent bodies are the earliest planetesimals in the Solar System,and they preserve information about conditions and planet-forming processes in thesolar nebula. In this study, we include comprehensive elemental compositions andfractional-crystallization modeling for iron meteorites from the cores of five differenti-ated asteroids from the inner Solar System. Together with previous results of metalliccores from the outer Solar System, we conclude that asteroidal cores from the outerSolar System have smaller sizes, elevated siderophile-element abundances, and simplercrystallization processes than those from the inner Solar System. These differences arerelated to the formation locations of the parent asteroids because the solar protoplane-tary disk varied in redox conditions, elemental distributions, and dynamics at differentheliocentric distances. Using highly siderophile-element data from iron meteorites, wereconstruct the distribution of calcium-aluminum-rich inclusions (CAIs) across theprotoplanetary disk within the first million years of Solar-System history. CAIs, the firstsolids to condense in the Solar System, formed close to the Sun. They were, however,concentrated within the outer disk and depleted within the inner disk. Future modelsof the structure and evolution of the protoplanetary disk should account for this dis-tribution pattern of CAIs.
Signatures of wave erosion in Titan’s coastsSérgio Sacani
The shorelines of Titan’s hydrocarbon seas trace flooded erosional landforms such as river valleys; however, it isunclear whether coastal erosion has subsequently altered these shorelines. Spacecraft observations and theo-retical models suggest that wind may cause waves to form on Titan’s seas, potentially driving coastal erosion,but the observational evidence of waves is indirect, and the processes affecting shoreline evolution on Titanremain unknown. No widely accepted framework exists for using shoreline morphology to quantitatively dis-cern coastal erosion mechanisms, even on Earth, where the dominant mechanisms are known. We combinelandscape evolution models with measurements of shoreline shape on Earth to characterize how differentcoastal erosion mechanisms affect shoreline morphology. Applying this framework to Titan, we find that theshorelines of Titan’s seas are most consistent with flooded landscapes that subsequently have been eroded bywaves, rather than a uniform erosional process or no coastal erosion, particularly if wave growth saturates atfetch lengths of tens of kilometers.
SDSS1335+0728: The awakening of a ∼ 106M⊙ black hole⋆Sérgio Sacani
Context. The early-type galaxy SDSS J133519.91+072807.4 (hereafter SDSS1335+0728), which had exhibited no prior optical variations during the preceding two decades, began showing significant nuclear variability in the Zwicky Transient Facility (ZTF) alert stream from December 2019 (as ZTF19acnskyy). This variability behaviour, coupled with the host-galaxy properties, suggests that SDSS1335+0728 hosts a ∼ 106M⊙ black hole (BH) that is currently in the process of ‘turning on’. Aims. We present a multi-wavelength photometric analysis and spectroscopic follow-up performed with the aim of better understanding the origin of the nuclear variations detected in SDSS1335+0728. Methods. We used archival photometry (from WISE, 2MASS, SDSS, GALEX, eROSITA) and spectroscopic data (from SDSS and LAMOST) to study the state of SDSS1335+0728 prior to December 2019, and new observations from Swift, SOAR/Goodman, VLT/X-shooter, and Keck/LRIS taken after its turn-on to characterise its current state. We analysed the variability of SDSS1335+0728 in the X-ray/UV/optical/mid-infrared range, modelled its spectral energy distribution prior to and after December 2019, and studied the evolution of its UV/optical spectra. Results. From our multi-wavelength photometric analysis, we find that: (a) since 2021, the UV flux (from Swift/UVOT observations) is four times brighter than the flux reported by GALEX in 2004; (b) since June 2022, the mid-infrared flux has risen more than two times, and the W1−W2 WISE colour has become redder; and (c) since February 2024, the source has begun showing X-ray emission. From our spectroscopic follow-up, we see that (i) the narrow emission line ratios are now consistent with a more energetic ionising continuum; (ii) broad emission lines are not detected; and (iii) the [OIII] line increased its flux ∼ 3.6 years after the first ZTF alert, which implies a relatively compact narrow-line-emitting region. Conclusions. We conclude that the variations observed in SDSS1335+0728 could be either explained by a ∼ 106M⊙ AGN that is just turning on or by an exotic tidal disruption event (TDE). If the former is true, SDSS1335+0728 is one of the strongest cases of an AGNobserved in the process of activating. If the latter were found to be the case, it would correspond to the longest and faintest TDE ever observed (or another class of still unknown nuclear transient). Future observations of SDSS1335+0728 are crucial to further understand its behaviour. Key words. galaxies: active– accretion, accretion discs– galaxies: individual: SDSS J133519.91+072807.4
Discovery of An Apparent Red, High-Velocity Type Ia Supernova at 𝐳 = 2.9 wi...Sérgio Sacani
We present the JWST discovery of SN 2023adsy, a transient object located in a host galaxy JADES-GS
+
53.13485
−
27.82088
with a host spectroscopic redshift of
2.903
±
0.007
. The transient was identified in deep James Webb Space Telescope (JWST)/NIRCam imaging from the JWST Advanced Deep Extragalactic Survey (JADES) program. Photometric and spectroscopic followup with NIRCam and NIRSpec, respectively, confirm the redshift and yield UV-NIR light-curve, NIR color, and spectroscopic information all consistent with a Type Ia classification. Despite its classification as a likely SN Ia, SN 2023adsy is both fairly red (
�
(
�
−
�
)
∼
0.9
) despite a host galaxy with low-extinction and has a high Ca II velocity (
19
,
000
±
2
,
000
km/s) compared to the general population of SNe Ia. While these characteristics are consistent with some Ca-rich SNe Ia, particularly SN 2016hnk, SN 2023adsy is intrinsically brighter than the low-
�
Ca-rich population. Although such an object is too red for any low-
�
cosmological sample, we apply a fiducial standardization approach to SN 2023adsy and find that the SN 2023adsy luminosity distance measurement is in excellent agreement (
≲
1
�
) with
Λ
CDM. Therefore unlike low-
�
Ca-rich SNe Ia, SN 2023adsy is standardizable and gives no indication that SN Ia standardized luminosities change significantly with redshift. A larger sample of distant SNe Ia is required to determine if SN Ia population characteristics at high-
�
truly diverge from their low-
�
counterparts, and to confirm that standardized luminosities nevertheless remain constant with redshift.
Evidence of Jet Activity from the Secondary Black Hole in the OJ 287 Binary S...Sérgio Sacani
Wereport the study of a huge optical intraday flare on 2021 November 12 at 2 a.m. UT in the blazar OJ287. In the binary black hole model, it is associated with an impact of the secondary black hole on the accretion disk of the primary. Our multifrequency observing campaign was set up to search for such a signature of the impact based on a prediction made 8 yr earlier. The first I-band results of the flare have already been reported by Kishore et al. (2024). Here we combine these data with our monitoring in the R-band. There is a big change in the R–I spectral index by 1.0 ±0.1 between the normal background and the flare, suggesting a new component of radiation. The polarization variation during the rise of the flare suggests the same. The limits on the source size place it most reasonably in the jet of the secondary BH. We then ask why we have not seen this phenomenon before. We show that OJ287 was never before observed with sufficient sensitivity on the night when the flare should have happened according to the binary model. We also study the probability that this flare is just an oversized example of intraday variability using the Krakow data set of intense monitoring between 2015 and 2023. We find that the occurrence of a flare of this size and rapidity is unlikely. In machine-readable Tables 1 and 2, we give the full orbit-linked historical light curve of OJ287 as well as the dense monitoring sample of Krakow.
Candidate young stellar objects in the S-cluster: Kinematic analysis of a sub...Sérgio Sacani
Context. The observation of several L-band emission sources in the S cluster has led to a rich discussion of their nature. However, a definitive answer to the classification of the dusty objects requires an explanation for the detection of compact Doppler-shifted Brγ emission. The ionized hydrogen in combination with the observation of mid-infrared L-band continuum emission suggests that most of these sources are embedded in a dusty envelope. These embedded sources are part of the S-cluster, and their relationship to the S-stars is still under debate. To date, the question of the origin of these two populations has been vague, although all explanations favor migration processes for the individual cluster members. Aims. This work revisits the S-cluster and its dusty members orbiting the supermassive black hole SgrA* on bound Keplerian orbits from a kinematic perspective. The aim is to explore the Keplerian parameters for patterns that might imply a nonrandom distribution of the sample. Additionally, various analytical aspects are considered to address the nature of the dusty sources. Methods. Based on the photometric analysis, we estimated the individual H−K and K−L colors for the source sample and compared the results to known cluster members. The classification revealed a noticeable contrast between the S-stars and the dusty sources. To fit the flux-density distribution, we utilized the radiative transfer code HYPERION and implemented a young stellar object Class I model. We obtained the position angle from the Keplerian fit results; additionally, we analyzed the distribution of the inclinations and the longitudes of the ascending node. Results. The colors of the dusty sources suggest a stellar nature consistent with the spectral energy distribution in the near and midinfrared domains. Furthermore, the evaporation timescales of dusty and gaseous clumps in the vicinity of SgrA* are much shorter ( 2yr) than the epochs covered by the observations (≈15yr). In addition to the strong evidence for the stellar classification of the D-sources, we also find a clear disk-like pattern following the arrangements of S-stars proposed in the literature. Furthermore, we find a global intrinsic inclination for all dusty sources of 60 ± 20◦, implying a common formation process. Conclusions. The pattern of the dusty sources manifested in the distribution of the position angles, inclinations, and longitudes of the ascending node strongly suggests two different scenarios: the main-sequence stars and the dusty stellar S-cluster sources share a common formation history or migrated with a similar formation channel in the vicinity of SgrA*. Alternatively, the gravitational influence of SgrA* in combination with a massive perturber, such as a putative intermediate mass black hole in the IRS 13 cluster, forces the dusty objects and S-stars to follow a particular orbital arrangement. Key words. stars: black holes– stars: formation– Galaxy: center– galaxies: star formation
JAMES WEBB STUDY THE MASSIVE BLACK HOLE SEEDSSérgio Sacani
The pathway(s) to seeding the massive black holes (MBHs) that exist at the heart of galaxies in the present and distant Universe remains an unsolved problem. Here we categorise, describe and quantitatively discuss the formation pathways of both light and heavy seeds. We emphasise that the most recent computational models suggest that rather than a bimodal-like mass spectrum between light and heavy seeds with light at one end and heavy at the other that instead a continuum exists. Light seeds being more ubiquitous and the heavier seeds becoming less and less abundant due the rarer environmental conditions required for their formation. We therefore examine the different mechanisms that give rise to different seed mass spectrums. We show how and why the mechanisms that produce the heaviest seeds are also among the rarest events in the Universe and are hence extremely unlikely to be the seeds for the vast majority of the MBH population. We quantify, within the limits of the current large uncertainties in the seeding processes, the expected number densities of the seed mass spectrum. We argue that light seeds must be at least 103 to 105 times more numerous than heavy seeds to explain the MBH population as a whole. Based on our current understanding of the seed population this makes heavy seeds (Mseed > 103 M⊙) a significantly more likely pathway given that heavy seeds have an abundance pattern than is close to and likely in excess of 10−4 compared to light seeds. Finally, we examine the current state-of-the-art in numerical calculations and recent observations and plot a path forward for near-future advances in both domains.
