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.
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.
This document summarizes observations from the occultation of a star by the dwarf planet Eris on November 6, 2010. Observations were made from two sites in Chile and one in Argentina. The occultation data is consistent with Eris having a spherical shape with a radius of 1,163 km and a density of 2.52 g/cm3. No detectable atmosphere was observed, placing an upper limit on surface pressure of 1 nanobar. The observations indicate Eris has a high visible albedo similar to Pluto. The results show Eris to be comparable in size and composition to Pluto.
This document describes the discovery and characterization of CFBDSIR2149, a late T dwarf found to have an unusually red J-K color and enhanced K-band flux. Spectroscopy with X-Shooter revealed it has a T7 spectral type with low surface gravity features, indicating it is a young substellar object. Comparison to atmospheric models suggests it has a temperature of 650-750K, surface gravity of logg=3.75-4.0, and a mass in the planetary regime of 4-7 Jupiter masses. An analysis of its proper motion finds an 87% probability it is a member of the young AB Doradus moving group, which would make it a free-floating planet with an
The harps serach_for_southern_exoplanets_02Sérgio Sacani
The document presents an analysis of additional radial velocity measurements of the M dwarf stars Gl 433 and Gl 667C, obtained with the HARPS spectrograph. It finds:
- For Gl 433, one planet (Gl 433b) with a minimum mass of about 5.5 Earth masses and an orbital period of about 7 days. Longer period radial velocity variations are also detected, likely due to magnetic activity cycles.
- For Gl 667C, two planets are found. Gl 667Cb has a minimum mass of about 5.5 Earth masses and an orbital period of about 7 days. Gl 667Cc has a minimum mass of about 4.25 Earth masses and orbits in the habitable zone of its star with a
This document summarizes an observational study of 92 southern stars using near-infrared interferometry to search for hot exozodiacal dust. The study found an 11% detection rate of bright dust, with 9 confirmed and 3 tentative detections. The detection rate decreased for later spectral type stars and increased with stellar age. No correlation was found between the presence of cold dust and hot dust. Spectral analysis suggested the dust is extremely hot or emission is dominated by scattered light in most cases. The results provide insights into the prevalence and properties of dust near the habitable zones of other stars.
Properties of rubble-pile asteroid (101955) Bennu from OSIRIS-REx imaging and...Sérgio Sacani
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
Discovery of a_probable_4_5_jupiter_mass_exoplanet_to_hd95086_by_direct_imagingSérgio Sacani
The document reports the discovery of a probable 4-5 Jupiter-mass exoplanet orbiting the young star HD 95086. Deep imaging observations using VLT/NaCo detected a faint source at a separation of 56 AU from the star. Follow-up observations over more than a year found the source to be co-moving with the star, suggesting it is bound. Its luminosity corresponds to a predicted mass of 4-5 Jupiter masses, making it the lowest mass exoplanet directly imaged around a star. If confirmed, this discovery could provide insights into giant planet formation and evolution.
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.
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.
This document summarizes observations from the occultation of a star by the dwarf planet Eris on November 6, 2010. Observations were made from two sites in Chile and one in Argentina. The occultation data is consistent with Eris having a spherical shape with a radius of 1,163 km and a density of 2.52 g/cm3. No detectable atmosphere was observed, placing an upper limit on surface pressure of 1 nanobar. The observations indicate Eris has a high visible albedo similar to Pluto. The results show Eris to be comparable in size and composition to Pluto.
This document describes the discovery and characterization of CFBDSIR2149, a late T dwarf found to have an unusually red J-K color and enhanced K-band flux. Spectroscopy with X-Shooter revealed it has a T7 spectral type with low surface gravity features, indicating it is a young substellar object. Comparison to atmospheric models suggests it has a temperature of 650-750K, surface gravity of logg=3.75-4.0, and a mass in the planetary regime of 4-7 Jupiter masses. An analysis of its proper motion finds an 87% probability it is a member of the young AB Doradus moving group, which would make it a free-floating planet with an
The harps serach_for_southern_exoplanets_02Sérgio Sacani
The document presents an analysis of additional radial velocity measurements of the M dwarf stars Gl 433 and Gl 667C, obtained with the HARPS spectrograph. It finds:
- For Gl 433, one planet (Gl 433b) with a minimum mass of about 5.5 Earth masses and an orbital period of about 7 days. Longer period radial velocity variations are also detected, likely due to magnetic activity cycles.