Anti-Universe And Emergent Gravity and the Dark UniverseSérgio Sacani
Recent theoretical progress indicates that spacetime and gravity emerge together from the entanglement structure of an underlying microscopic theory. These ideas are best understood in Anti-de Sitter space, where they rely on the area law for entanglement entropy. The extension to de Sitter space requires taking into account the entropy and temperature associated with the cosmological horizon. Using insights from string theory, black hole physics and quantum information theory we argue that the positive dark energy leads to a thermal volume law contribution to the entropy that overtakes the area law precisely at the cosmological horizon. Due to the competition between area and volume law entanglement the microscopic de Sitter states do not thermalise at sub-Hubble scales: they exhibit memory effects in the form of an entropy displacement caused by matter. The emergent laws of gravity contain an additional ‘dark’ gravitational force describing the ‘elastic’ response due to the entropy displacement. We derive an estimate of the strength of this extra force in terms of the baryonic mass, Newton’s constant and the Hubble acceleration scale a0 = cH0, and provide evidence for the fact that this additional ‘dark gravity force’ explains the observed phenomena in galaxies and clusters currently attributed to dark matter.
The binding of cosmological structures by massless topological defectsSérgio Sacani
Assuming spherical symmetry and weak field, it is shown that if one solves the Poisson equation or the Einstein field
equations sourced by a topological defect, i.e. a singularity of a very specific form, the result is a localized gravitational
field capable of driving flat rotation (i.e. Keplerian circular orbits at a constant speed for all radii) of test masses on a thin
spherical shell without any underlying mass. Moreover, a large-scale structure which exploits this solution by assembling
concentrically a number of such topological defects can establish a flat stellar or galactic rotation curve, and can also deflect
light in the same manner as an equipotential (isothermal) sphere. Thus, the need for dark matter or modified gravity theory is
mitigated, at least in part.
EWOCS-I: The catalog of X-ray sources in Westerlund 1 from the Extended Weste...Sérgio Sacani
Context. With a mass exceeding several 104 M⊙ and a rich and dense population of massive stars, supermassive young star clusters
represent the most massive star-forming environment that is dominated by the feedback from massive stars and gravitational interactions
among stars.
Aims. In this paper we present the Extended Westerlund 1 and 2 Open Clusters Survey (EWOCS) project, which aims to investigate
the influence of the starburst environment on the formation of stars and planets, and on the evolution of both low and high mass stars.
The primary targets of this project are Westerlund 1 and 2, the closest supermassive star clusters to the Sun.
Methods. The project is based primarily on recent observations conducted with the Chandra and JWST observatories. Specifically,
the Chandra survey of Westerlund 1 consists of 36 new ACIS-I observations, nearly co-pointed, for a total exposure time of 1 Msec.
Additionally, we included 8 archival Chandra/ACIS-S observations. This paper presents the resulting catalog of X-ray sources within
and around Westerlund 1. Sources were detected by combining various existing methods, and photon extraction and source validation
were carried out using the ACIS-Extract software.
Results. The EWOCS X-ray catalog comprises 5963 validated sources out of the 9420 initially provided to ACIS-Extract, reaching a
photon flux threshold of approximately 2 × 10−8 photons cm−2
s
−1
. The X-ray sources exhibit a highly concentrated spatial distribution,
with 1075 sources located within the central 1 arcmin. We have successfully detected X-ray emissions from 126 out of the 166 known
massive stars of the cluster, and we have collected over 71 000 photons from the magnetar CXO J164710.20-455217.
The debris of the ‘last major merger’ is dynamically youngSérgio Sacani
The Milky Way’s (MW) inner stellar halo contains an [Fe/H]-rich component with highly eccentric orbits, often referred to as the
‘last major merger.’ Hypotheses for the origin of this component include Gaia-Sausage/Enceladus (GSE), where the progenitor
collided with the MW proto-disc 8–11 Gyr ago, and the Virgo Radial Merger (VRM), where the progenitor collided with the
MW disc within the last 3 Gyr. These two scenarios make different predictions about observable structure in local phase space,
because the morphology of debris depends on how long it has had to phase mix. The recently identified phase-space folds in Gaia
DR3 have positive caustic velocities, making them fundamentally different than the phase-mixed chevrons found in simulations
at late times. Roughly 20 per cent of the stars in the prograde local stellar halo are associated with the observed caustics. Based
on a simple phase-mixing model, the observed number of caustics are consistent with a merger that occurred 1–2 Gyr ago.
We also compare the observed phase-space distribution to FIRE-2 Latte simulations of GSE-like mergers, using a quantitative
measurement of phase mixing (2D causticality). The observed local phase-space distribution best matches the simulated data
1–2 Gyr after collision, and certainly not later than 3 Gyr. This is further evidence that the progenitor of the ‘last major merger’
did not collide with the MW proto-disc at early times, as is thought for the GSE, but instead collided with the MW disc within
the last few Gyr, consistent with the body of work surrounding the VRM.
Observation of Io’s Resurfacing via Plume Deposition Using Ground-based Adapt...Sérgio Sacani
Since volcanic activity was first discovered on Io from Voyager images in 1979, changes
on Io’s surface have been monitored from both spacecraft and ground-based telescopes.
Here, we present the highest spatial resolution images of Io ever obtained from a groundbased telescope. These images, acquired by the SHARK-VIS instrument on the Large
Binocular Telescope, show evidence of a major resurfacing event on Io’s trailing hemisphere. When compared to the most recent spacecraft images, the SHARK-VIS images
show that a plume deposit from a powerful eruption at Pillan Patera has covered part
of the long-lived Pele plume deposit. Although this type of resurfacing event may be common on Io, few have been detected due to the rarity of spacecraft visits and the previously low spatial resolution available from Earth-based telescopes. The SHARK-VIS instrument ushers in a new era of high resolution imaging of Io’s surface using adaptive
optics at visible wavelengths.
Earliest Galaxies in the JADES Origins Field: Luminosity Function and Cosmic ...Sérgio Sacani
We characterize the earliest galaxy population in the JADES Origins Field (JOF), the deepest
imaging field observed with JWST. We make use of the ancillary Hubble optical images (5 filters
spanning 0.4−0.9µm) and novel JWST images with 14 filters spanning 0.8−5µm, including 7 mediumband filters, and reaching total exposure times of up to 46 hours per filter. We combine all our data
at > 2.3µm to construct an ultradeep image, reaching as deep as ≈ 31.4 AB mag in the stack and
30.3-31.0 AB mag (5σ, r = 0.1” circular aperture) in individual filters. We measure photometric
redshifts and use robust selection criteria to identify a sample of eight galaxy candidates at redshifts
z = 11.5 − 15. These objects show compact half-light radii of R1/2 ∼ 50 − 200pc, stellar masses of
M⋆ ∼ 107−108M⊙, and star-formation rates of SFR ∼ 0.1−1 M⊙ yr−1
. Our search finds no candidates
at 15 < z < 20, placing upper limits at these redshifts. We develop a forward modeling approach to
infer the properties of the evolving luminosity function without binning in redshift or luminosity that
marginalizes over the photometric redshift uncertainty of our candidate galaxies and incorporates the
impact of non-detections. We find a z = 12 luminosity function in good agreement with prior results,
and that the luminosity function normalization and UV luminosity density decline by a factor of ∼ 2.5
from z = 12 to z = 14. We discuss the possible implications of our results in the context of theoretical
models for evolution of the dark matter halo mass function.
THE IMPORTANCE OF MARTIAN ATMOSPHERE SAMPLE RETURN.Sérgio Sacani
The return of a sample of near-surface atmosphere from Mars would facilitate answers to several first-order science questions surrounding the formation and evolution of the planet. One of the important aspects of terrestrial planet formation in general is the role that primary atmospheres played in influencing the chemistry and structure of the planets and their antecedents. Studies of the martian atmosphere can be used to investigate the role of a primary atmosphere in its history. Atmosphere samples would also inform our understanding of the near-surface chemistry of the planet, and ultimately the prospects for life. High-precision isotopic analyses of constituent gases are needed to address these questions, requiring that the analyses are made on returned samples rather than in situ.
Multi-source connectivity as the driver of solar wind variability in the heli...Sérgio Sacani
The ambient solar wind that flls the heliosphere originates from multiple
sources in the solar corona and is highly structured. It is often described
as high-speed, relatively homogeneous, plasma streams from coronal
holes and slow-speed, highly variable, streams whose source regions are
under debate. A key goal of ESA/NASA’s Solar Orbiter mission is to identify
solar wind sources and understand what drives the complexity seen in the
heliosphere. By combining magnetic feld modelling and spectroscopic
techniques with high-resolution observations and measurements, we show
that the solar wind variability detected in situ by Solar Orbiter in March
2022 is driven by spatio-temporal changes in the magnetic connectivity to
multiple sources in the solar atmosphere. The magnetic feld footpoints
connected to the spacecraft moved from the boundaries of a coronal hole
to one active region (12961) and then across to another region (12957). This
is refected in the in situ measurements, which show the transition from fast
to highly Alfvénic then to slow solar wind that is disrupted by the arrival of
a coronal mass ejection. Our results describe solar wind variability at 0.5 au
but are applicable to near-Earth observatories.
Gliese 12 b: A Temperate Earth-sized Planet at 12 pc Ideal for Atmospheric Tr...Sérgio Sacani
Recent discoveries of Earth-sized planets transiting nearby M dwarfs have made it possible to characterize the
atmospheres of terrestrial planets via follow-up spectroscopic observations. However, the number of such planets
receiving low insolation is still small, limiting our ability to understand the diversity of the atmospheric
composition and climates of temperate terrestrial planets. We report the discovery of an Earth-sized planet
transiting the nearby (12 pc) inactive M3.0 dwarf Gliese 12 (TOI-6251) with an orbital period (Porb) of 12.76 days.
The planet, Gliese 12 b, was initially identified as a candidate with an ambiguous Porb from TESS data. We
confirmed the transit signal and Porb using ground-based photometry with MuSCAT2 and MuSCAT3, and
validated the planetary nature of the signal using high-resolution images from Gemini/NIRI and Keck/NIRC2 as
well as radial velocity (RV) measurements from the InfraRed Doppler instrument on the Subaru 8.2 m telescope
and from CARMENES on the CAHA 3.5 m telescope. X-ray observations with XMM-Newton showed the host
star is inactive, with an X-ray-to-bolometric luminosity ratio of log 5.7 L L X bol » - . Joint analysis of the light
curves and RV measurements revealed that Gliese 12 b has a radius of 0.96 ± 0.05 R⊕,a3σ mass upper limit of
3.9 M⊕, and an equilibrium temperature of 315 ± 6 K assuming zero albedo. The transmission spectroscopy metric
(TSM) value of Gliese 12 b is close to the TSM values of the TRAPPIST-1 planets, adding Gliese 12 b to the small
list of potentially terrestrial, temperate planets amenable to atmospheric characterization with JWST.
The importance of continents, oceans and plate tectonics for the evolution of...Sérgio Sacani
Within the uncertainties of involved astronomical and biological parameters, the Drake Equation
typically predicts that there should be many exoplanets in our galaxy hosting active, communicative
civilizations (ACCs). These optimistic calculations are however not supported by evidence, which is
often referred to as the Fermi Paradox. Here, we elaborate on this long-standing enigma by showing
the importance of planetary tectonic style for biological evolution. We summarize growing evidence
that a prolonged transition from Mesoproterozoic active single lid tectonics (1.6 to 1.0 Ga) to modern
plate tectonics occurred in the Neoproterozoic Era (1.0 to 0.541 Ga), which dramatically accelerated
emergence and evolution of complex species. We further suggest that both continents and oceans
are required for ACCs because early evolution of simple life must happen in water but late evolution
of advanced life capable of creating technology must happen on land. We resolve the Fermi Paradox
(1) by adding two additional terms to the Drake Equation: foc
(the fraction of habitable exoplanets
with significant continents and oceans) and fpt
(the fraction of habitable exoplanets with significant
continents and oceans that have had plate tectonics operating for at least 0.5 Ga); and (2) by
demonstrating that the product of foc
and fpt
is very small (< 0.00003–0.002). We propose that the lack
of evidence for ACCs reflects the scarcity of long-lived plate tectonics and/or continents and oceans on
exoplanets with primitive life.
A Giant Impact Origin for the First Subduction on EarthSérgio Sacani
Hadean zircons provide a potential record of Earth's earliest subduction 4.3 billion years ago. Itremains enigmatic how subduction could be initiated so soon after the presumably Moon‐forming giant impact(MGI). Earlier studies found an increase in Earth's core‐mantle boundary (CMB) temperature due to theaccumulation of the impactor's core, and our recent work shows Earth's lower mantle remains largely solid, withsome of the impactor's mantle potentially surviving as the large low‐shear velocity provinces (LLSVPs). Here,we show that a hot post‐impact CMB drives the initiation of strong mantle plumes that can induce subductioninitiation ∼200 Myr after the MGI. 2D and 3D thermomechanical computations show that a high CMBtemperature is the primary factor triggering early subduction, with enrichment of heat‐producing elements inLLSVPs as another potential factor. The models link the earliest subduction to the MGI with implications forunderstanding the diverse tectonic regimes of rocky planets.
Climate extremes likely to drive land mammal extinction during next supercont...Sérgio Sacani
Mammals have dominated Earth for approximately 55 Myr thanks to their
adaptations and resilience to warming and cooling during the Cenozoic. All
life will eventually perish in a runaway greenhouse once absorbed solar
radiation exceeds the emission of thermal radiation in several billions of
years. However, conditions rendering the Earth naturally inhospitable to
mammals may develop sooner because of long-term processes linked to
plate tectonics (short-term perturbations are not considered here). In
~250 Myr, all continents will converge to form Earth’s next supercontinent,
Pangea Ultima. A natural consequence of the creation and decay of Pangea
Ultima will be extremes in pCO2 due to changes in volcanic rifting and
outgassing. Here we show that increased pCO2, solar energy (F⨀;
approximately +2.5% W m−2 greater than today) and continentality (larger
range in temperatures away from the ocean) lead to increasing warming
hostile to mammalian life. We assess their impact on mammalian
physiological limits (dry bulb, wet bulb and Humidex heat stress indicators)
as well as a planetary habitability index. Given mammals’ continued survival,
predicted background pCO2 levels of 410–816 ppm combined with increased
F⨀ will probably lead to a climate tipping point and their mass extinction.
The results also highlight how global landmass configuration, pCO2 and F⨀
play a critical role in planetary habitability.
Constraints on Neutrino Natal Kicks from Black-Hole Binary VFTS 243Sérgio Sacani
The recently reported observation of VFTS 243 is the first example of a massive black-hole binary
system with negligible binary interaction following black-hole formation. The black-hole mass (≈10M⊙)
and near-circular orbit (e ≈ 0.02) of VFTS 243 suggest that the progenitor star experienced complete
collapse, with energy-momentum being lost predominantly through neutrinos. VFTS 243 enables us to
constrain the natal kick and neutrino-emission asymmetry during black-hole formation. At 68% confidence
level, the natal kick velocity (mass decrement) is ≲10 km=s (≲1.0M⊙), with a full probability distribution
that peaks when ≈0.3M⊙ were ejected, presumably in neutrinos, and the black hole experienced a natal
kick of 4 km=s. The neutrino-emission asymmetry is ≲4%, with best fit values of ∼0–0.2%. Such a small
neutrino natal kick accompanying black-hole formation is in agreement with theoretical predictions.
The cost of acquiring information by natural selectionCarl Bergstrom
This is a short talk that I gave at the Banff International Research Station workshop on Modeling and Theory in Population Biology. The idea is to try to understand how the burden of natural selection relates to the amount of information that selection puts into the genome.
It's based on the first part of this research paper:
The cost of information acquisition by natural selection
Ryan Seamus McGee, Olivia Kosterlitz, Artem Kaznatcheev, Benjamin Kerr, Carl T. Bergstrom
bioRxiv 2022.07.02.498577; doi: https://doi.org/10.1101/2022.07.02.498577
Authoring a personal GPT for your research and practice: How we created the Q...Leonel Morgado
Thematic analysis in qualitative research is a time-consuming and systematic task, typically done using teams. Team members must ground their activities on common understandings of the major concepts underlying the thematic analysis, and define criteria for its development. However, conceptual misunderstandings, equivocations, and lack of adherence to criteria are challenges to the quality and speed of this process. Given the distributed and uncertain nature of this process, we wondered if the tasks in thematic analysis could be supported by readily available artificial intelligence chatbots. Our early efforts point to potential benefits: not just saving time in the coding process but better adherence to criteria and grounding, by increasing triangulation between humans and artificial intelligence. This tutorial will provide a description and demonstration of the process we followed, as two academic researchers, to develop a custom ChatGPT to assist with qualitative coding in the thematic data analysis process of immersive learning accounts in a survey of the academic literature: QUAL-E Immersive Learning Thematic Analysis Helper. In the hands-on time, participants will try out QUAL-E and develop their ideas for their own qualitative coding ChatGPT. Participants that have the paid ChatGPT Plus subscription can create a draft of their assistants. The organizers will provide course materials and slide deck that participants will be able to utilize to continue development of their custom GPT. The paid subscription to ChatGPT Plus is not required to participate in this workshop, just for trying out personal GPTs during it.
BIRDS DIVERSITY OF SOOTEA BISWANATH ASSAM.ppt.pptxgoluk9330
Ahota Beel, nestled in Sootea Biswanath Assam , is celebrated for its extraordinary diversity of bird species. This wetland sanctuary supports a myriad of avian residents and migrants alike. Visitors can admire the elegant flights of migratory species such as the Northern Pintail and Eurasian Wigeon, alongside resident birds including the Asian Openbill and Pheasant-tailed Jacana. With its tranquil scenery and varied habitats, Ahota Beel offers a perfect haven for birdwatchers to appreciate and study the vibrant birdlife that thrives in this natural refuge.
Immersive Learning That Works: Research Grounding and Paths ForwardLeonel Morgado
We will metaverse into the essence of immersive learning, into its three dimensions and conceptual models. This approach encompasses elements from teaching methodologies to social involvement, through organizational concerns and technologies. Challenging the perception of learning as knowledge transfer, we introduce a 'Uses, Practices & Strategies' model operationalized by the 'Immersive Learning Brain' and ‘Immersion Cube’ frameworks. This approach offers a comprehensive guide through the intricacies of immersive educational experiences and spotlighting research frontiers, along the immersion dimensions of system, narrative, and agency. Our discourse extends to stakeholders beyond the academic sphere, addressing the interests of technologists, instructional designers, and policymakers. We span various contexts, from formal education to organizational transformation to the new horizon of an AI-pervasive society. This keynote aims to unite the iLRN community in a collaborative journey towards a future where immersive learning research and practice coalesce, paving the way for innovative educational research and practice landscapes.