- For Gl 667C, two planets are found. Gl 667Cb has a minimum mass of about 5.5 Earth masses and an orbital period of about 7 days. Gl 667Cc has a minimum mass of about 4.25 Earth masses and orbits in the habitable zone of its star with a
This document summarizes an observational study of 92 southern stars using near-infrared interferometry to search for hot exozodiacal dust. The study found an 11% detection rate of bright dust, with 9 confirmed and 3 tentative detections. The detection rate decreased for later spectral type stars and increased with stellar age. No correlation was found between the presence of cold dust and hot dust. Spectral analysis suggested the dust is extremely hot or emission is dominated by scattered light in most cases. The results provide insights into the prevalence and properties of dust near the habitable zones of other stars.
Properties of rubble-pile asteroid (101955) Bennu from OSIRIS-REx imaging and...Sérgio Sacani
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
Discovery of a_probable_4_5_jupiter_mass_exoplanet_to_hd95086_by_direct_imagingSérgio Sacani
The document reports the discovery of a probable 4-5 Jupiter-mass exoplanet orbiting the young star HD 95086. Deep imaging observations using VLT/NaCo detected a faint source at a separation of 56 AU from the star. Follow-up observations over more than a year found the source to be co-moving with the star, suggesting it is bound. Its luminosity corresponds to a predicted mass of 4-5 Jupiter masses, making it the lowest mass exoplanet directly imaged around a star. If confirmed, this discovery could provide insights into giant planet formation and evolution.
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.
This document summarizes observations of the debris disk around the subgiant star κ CrB using Herschel and Keck. Herschel spatially resolved images of the debris disk, the first such images of a disk around a subgiant star. Keck radial velocity monitoring provided evidence for a second planetary companion around κ CrB. Keck adaptive optics imaging placed an upper limit on the mass of this companion. Modeling of the Herschel images showed the dust is broadly distributed but could not distinguish between a single wide belt or two narrow belts. The observations are consistent with dynamical depletion or collisional erosion clearing the inner regions of the disk.
The neowise discovered_comet_population_and_the_co_co2_production_ratesSérgio Sacani
Após o seu lançamento em 2009, a sonda NEOWISE da NASA já observou 163 cometas durante a missão primária WISE/NEOWISE. Essa amostra do telescópio espacial representa a maior pesquisa infravermelha de cometas já feitas até o momento. Os dados dessa pesquisa estão dando uma nova ideia sobre a poeira, o tamanho dos núcleos do cometa, e a taxa de produção dos gases difíceis de serem observados como dióxido de carbono e monóxido de carbono. Os resultados do censo do NEOWISE dos cometas foram recentemente publicados no Astrophysical Journal.
O monóxido de carbono (CO) e o dióxido de carbono (CO2) são moléculas comuns encontradas no ambiente do início do Sistema Solar, e nos cometas. Na maior parte das circunstâncias, a sublimação do gelo de água provavelmente guia a atividade nos cometas quando eles chegam perto do Sol, mas em distâncias maiores e em temperaturas mais frias, outras moléculas como o CO e o CO2 podem ser os principais guias. O dióxido e o monóxido de carbono são moléculas difíceis de serem detectadas da terra, devido a abundância dessas moléculas na própria atmosfera terrestre que podem obscurecer o sinal. A sonda NEOWISE vaga além da atmosfera da Terra, fazendo essas medidas dos gases emitidos pelos cometas possíveis.