ESA/ACT Science Coffee: Diego Blas - Gravitational wave detection with orbita...Advanced-Concepts-Team
Presentation in the Science Coffee of the Advanced Concepts Team of the European Space Agency on the 07.06.2024.
Speaker: Diego Blas (IFAE/ICREA)
Title: Gravitational wave detection with orbital motion of Moon and artificial
Abstract:
In this talk I will describe some recent ideas to find gravitational waves from supermassive black holes or of primordial origin by studying their secular effect on the orbital motion of the Moon or satellites that are laser ranged.
CLASS 12th CHEMISTRY SOLID STATE ppt (Animated)eitps1506
Description:
Dive into the fascinating realm of solid-state physics with our meticulously crafted online PowerPoint presentation. This immersive educational resource offers a comprehensive exploration of the fundamental concepts, theories, and applications within the realm of solid-state physics.
From crystalline structures to semiconductor devices, this presentation delves into the intricate principles governing the behavior of solids, providing clear explanations and illustrative examples to enhance understanding. Whether you're a student delving into the subject for the first time or a seasoned researcher seeking to deepen your knowledge, our presentation offers valuable insights and in-depth analyses to cater to various levels of expertise.
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TOPIC OF DISCUSSION: CENTRIFUGATION SLIDESHARE.pptxshubhijain836
Centrifugation is a powerful technique used in laboratories to separate components of a heterogeneous mixture based on their density. This process utilizes centrifugal force to rapidly spin samples, causing denser particles to migrate outward more quickly than lighter ones. As a result, distinct layers form within the sample tube, allowing for easy isolation and purification of target substances.
Properties of rubble-pile asteroid (101955) Bennu from OSIRIS-REx imaging and thermal analysis
1. Articles
https://doi.org/10.1038/s41550-019-0731-1
1
Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA. 2
Department of Earth and Planetary Sciences, University of Tennessee, Knoxville,
TN, USA. 3
School of Physical Sciences, The Open University, Milton Keynes, UK. 4
School of Earth and Space Exploration, Arizona State University, Tempe,
AZ, USA. 5
Southwest Research Institute, Boulder, CO, USA. 6
NASA Goddard Space Flight Center, Greenbelt, MD, USA. 7
Space Science Institute, Boulder,
CO, USA. 8
The Johns Hopkins University Applied Physics Laboratory, Laurel, MD, USA. 9
LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne
Université, Univ. Paris Diderot, Sorbonne Paris Cité, Meudon, France. 10
Lockheed Martin Space, Littleton, CO, USA. 11
Department of Earth, Atmospheric,
and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA, USA. 12
Atmospheric, Oceanic and Planetary Physics, University of Oxford,
Oxford, UK. 13
Department of Physics, University of Central Florida, Orlando, FL, USA. 14
Department of Physics and Astronomy, Ithaca College, Ithaca, NY,
USA. 15
Department of Geology, Rowan University, Glassboro, NJ, USA. 16
The Centre for Research in Earth and Space Science, York University, Toronto,
Ontario, Canada. 17
Instituto de Astrofísica de Canarias and Departamento de Astrofísica, Universidad de La Laguna, Tenerife, Spain. 18
Université Côte
d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, Nice, France. 19
Jet Propulsion Laboratory, California Institute of Technology, Pasadena,
CA, USA. 20
Smithsonian Institution National Museum of Natural History, Washington, DC, USA. 21
Planetary Science Institute, Tucson, AZ, USA. 22
Istituto
Nazionale di Astrofisica, Astronomical Observatory of Padova, Padova, Italy. 23
Department of Earth and Planetary Science, The University of Tokyo, Tokyo,
Japan. 24
Department of Physics and Astronomy, Northern Arizona University, Flagstaff, AZ, USA. 25
A full list of authors and their affiliations appears at the
end of the paper. 26
These authors contributed equally: D. N. DellaGiustina, J. P. Emery. *e-mail: danidg@lpl.arizona.edu; jemery2@utk.edu
B
efore the OSIRIS-REx mission, expectations for the distribution
of regolith on small near-Earth asteroids (NEAs) came from
(25143) Itokawa and (162173) Ryugu. The surfaces of both of
these NEAs are dominated by boulders, but smooth terrains are evi-
dent at global scales. Prior to resolving its surface, our understanding
of Bennu’s global properties was inferred from telescopic observa-
tions of the asteroid as a point source1
. In late 2018, the OSIRIS-
REx spacecraft rendezvoused with asteroid (101955) Bennu and
acquired remotely sensed image and spectral data. The OSIRIS-REx
Camera Suite (OCAMS2
) PolyCam panchromatic camera confirmed
the top-like shape of the asteroid3
and imaged the surface at scales
down to 0.33 m pixel–1
, while the MapCam instrument imaged at
scales down to 1.1 m pixel–1
in four colours and a panchromatic fil-
ter. The OSIRIS-REx Visible and InfraRed Spectrometer (OVIRS4
)
and the OSIRIS-REx Thermal Emission Spectrometer (OTES5
) mea-
sured disk-integrated spectra covering a full asteroid rotation before
Bennu filled their respective fields of view.
Global average properties
During the Approach and Preliminary Survey phases of the mission
(August to December 2018), we measured Bennu’s resolved reflec-
tance (radiance factor, often referred to as I/F) in MapCam’s five
filters across a wide range of phase angles (0.7° to 90°). Fitting these
data to an exponential phase function6
yields a low global average
geometric albedo of 4.4 ± 0.2% at 550 nm (Fig. 1a). This albedo is
consistent with ground-based astronomical data7
, B-type asteroid
taxonomy8
, and results from OSIRIS-REx disk-integrated photom-
etry9
. The global albedo is also compatible with the reflectance of
CM chondrite meteorites10
, which are spectroscopically similar to
Bennu11
. Bennu does not exhibit a significant opposition surge at
Properties of rubble-pile asteroid (101955) Bennu
from OSIRIS-REx imaging and thermal analysis
D. N. DellaGiustina 1,26
*, J. P. Emery 2,26
*, D. R. Golish1
, B. Rozitis3
, C. A. Bennett1
, K. N. Burke 1
,
R.-L. Ballouz 1
, K. J. Becker 1
, P. R. Christensen4
, C. Y. Drouet d’Aubigny1
, V. E. Hamilton 5
,
D. C. Reuter6
, B. Rizk 1
, A. A. Simon6
, E. Asphaug1
, J. L. Bandfield 7
, O. S. Barnouin 8
, M. A. Barucci 9
,
E. B. Bierhaus10
, R. P. Binzel11
, W. F. Bottke5
, N. E. Bowles12
, H. Campins13
, B. C. Clark7
, B. E. Clark14
,
H. C. Connolly Jr. 15
, M. G. Daly 16
, J. de Leon 17
, M. Delbo’18
, J. D. P. Deshapriya9
, C. M. Elder19
,
S. Fornasier9
, C. W. Hergenrother1
, E. S. Howell1
, E. R. Jawin20
, H. H. Kaplan5
, T. R. Kareta 1
, L. Le Corre 21
,
J.-Y. Li21
, J. Licandro17
, L. F. Lim6
, P. Michel 18
, J. Molaro21
, M. C. Nolan 1
, M. Pajola 22
, M. Popescu 17
,
J. L. Rizos Garcia 17
, A. Ryan18
, S. R. Schwartz 1
, N. Shultz1
, M. A. Siegler21
, P. H. Smith1
, E. Tatsumi23
,
C. A. Thomas24
, K. J. Walsh 5
, C. W. V. Wolner1
, X.-D. Zou21
, D. S. Lauretta 1
and The OSIRIS-REx Team25
Establishing the abundance and physical properties of regolith and boulders on asteroids is crucial for understanding the for-
mation and degradation mechanisms at work on their surfaces. Using images and thermal data from NASA’s Origins, Spectral
Interpretation, Resource Identification, and Security-Regolith Explorer (OSIRIS-REx) spacecraft, we show that asteroid
(101955) Bennu’s surface is globally rough, dense with boulders, and low in albedo. The number of boulders is surprising given
Bennu’s moderate thermal inertia, suggesting that simple models linking thermal inertia to particle size do not adequately cap-
ture the complexity relating these properties. At the same time, we find evidence for a wide range of particle sizes with distinct
albedo characteristics. Our findings imply that ages of Bennu’s surface particles span from the disruption of the asteroid’s par-
ent body (boulders) to recent in situ production (micrometre-scale particles).
Nature Astronomy | www.nature.com/natureastronomy
2. Articles NATURE ASTROnOmy
low phase angles. The absence of a strong opposition effect is not
surprising given the low albedo and thus single-scattering nature
of the surface6
.
During Approach, we also acquired disk-integrated and rota-
tionally resolved measurements of Bennu’s thermal radiance from
OVIRS and OTES. From these data, we determine a global average
thermalinertiaof350 ± 20 J m–2
K–1
s–1/2
(SupplementaryFigs.1and2,
Methods, and Supplementary Information). The OSIRIS-REx ther-
mal data constrain thermal inertia variations to <10 J m–2
K–1
s–1/2
over a full rotation. The low to moderate thermal inertia and small
variability with rotation are within the uncertainties of previous
results based on observations with the Spitzer Space Telescope12
.
The thermal inertia of asteroid surfaces is often translated into
a characteristic particle size using simplified models that assume
a uniform particulate regolith12–14
. The basis for these models is
that particles smaller than the diurnal thermal skin depth will pro-
duce a thermal inertia smaller than the value for bedrock (1,500
to 2,500 J m–2
K–1
s–1/2
for typical planetary materials15,16
). For the
moderate thermal inertia measured for Bennu, these models pre-
dict a surface dominated by 0.5- to 5-cm-diameter particles (see
Methods and Supplementary Information). However, resolved
images of Bennu’s surface show that it is in fact dominated by
>1-m boulders (Fig. 2).
These simplistic regolith models clearly do not accurately
describe Bennu’s surface. Below, we discuss other possible interpre-
tations of Bennu’s thermal inertia, including low thermal inertia of
boulders, dust cover on boulders, a mixture of particulate regolith
and boulders, or a combination of these effects.
Spatially resolved surface morphology
Bennu is geomorphologically diverse (Fig. 2), cratered, and covered
by rocks with a wide range of sizes, consistent with its characteriza-
tion as a rubble-pile asteroid17
. Impact craters range in size from 10
to over 150 m (ref. 18
), and the surface is populated by more than
200 boulders >10 m in diameter. The largest boulders exceed 30 m
and appear predominantly at high latitudes. Smaller metre-scale
boulders are evenly distributed across the asteroid, consistent with
the uniform thermal inertia with rotation. Boulders display a wide
range of morphology, sizes, and albedo. One of the darkest objects
is the partially exposed outcrop of a boulder in the southern (–Z)
hemisphere (–20° latitude, 30° longitude), perhaps a constituent
component of the asteroid. It measures nearly 100 m in observ-
able longest dimension, but its full extent is unclear. Bennu exhibits
only small areas (<20 m) of boulder-free regolith19
, contrary to pre-
encounter expectations1,12,20
.
We have completed boulder counts and size measurements over
>80% of the asteroid’s surface (Supplementary Fig. 3). The mea-
sured sizes of the boulders range from 1 to 58 m (longest dimension).
Figure 3 depicts the global cumulative size-frequency distribution
(CSFD) of Bennu. We find a power-law index of –2.9 ± 0.3 for boul-
ders 8 m and larger (see Methods for a discussion of the statistical
completeness limit). This power-law index is within the range of
other small Solar System bodies (Supplementary Fig. 4).
By comparison, asteroid (25143) Itokawa has a global power-law
index of –3.5 ± 0.121
for boulders ≥10 m, which implies that more
of its surface mass is contained in small particles than is the case
for Bennu. This is consistent with the distinct appearance of these
two asteroids—Bennu lacks Itokawa’s smooth regions such as the
Muses Sea22
. However, the absolute number density of large boul-
ders (≥20 m) on Bennu and Itokawa is comparable (28.2 km–2
versus
~25 km–2
)21,22
. Conversely, the number density of boulders ≥20 m on
(162173) Ryugu (~50 km–2
), the slightly larger top-shaped target of
the Hayabusa2 mission, is twice that of Bennu and Itokawa. Like
Bennu, Ryugu has a power-law index of –2.5 to –3.0. The num-
ber densities of large boulders suggest that boulder abundance on
rubble-pile NEAs scales with asteroid size, whereas the steeper
power-law index on bi-lobed Itokawa suggests that surface particle
distributions may be influenced by asteroid shape. Notably, the dis-
tribution of the large boulders (≥20 m) at high latitudes on Bennu
corresponds with a steepening in the dynamic surface slope outside
the equatorial latitudes23
. Accordingly, material from mid-latitude
to polar regions is less energetically coupled to the surface of the
0 10 20 30 40 50 60 70 80 90
Phase angle (°)
0
0.005
0.010
0.015
0.020
0.025
0.030
0.035
0.040
0.045
0.050
ReflectanceI/F
MapCam, pan
MapCam, b' band
MapCam, v band
MapCam, w band
MapCam, x band
Average phase curve
0 10 20 30 40 50 60 70 80 90
Phase angle (°)
0.97
0.98
0.99
1.00
1.01
1.02
1.03
1.04
1.05
Relativereflectance
b'/v band ratio
w/v band ratio
x/v band ratio
a b
Fig. 1 | Resolved phase curves of Bennu. a, Global reflectance values of Bennu’s surface as a function of phase angle, which convey Bennu’s photometric
behaviour. We fit these data to an exponential phase function for each MapCam band. For clarity, the phase function of the spectral average is shown as
a dashed line. b, Spectral dependence is observed when reflectance for the b′ (473 nm), w (698 nm) and x (847 nm) bands are plotted relative to the v
band (550 nm) at 0° phase angle. The positive slope in the w and x data, and negative slope in the b′ data, demonstrate phase reddening. The error bars
represent 1σ uncertainties.
Nature Astronomy | www.nature.com/natureastronomy
3. ArticlesNATURE ASTROnOmy
asteroid23
. As a result, smaller particles may preferentially migrate
away from these areas, resulting in the exhumation and retention of
larger boulders at higher latitudes.
A shallow power-law index suggests boulder production domi-
nated by impact processes24
. While multiple candidate impact cra-
ters18
are visible across the surface (Fig. 2), the events that formed
them could not produce the large observed boulder population
(Supplementary Fig. 5). The presence of intact blocks about 1/10th
of the diameter of Bennu suggests that the largest boulders are frag-
ments from the catastrophic disruption of its parent body and the
subsequent rubble-pile reaccumulation18,25
. Thus, the large (≥20 m)
boulders evident in Bennu’s relatively shallow CSFD represent some
of the oldest intact material on the surface. Although boulders
<20 m may have been inherited by the catastrophic disruption of
Bennu’s parent body, it is likely that some were formed by impacts
on Bennu’s own surface, and may have experienced further in situ
breakdown and disaggregation by thermal fatigue26
.
Physical properties of boulders
Bennu’s thermal inertia may be conveying information about the
physical properties of its large surface boulders. One interpretation
of the moderate thermal inertia is that the large boulders could
have a lower thermal inertia than typical planetary materials. Any
property that impedes the thermal wave in the material could lower
the thermal inertia (for example, porosity, cement between clasts
of a breccia, amorphous material). For example, the CM chondrite
Cold Bokkeveld has a low thermal conductivity and correspond-
ingly low thermal inertia (~770 J m–2
K–1
s–1/2
)16
due its porosity
(~15%)27
. The hypothesis that Bennu’s boulders themselves have
a relatively low thermal inertia is supported by the close spectral
match of Bennu’s surface to CM chondrites11
. However, the ther-
mal inertia of Cold Bokkeveld (the lowest among measured mete-
orites27
) is still considerably larger than Bennu’s global value. We
investigated the thermal inertia of the boulders on Bennu by run-
ning a two-component thermal model constrained by the spatial
density of boulders18
. We find that the upper limit on the average
boulder thermal inertia on Bennu is 1,400 J m–2
K–1
s–1/2
. We will
measure thermal inertia of individual boulders from upcoming
spatially resolved thermal observations.
The global thermal inertia of Itokawa (750 J m–2
K–1
s–1/2
)28
is more
than twice Bennu’s, even though the number density of large boul-
ders is comparable. The shallower CSFD power-law index on Bennu
suggests that it may have fewer centimetre-scale particles than
Itokawa. Although it is not yet known whether Bennu’s CSFD main-
tains a constant power-law index from 8 m to 2 cm, analyses of rego-
lith on other asteroids suggest constant power laws across similar
scales29
. The lower thermal inertia and relative deficit of small par-
ticles on Bennu, in turn, suggest that the boulders may have a lower
70
60
50
40
30
20
10
0°
–10
–20
–30
–40
–50
–60
–70
0° 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 210 220 230 240 250 260 270 280 290 300 310 320 330 340 350 360
a
Longitude
Latitude
b
Fig. 2 | Asteroid Bennu imaged by the OSIRIS-REx Camera Suite. a, Whole-disk mosaics of Bennu. PolyCam images from 2 December 2018 are
combined to show four sides of Bennu. When viewed from left to right these data illustrate one rotation of the asteroid. Phase angles of the images are
between 47.72° and 51.91°, and pixel scales are between 0.509 and 2.926 m pixel–1
. b, Global equirectangular map of Bennu. PolyCam images acquired on
1 December 2018 (phase angle range of 33.22° and 35.76° and pixel scales between 0.743 and 3.866 m pixel–1
) are combined with MapCam images from
13 December 2018, (phase angle range of 38.15° to 52.01° and pixel scales between 1.331 to 1.885 m pixel–1
) and mosaicked into this equirectangular map of
Bennu. North is defined as the +Z pole and points to the top of the image.
Nature Astronomy | www.nature.com/natureastronomy
4. Articles NATURE ASTROnOmy
thermal inertia than those on Itokawa. Different thermal inertias
of boulders on S-type versus B-type asteroids are consistent with
differences in the thermal conductivity of their respective analogue
meteorites27
. Density and heat capacity also influence thermal iner-
tia, but their variation among meteorite analogues is much smaller
than that of thermal conductivity. Although the boulder abundance
on Ryugu is about twice that on Bennu and the CSFD indices are
similar, Ryugu’s thermal inertia is 200 to 500 J m–2
K–1
s–1/2
(refs. 30,31
),
suggesting that its boulders may have similar thermal inertia to
Bennu’s. Porosity tends to have a stronger control on thermal iner-
tia than composition27
, so the difference in Itokawa’s global thermal
inertia compared with Bennu’s and Ryugu’s could result from dis-
tinct porosities of their boulders.
Boulders are a major source of albedo heterogeneity on Bennu.
The full range of normal albedo variation is more than a factor of
4 (from 3.3% to 15%), though 95% of the range is between 3.6%
to 4.8% (a factor of 1.5)19
. This diversity is greater than on Ryugu,
which has a similar global geometric albedo to Bennu31
. The total
range also exceeds that observed on Itokawa (factor of 1.3)32
and
Eros (factor of 3.5)33
. Because much of Bennu’s albedo variation
appears linked to boulder size, trends in albedo may help us assess
the properties of these boulders. Figure 4a shows the normal albedo
distribution of boulders identified to date. The largest boulders have
albedos near the global average, whereas the brightest boulders
(>1σ from the mean boulder albedo, or >6.8%) are all smaller than
~10 m. Although we are only sampling a small number of bright
boulders (~370), our data show a clear difference in the size distri-
butions of bright versus average-to-dark boulders (Fig. 4b).
This distinct size distribution has several potential origins. Much
of the spectrophotometric variation observed on airless bodies has
been attributed to radiation and bombardment processes collec-
tively referred to as ‘space weathering’. For example, on asteroid
(433) Eros, colour and reflectance differences are not explained
by distinct rock types, but rather by complex regolith sorting and
space weathering processes34
. One study35
that investigated solar-
wind-induced space weathering outcomes for CI/CM chondrites
predicted that bluer and brighter regions on Bennu could represent
more weathered material, although results from laser irradiation
experiments show the opposite36
. Given that the large (>30 m) boul-
ders represent intact material from Bennu’s parent body, their aver-
age albedo may signify older surfaces that have been more optically
modified. Smaller and brighter boulders may represent younger,
more recently fragmented material.
Another possibility is that bright material represents remnants of
Bennu’s parent body or the impactor that disrupted it, which reac-
creted into Bennu and other small asteroids. This scenario would
imply that the observed heterogeneity is the result of distinct rock
types, which fragment differently, leading to the observed differ-
ences in size distribution. Some clues are provided from evidence of
bright clasts bound in a matrix19
and in situ boulder disaggregation
into resistant constituent clasts (Fig. 5). Some clasts have a range
of albedos that differ from the surrounding terrain, implying that
some of the albedo diversity on Bennu is inherited19
.
Evidence of particulate regolith
We observe diffuse units of dark material that we interpret as low-
albedo dust blanketing the surface (Fig. 6 and Supplementary Fig. 6).
The dark diffuse unit shown in Fig. 6 is proximal to the partially
exposed boulder outcrop (discussed above), which is one of the
darkest objects on the asteroid and shows a spectral feature at
550 nm19
. This spectral feature may be due to enhanced magnetite
concentrations generated as a byproduct of space weathering19
. Our
observation of dark dust cover strengthens this finding by supply-
ing evidence that it is compositionally distinct. Laboratory studies
show that the reflectance of CM chondrite powders increases with
decreasing particle size37
. Thus, dust generated from mechanical
breakdown on Bennu should be brighter, and for dust to be darker
than the surroundings it likely has a different composition. However,
the mechanism for transporting fine material from a composition-
ally distinct reservoir to nearby terrains remains unclear.
Furthermore, the presence of particulate regolith mixed with the
observed boulders could explain the moderate thermal inertia. If
such fine particulate material manifested as a dust (particle size less
than a few tens of micrometres) coating on boulders, as we observe,
it would result in a masking of the higher-thermal-inertia signature
expectedfromlargeboulders.Dustcoatingsafewtensto100μmthick
affect thermal signatures (J. Biel et al., manuscript in preparation).
Particulates may also be present as coarser regolith between boul-
ders or as a combination of dust coating and coarser interstitial
regolith. Indeed, images of the surface reveal some areas that appear
smooth at current pixel scales (0.33 m pixel–1
)19
, indicating the pres-
ence of particulate regolith.
The global scattering properties of Bennu obtained from spectro-
photometric modelling reveal additional evidence of small particles.
The spectral dependence of Bennu’s phase curve is nearly flat to within
the radiometric precision of OCAMS (Fig. 1a). In relative compari-
sons between the OCAMS colours, however, Bennu reddens at higher
phase angles (Fig. 1b), as has been observed on several other aster-
oids38,39
. Bennu’s low albedo does not favour multiple scattering, which
has been invoked to explain phase reddening40
. Although single scat-
tering is typically considered to have a weak wavelength dependence,
it has been suggested39
that wavelength-dependent single scattering on
low-albedo surfaces might be due to micrometre-scale particles. This
inference is supported by laboratory analyses demonstrating that the
external structure of small scatterers can exhibit wavelength-depen-
dent interactions with light41
. As the wavelength begins to exceed
the size of the scatterer, small grains become less opaque, leading to
a relative increase in reflectance. The observed phase reddening thus
implies the presence of micrometre-scale material on the surface. The
presence of fine particles is consistent with one possible interpretation
of the moderate global thermal inertia: a dust coating on boulders.
Reflectance and thermal emission spectra are also consistent with the
presence of fine particulates among the abundant boulders11
.
Cumulativefrequencyperkm2
10,000
1,000
Completenesslimit
100
10
1
100101
Boulder diameter (longest dimension in m)
–2.9 ± 0.3
Fig. 3 | Global cumulative size–frequency distribution of boulders.
Bennu’s global cumulative size–frequency distribution of boulders plotted
in logarithmic space. The data presented here are considered complete
to >8 m (see Methods). Note the break in trend for boulders in the 20- to
40-m-diameter range. There is a deficit of boulders with diameters in
the ranges of 25 to 30 m and 33 to 43 m. Light blue data points represent
individual boulder diameters, while the red line represents the best-fit
power-law slope.
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5. ArticlesNATURE ASTROnOmy
Finally, our thermal analysis finds that Bennu has a rough surface
(root mean square (RMS) slope of 43 ± 1°, Supplementary Fig. 2).
This roughness is comparable to that of other asteroids42–45
but
rougher than that of the Moon46
. The model itself does not set a
spatial scale for this roughness; it can be anywhere between the
resolution of the shape model used for the thermal analysis (~12 m)
and the diurnal thermal skin depth (~2 cm, see Methods), though
we expect that roughness at the smaller length scales dominates the
thermal signature42
. From the shape model of Bennu3
, we find RMS
slopes that increase with decreasing spatial scale. Extrapolation of
a power-law fit to roughness estimates from the shape model at
four spatial scales fits the measured thermal roughness at a spatial
scale of ~2 cm (Supplementary Fig. 7). We therefore predict that the
surface of Bennu is rough at small spatial scales, perhaps consis-
tent with the images of Ryugu returned by the MASCOT lander47
.
Images of the surface of Bennu during the Reconnaissance phase of
the mission will test this prediction.
The presence of micrometre-scale particles on Bennu runs coun-
ter to the expectation that small (>1 km) airless bodies have coarser
regolith because their lower gravity hinders retention of fines (which
escape the surface through impact events, solar wind pressure, and
centripetal forces13,48,49
). However, it is consistent with the findings
of the Hayabusa mission, which collected micrometre-size particles
from the surface of Itokawa50
. The presence of such particles implies
an enhanced ability of the finest material to remain coupled to the
surface through electrostatic effects51
, or the ongoing production of
particles through micrometeorite impacts50
and thermal fatigue of
boulders26
on timescales shorter than the loss mechanisms.
Conclusion and perspectives
Our initial findings from imaging and thermal data reveal a rub-
ble-pile asteroid with extensive surficial diversity. There exists a
heterogeneity of particle sizes on the surface. Large-scale boul-
ders imply the presence of intact materials that originated at or
before the disruption of Bennu’s parent body, whereas evidence of
micrometre-scale particles points to more recent in situ production
and retention of fines on the surface of the asteroid. The thermal
inertia of Bennu suggests either a substantial population of centi-
metre-scale particles among the surface boulders, thin dust cover
blanketing the boulders, high porosity of the boulders, or a com-
bination of these. Despite the inferred range of particle sizes, there
are no large areas of well-sorted particulate regolith. The presence
of bright boulders with a distinct size-frequency distribution may
be primordial—perhaps, exposed fragments of a heterogeneous
parent body that was collisionally disrupted. Conversely, their
presence could be explained as fresher material that has undergone
10 20 30 40 50 60
Boulder diameter (longest dimension in m)
3
4
5
6
7
8
9
10
11
12
Normalalbedo(%)
Global average albedo
Globalcompletenesslimit
Cumulativefrequencyperkm2
10,000
1,000
100
10
1
10010
Averagealbedo
completenesslimit
Brightalbedocompletenesslimit
1
–2.5 ± 0.2
–4.4 ± 0.7
Boulder diameter (longest dimension in m)
a b
Bright albedo (> 6.8%)
Average albedo
Fig. 4 | Albedo trends among Bennu’s boulders. a, Boulders on Bennu: normal albedo versus size. The brightest boulders have smaller diameters. The
completeness limit of the global distribution of boulders and the global average albedo of Bennu are shown for context. b, Bennu’s CSFD of boulders
with average albedo and bright albedo (>6.8%) in logarithmic space. While small numbers influence the power-law index for the bright boulders, these
data suggest that the bright boulders have a different size–frequency distribution than the average-albedo boulders. Light blue data points represent the
individual diameters of bright boulders, and dark blue points represent the individual diameters of average-to-dark boulders. The red lines associated with
each dataset represent their best-fit power-law slope.
10 m
Fig. 5 | Evidence of in situ boulder disaggregation. A boulder that appears
to be degrading into its constituent clasts (approximate coordinates of 45°
latitude, 110° longitude). This image was acquired with PolyCam and has an
average phase angle of 51.33° and a pixel scale of 0.643 m pixel–1
.
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6. Articles NATURE ASTROnOmy
less optical surface modification via space weathering. We will test
these hypotheses with observations at higher spatial and spectral
resolutions planned for the Detailed Survey52
phase of the mission
in the spring of 2019.
Methods
Calibration of OCAMS images. OCAMS images are processed by a calibration
pipeline to be corrected for known sources of noise and converted to physical
units. The corrections include bias and dark subtraction, charge smear removal and
flat fielding. The pipeline removes noise using algorithms and data generated by a
combination of ground-based and in-flight calibrations. The conversion to physical
units is in terms of reflectance (that is, radiance factor or I/F). All image data used
in this analysis are described in terms of reflectance.
The absolute accuracy of the radiometric calibration is set by the in-flight
calibration using images of the Moon taken during the OSIRIS-REx Earth Gravity
Assist (EGA). We compare these images, taken with each of the cameras and with
each of MapCam’s filters, with images taken by the RObotic Lunar Observatory
(ROLO)53
. We use the ROLO bands that most closely match the OCAMS filters:
475 nm for b´, 553 nm for v, 703 nm for w, 865 nm for x and 665 nm for pan. We
scale the ROLO data to match the phase angle of the OCAMS EGA images, ~42°,
using the ROLO photometric model of the lunar surface.
We register the ROLO data to their backplanes and project them into a
common equal-area map and then back-project the data into OCAMS camera
space. Because the ROLO and OCAMS acquired their images with different
illumination conditions, we photometrically correct the ROLO and OCAMS data
with a McEwen model54
. Moreover, because the ROLO and OCAMS images view
different portions of the Moon, we reduce the area of the OCAMS images to match
the ROLO images. We can then directly compare ROLO and OCAMS data by
taking a ratio of the images projected into the same space. This comparison is noisy
due to the imperfect registration between the two images. Therefore, we calculate
a histogram of the image ratio and reduce the dataset to pixels that are within
two standard deviations of the mean. This outlier rejection reduces the noise and
effectively eliminates limb pixels, which have non-physical values after photometric
correction. We take the mean of the remaining pixels to produce the correction to
the OCAMS radiometric calibration.
Global mosaic of Bennu. The global mosaic of Bennu in Fig. 2 was constructed
using calibrated PolyCam images in units of I/F taken on 1 December 2018 over
a full 4.3-h rotational period of Bennu. The images were taken between 05:13:11
and 09:11:41 utc when the spacecraft’s distance to Bennu was between 30.3 and
31.6 km. The corresponding spatial scale of the images was between 0.41 and
0.43 m pixel–1
, while the phase angle of the observation changed between 33.7° and
35.7°. Additional MapCam images from 13 December 2018 were added to fill in
the south pole (–Z). These images were taken between 00:47:30 and 05:04:57 utc.
Spacecraft distance was between 8.93 and 11.09 km. The pixel resolution of the
images was between 1.600 and 1.885 m pixel–1
with phase angles between 39.3°
and 56.2°.
The global mosaic was constructed using the software and methods described
in ref. 55
. No photometric correction was performed before mosaicking. However,
a process similar to the ISIS3 noseam application was applied to minimize the
presence of seams and to improve the cosmetic quality of the mosaic. Finally, some
images were manually placed in areas where the automatic image prioritization
mosaicking scheme yielded imperfect results. All geographic coordinates in this
paper use a 0–360° convention for longitude.
Boulder size-frequency distribution and albedo calculations. OSIRIS-REx
Mission Terminology defines a feature as a boulder if it has positive relief and
a diameter ≥21 cm, a size that is consistent with the diameter of the TAGSAM
annular aperture. In that Mission Terminology, ‘cobbles’ are particles between 2
and 21 cm, and regolith fines are all particles smaller than 2 cm (that is, ingestible
by the sampling mechanism). We use this terminology throughout the paper. For
the purposes of counting a boulder towards the statistical population of particles
on Bennu’s surface, these objects must also have a definable perimeter that is not
partially buried and be characterized by the consistent presence of an elongated
shadow. Accordingly, the partially exposed dark boulder outcrop at (–20° latitude,
30° longitude) is not counted within the size-frequency distribution we report, as
its full extent remains unknown.
Boulders in this dataset were identified across seven PolyCam images taken
on 1 December 2018, covering a full rotational period of Bennu. The images were
taken between 05:13:11 and 09:11:41 utc when the spacecraft’s distance to Bennu
was between 30.3 and 31.6 km. The corresponding spatial scale of these images was
between 0.41 and 0.43 m pixel–1
, while the phase angle of the observation changed
between 33.7° and 35.7°.
Using the geographic information system software ArcMap, boulders were
manually identified in OCAMS images using polylines. The longest axis dimension
was measured; for simplicity we refer to this as boulder diameter. The positions of
polyline geometries are linked to the body-fixed Cartesian coordinates from OCAMS
geometric backplanes, which were calculated using the ISIS3 spiceinit routine and the
v13 shape model of Bennu, with an average facet size of 75 cm (ref. 3
).
The polyline endpoints and the midpoint are recorded and used to calculate
boulder length. This technique allows us to identify boulders on unprojected
images that have not been resampled.
Reflectances for each boulder were extracted from the midpoint of each
polyline to avoid shadowed pixels that often occur at measurement endpoints.
Reflectances were converted to normal albedo using the Lommel–Seeliger disk
function and an exponential phase function (see section ‘Resolved photometric
modelling’) to correct I/F values to 0° phase angle, 0° emission angle, and 0°
incidence angle (0°, 0°, 0°). Boulders with reflectances below 0.03 were not
included in this analysis as manual inspection of several low-reflectance boulders
indicate shadowing. Likewise, boulders identified at incidence or emission angles
≥70° were excluded as reflectance values after photometric correction with a
Lommel–Seeliger disk function may become unphysical as those angles approach
90°. We consider bright boulders to be >6.8% normal albedo, which represents
boulders that exceed 1σ of the mean boulder albedo for the global population of
boulders presented here.
In Fig. 3, we plot the global unbinned CSFD of boulders on Bennu in
logarithmic space. In Fig. 4b, we plot the unbinned cumulative size-frequency
distribution per normal albedo in logarithmic space. For each dataset, we
assume the number of boulders detected follows a Poisson distribution56
. Thus,
measurement uncertainty for individual boulders is captured as the square root of
the number of boulders greater than or equal to D, normalized by surface area. We
use surface area of 0.786 km2
derived from the v13 shape model3
.
Completeness limits used to determine CSFDs were estimated from the data
using a statistical approach to limit individual judgement in the assessment of
data completeness. Specifically, we follow the technique in ref. 57
and applied it
to boulder size-frequency distributions in ref. 58
. Accordingly, completeness is
defined as the smallest value above which the differences between the probability
distributions of the measured data and a best-fit power-law model are minimized.
The distance between both distributions is quantified using the Kolmogorov–
Smirnov statistic. We estimated the uncertainty for each completeness limit by
performing a non-parametric bootstrap. This randomly samples the measurements
with replacement to produce 1,000 synthetic datasets of a similar distribution,
estimating the completeness limit for each, and taking the standard deviation.
For the global population, we estimate a completeness limit of 8.4 ± 1.7 m, for
the bright albedo population, 5.0 ± 0.5 m, and for the average albedo population,
5.1 ± 1.1 m. The difference in the completeness limits between the global boulder
dataset and the datasets per albedo likely indicates that multiple statistically
distinct boulder populations exist at scales <8.4 ± 1.7 m, which cannot be
adequately modelled by a single power-law distribution.
The method of maximum likelihood is used to estimate the power-law
index57,58
. We estimated uncertainty in the power-law index in the same manner as
the completeness limit by performing a non-parametric bootstrap. The resulting
uncertainty value is the standard deviation of the synthetic datasets produced
during the bootstrap. For the global population, we estimate a power-law index
of −2.9 ± 0.3, for the bright albedo population, −4.4 ± 0.7, and for the average
albedo population, −2.5 ± 0.2. The larger uncertainty associated with the bright
10 m
Fig. 6 | Dark diffuse units. The inset shows one of the observed dark
diffuse units on Bennu. Low-albedo (~3.4%) material blankets underlying
terrain with a global average albedo. The central boulder mantled by dark
material is at approximately –65° latitude, 32° longitude. The image has
a phase angle of 4.292° and pixel scale of 3.546 m pixel–1
. This image has
been stretched to highlight units of dark material.
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population of boulders is likely a result of the relatively smaller number of boulders
in this dataset.
Observations and preparation of OTES and OVIRS thermal radiance. The disk-
integrated, rotationally resolved OVIRS data used in the thermal analysis were
obtained on 2 and 3 November 2018. Observations began at 04:12 utc each day.
Exposure times were ~1 s, and spectra were taken continuously for ~4.35 h (slightly
more than one full rotation of Bennu). On 2 November, the spacecraft–Bennu
distance, Bennu heliocentric distance, and phase angle were ~197 km, 1.041 au,
and 5.1°, and Bennu filled ~0.37 of the field of view (FOV). On 3 November, these
values were ~190 km, 1.037 au, 4.5°, and ~0.39. We began our analysis with the L3a
radiometrically corrected OVIRS radiance spectra. The OVIRS spectra of Bennu
are dominated by thermal radiance at λ ≳ 3 μm. We restricted thermal analysis of
OVIRS to λ = 3.5–4.0 μm, where the thermal radiance is ~8 to 25 times the reflected
radiance. To isolate the thermal radiance, we estimated the reflected radiance by
scaling the solar spectrum to each OVIRS measurement at ~2.1 μm and subtracted
this estimate from the total measured radiance (Supplementary Fig. 8). We then
binned the remaining thermal radiance to 1° rotation phase for analysis.
The disk-integrated, rotationally resolved OTES data used in the thermal
analysis were obtained on 8 and 9 November 2018. Observations began at
04:13 utc each day. Exposure times were ~2 s, and spectra were taken continuously
for ~4.49 h. On 8 November, the spacecraft–Bennu distance, Bennu heliocentric
distance, and phase angle were ~162 km, 1.021 au, and 4.5°, and Bennu filled
~0.14 of the FOV. On 3 November, these values were ~159 km, 1.018 au, 5.7°, and
~0.15. Bennu was not perfectly centred in the OTES FOV, and the asymmetric
filling caused calibration complications for this Fourier-transform infrared (FTIR)
spectrometer11
. For the analysis presented here, neither the absolute radiometric
nor the relative spectral calibrations were completed. Analysis of the OTES disk-
integrated Approach phase data was therefore restricted to fitting relative thermal
lightcurves of different wavelength channels independently. As with OVIRS, the
relative thermal flux was binned to 1° rotation phase for analysis.
We also reanalysed previous observations of Bennu by the Spitzer space
telescope using the updated shape and spin state determined by OSIRIS-REx.
Details of the Spitzer data can be found in ref. 12
, and results of the reanalysis
can be found in the Supplementary Information. For analysis of all thermal
data, we used the shape model (v13) determined from stereophotoclinometry
performed on images of Bennu taken with OCAMS3
and the corresponding
spin pole and rotation period (RA = 85.3 ± 0.2°, Dec = −60.2 ± 0.2°, rotation
period = 4.296061 ± 2 × 10−6
h). For thermal analysis, the facet size of the shape
model we used was ~12 m. For topography (including boulders) larger than this
scale, the effects of surface tilts, shadowing, and global self-heating are directly
computed. The effects of roughness from smaller-scale topography, including
smaller boulders, are included using hemispherical craters to simulate that sub-
resolution-element roughness.
Thermal model and data fitting. The thermophysical analysis reported here uses a
custom code that is based on the Advanced Thermophysical Model (ATPM)46,59,60
.
For a given set of input parameters (that is, shape model, rotation period and pole
orientation, illumination and viewing geometry, Bond albedo, emissivity, and
thermal inertia), the ATPM computes the surface temperature distribution of an
asteroid by solving 1D heat conduction with a surface boundary condition that
takes into account direct and multiple-scattered sunlight, and also self-shadowing
and self-heating effects resulting from interfacing surfaces. Rough surface thermal-
infrared beaming (that is, re-radiation of absorbed sunlight back towards the Sun
by small-scale surface roughness) is modelled by adding a fractional coverage of
hemispherical craters to each shape model facet. The model flux is then computed
from the model temperatures by summing the Planck function across facets and
parts of hemispherical craters that were visible to the observer at the time of the
measurements. For the analysis of the thermal data of Bennu, surface temperature
distributions and model fluxes were computed for thermal inertias that ranged
from 0 to 600 J m−2
K−1
s−1/2
in equally spaced steps of 10 J m−2
K−1
s−1/2
. We use
a Bond albedo of 0.016, based on the measured geometric albedo and phase
behaviour, and assume bolometric and spectral emissivities of 0.9. The assumption
of 0.9 for bolometric emissivity is typical of silicate materials at these wavelengths,
and constant spectral emissivity is consistent with the low spectral contrast of
Bennu in the mid-infrared (<2%) measured by OTES11
and laboratory spectra of
carbonaceous meteorites.
To derive the thermal properties of Bennu, the model fluxes were compared
against the measured fluxes by varying the rotation phase (that is, the initial
rotational orientation of Bennu at the start of the flux measurements), thermal
inertia, and surface roughness to find the minimum χ2
fit of the dataset analysed.
The uncertainties of the derived thermal properties were assessed by using a
Monte Carlo bootstrap method43
that produced 100 synthetic test datasets from
the uncertainties of the original dataset (that is, including both the individual
data point uncertainties and the instrument absolute calibration uncertainties).
The minimum χ2
fit was sought for each synthetic dataset, and their best fitting
parameters were then averaged to give a mean and standard deviation of the overall
model fit. We used this Monte Carlo bootstrap method for assessing the final
uncertainties instead of a reduced-χ2
cut-off because it more accurately takes into
account the influence of systematic uncertainties introduced by the instrument
absolute calibration.
Calculation of thermal skin depth and characteristic particle size. The thermal
skin depth is the depth over which the amplitude of the thermal wave decreases by
e−1
and is given by
ρ ω
~
Γ
l
c
2
(1)s
p
where Γ is thermal inertia, cp is heat capacity, ρ is grain density and ω is the rate
of temperature variation—the rotation rate of the asteroid in the case of the
diurnal skin depth. From the measured thermal inertia and uncertainties, and
given the range of heat capacities (500 to 1,100 J kg−1
K−1
) and densities (2,000 to
2,900 kg m−3
), the diurnal skin depth on Bennu is 0.8 to 3.0 cm.
Analytical methods to estimate regolith particle size from thermal inertia on
airless bodies use models of heat conduction across particle contacts and radiation
between particles calibrated through laboratory experiments13,61–63
. The general
method consists of computing the effective regolith thermal conductivity from the
measured thermal inertia, calculating a modelled effective thermal conductivity
as a function of particle size considering both solid conduction and radiation
terms for reasonable ranges of regolith properties and model parameters, then
comparing the measured and modelled effective conductivities to find the particle
size(s) where they agree. We employ the methods of refs. 13,61,62
with calibration of
the parameters ξ and ζ from ref. 64
for a wide range (0.1 to 0.9) of possible regolith
porosities (that is, space between regolith grain, distinct from the boulder porosity
discussed in the main text), in order to examine extremes of resulting particle sizes.
Resulting modelled regolith particle diameters are 0.5 to 4 cm. It is important to
note that these simple analytical methods assume that all regolith particles are the
same size (that is, monodisperse), which is physically unrealistic. These modelled
particle sizes are therefore a thermally characteristic particle size that may not
be the same as the average physical regolith particle diameter. For a power-law
particle size distribution, the thermal flux is dominated by the smaller grains in the
distribution. The estimates here, therefore, should not be taken to suggest that the
regolith does not contain perhaps many larger particles (or boulders).
Resolved photometric modelling. As this paper presents the first results from
preliminary OSIRIS-REx data, we have opted to use empirical photometric
functions due to their simple mathematical form and fewer free parameters than
physically motivated models (such as Hapke, Shkuratov, and so on). When multiple
scattering is not significant (that is, for low-reflectance asteroids), the disk function
and phase function can be separated in functional forms6
. In this work, we choose
to use an exponential phase function and use the Lommel–Seeliger disk function.
The disk behaviour of low-reflectance objects (geometric albedo < 0.2) has been
shown to generally follow a Lommel–Seeliger scattering law6
.
To produce the phase plots shown in the main text, we processed images taken
by MapCam in each of its five filters (b´, v, w, x and pan2
) during two mission
phases. The first were acquired between 29 October and 9 November during
OSIRIS-REx’s Approach phase, during which time Bennu subtended at most
50 pixels across its diameter. These data contribute to the low end of the phase
curve, between 0 and 20°. The second group was acquired during the Equatorial
Pass of the Preliminary Survey phase, between 11 and 15 December. In these data,
Bennu subtended between 400 and 900 pixels in MapCam’s field of view, covering a
range of phase angles from 45° to 90°.
Photometric statistics were calculated for each image individually by treating
Bennu’s surface as a global average. To identify the pixels that will contribute to the
average, we apply a reflectance threshold to the images. This threshold was 0.2 for
the Approach images, where Bennu’s limb was not clearly defined, and 0.001 for
the Preliminary Survey images, where the limb was clear. Both thresholds were set
by inspection to include uniformly illuminated portions of the surface, rejecting
off-limb and terminator pixels. The average of the pixels that pass the appropriate
threshold for a given image is the mean reflectance for that image.
To obtain photometric angles, the images are imported into the United States
Geological Survey’s ISIS3 using the data import program ocams2isis. We attach
observation geometry to each image using kernels from the Spacecraft, Planet,
Instrument, C-matrix, Events (SPICE) Toolkit developed by NASA’s Navigation
and Ancillary Information Facility65
. We also attach the geometry from the v13
shape model to the images. The ISIS3 application phocube produces backplanes
for the images, including phase, incidence and emission angle. We calculate the
average of each of these backplanes to get the mean photometric angles for each
image. A summary of these statistics (mean reflectance, phase, incidence and
emission) are compiled in an Image Photometric Data Information File (IPDIF).
We smooth the data by averaging together images that fall within bins that are 1°
wide in phase angle. The binned data are plotted to produce the reflectance curve
shown in Fig. 1.
We process the unbinned IPDIF with a photometric modelling script, written
in Interactive Data Language (IDL), to fit the data against a Lommel–Seeliger
model. This model includes the Lommel–Seeliger disk function, shown in equation
(2), and an exponential phase function, shown in equation (3)6
. The modelling
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8. Articles NATURE ASTROnOmy
software solves for the free parameters β, γ and δ; the disk function has no
free parameters.
=
+
d i e
i
i e
( , )
cos( )
cos( ) cos( )
(2)
α = β α γ α δ α+ +
f A( ) e * * * (3)LS
2 3
We fit the data from each of the five filters to the model independently, using the
mpfit tool in IDL. However, the variation between them is subtle; for clarity, Fig. 1
depicts the phase curve of the spectral average, with fit parameters of ALS = 0.0265;
β = −3.55 × 10−2
; γ = 3.074 × 10−4
; and δ = −1.889 × 10−6
. Though the fit is generally
good (χ2
~ 3 × 10−5
), we note some extreme ends of the phase angle range (due to
the opposition surge, though minor, at the low phase angles; due to shadowing and
high incidence angles at high phase angles). The exponential phase function used
here does not perfectly capture those nuances, but represents the bulk of the surface
behaviour well.
Geometric albedo is estimated by extrapolating the reflectance phase curves to
0° phase angle. As the exponential phase curve used in our model does not have
a term to account for opposition surge, we perform a linear extrapolation from
0.7–2° to the 0° phase angle as these data show a change in slope that departs from
the best-fit exponential function.
The reflectance ratio in Fig. 1 is calculating by dividing the binned reflectance
data for the b′, w, and x filters by the data from the v filter. We further normalize
the data to the v filter at 0° phase and plot them as a function of phase to illustrate
the reddening that occurs at high phase. Taking the ratio of the data eliminates the
need to track absolute radiometry uncertainty. However, a relative uncertainty of
~0.5% remains due to the sub-spacecraft position and the point in Bennu’s orbit
at which the image data were acquired. These two factors affect Bennu’s apparent
reflectance due to changes in Bennu’s projected area and its albedo variation.
Code availability
The thermophysical analysis reported here uses a custom code that is based on the
Advanced Thermophysical Model (ATPM) of refs. 46,59,60
. The ISIS3 code used to
generate the image processing data products is available from the US Geological
Survey–Astrogeology Science Center: https://isis.astrogeology.usgs.gov/
Data availability
The data that support the plots within this paper and other findings of this study
are available from the corresponding authors upon reasonable request. Raw (L0)
through calibrated (L2, L3) OCAMS, OVIRS and OTES data will be available via
the Planetary Data System (PDS) (https://sbn.psi.edu/pds/resource/orex/). Data
are released to the PDS according to the schedule provided in the OSIRIS-REx
Data Management Plan found in the OSIRIS-REx PDS archive. Image mosaics and
photometric models will be available in the PDS 1 year after departure from the
asteroid.
Received: 31 January 2019; Accepted: 19 February 2019;
Published: xx xx xxxx
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Department of Earth Sciences, University of Toronto, Toronto, Ontario, Canada. 42
Department of Earth, Ocean and Atmospheric Sciences,
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Department of Geography, University of Winnipeg, Winnipeg, Manitoba, Canada.
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Jacobs Technology, Houston, TX, USA. 57
JAXA Institute of Space and Astronautical
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KinetX
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Royal Ontario Museum, Toronto, Ontario, Canada. 73
School of Earth and Planetary Sciences, Curtin University, Perth, Western
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SETI Institute, Mountain View, CA, USA. 75
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Space Systems Laboratory, Department of Aeronautics and Astronautics, Massachusetts Institute
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US Geological Survey Astrogeology Science Center, Flagstaff, AZ, USA. 79
London Stereoscopic Company, London,
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Université de Lorraine, Nancy, France.
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