“Essa é a primeira vez que nós observamos essa grande evidência estatística do monóxido de carbono obtida enquanto o gás do cometa é emitido quando ele está mais distante do Sol”, disse James Bauer, vice-principal pesquisador da missão NEOWISE do Laboratório de Propulsão a Jato da NASA em Pasadena, na Califórnia, e autor do artigo. “Emitindo o que é provavelmente monóxido de carbono além de 4 Unidades Astronômicas, ou seja, 600 milhões de quilômetros, isso nos mostra que os cometas podem ter guardado a maior parte dos gases quando eles se formaram, e ficaram ali guardados por bilhões de anos. A maioria dos cometas que nós observamos ativos além das 4 Unidades Astronômicas, são cometas de períodos longos, cometas com períodos orbitais maiores que 200 anos que gastam a maior parte da sua vida além da órbita de Netuno”.
1. Scientists used stellar occultation to measure the size of the dwarf planet Eris more accurately. They found it has a radius of 1,163 km, smaller than previous estimates, though not definitively smaller than Pluto due to uncertainties in Pluto's size.
2. Surprisingly, Eris' surface was found to be very bright, which could indicate a collapsed or localized atmosphere had recently condensed onto the surface from sublimated ices as Eris moves closer to the Sun in its orbit.
3. The discovery of Eris and other large Kuiper Belt objects has challenged definitions of planets and our understanding of the outer solar system, showing Pluto is not unique and sparking debate about what constitutes
This document reports on observations of comet 103P/Hartley 2 made by the WISE space telescope in May 2010 and additional ground-based telescopes. The WISE observations detected the comet's coma, nucleus, and dust trail. Analysis of the coma suggests dust particles larger than those observed for comet 81P/Wild 2. The extracted nucleus is estimated to be 0.6 km in radius. Emission detected at 4.6 microns may be from carbon monoxide or carbon dioxide gas. Carbon dioxide production rates are estimated to be 3.5×1024 molecules per second. The dust trail was detected with an optical depth of 9×10-10 and minimum mass of 4×1010 kg. These observations provide
The x-ray diffraction analysis of soil samples from Rocknest at Gale Crater on Mars revealed:
1) Crystalline components including plagioclase, olivine, augite, pigeonite, and minor amounts of other phases.
2) 27±14% of the soil was amorphous material, likely containing multiple iron-bearing and volatile phases including possibly hisingerite.
3) The crystalline components are similar to martian basalts and meteorites, while the amorphous component is similar to soils on Earth like those on Mauna Kea, Hawaii.
Herschel space telescope observations reveal cold dust emitting from Supernova 1987A at a temperature of 17-23 K, indicating a dust mass of 0.4-0.7 solar masses. The dust must originate from the supernova ejecta, requiring efficient precipitation of refractory elements into dust. This implies that supernovae can produce the large dust masses seen in early galaxies.
This document summarizes a study that identified 195 compact elliptical galaxies across different environments using data from optical and ultraviolet sky surveys. The researchers constructed the sample by selecting galaxies that were outliers from the universal color-magnitude relation and had small sizes and high stellar velocity dispersions based on spectral modeling. They found that 7 of the galaxies were isolated, not belonging to any known galaxy groups. For these isolated galaxies, the researchers identified possible host galaxies located up to 3.3 Mpc away. The stellar populations of the isolated compact elliptical galaxies were found to be similar to those in galaxy groups and clusters, suggesting a common formation mechanism.
Cosmogenic Nuclide Dating Of Sahelanthropus Tchadensis And Australopiethcus B...Kristian Pedersen
This study used cosmogenic nuclide dating to determine the ages of sedimentary units containing hominid remains at two localities in Chad - KT 12 locality in Koro Toro and TM 266 locality in Toros-Menalla. At KT 12, which contained Australopithecus bahrelghazali, authigenic 10Be/9Be dating of the sedimentary level yielded an age of 3.58 ± 0.27 Ma, consistent with an early Pliocene age estimation. At TM 266, where Sahelanthropus tchadensis was found, 28 10Be/9Be ages from the anthracotheriid unit containing the hominid remains bracketed its age between 6.8
A super earth transiting a naked-eye starSérgio Sacani
This document summarizes the detection of transits of an exoplanet orbiting the star 55 Cnc, using photometry from the MOST space telescope. The transits match the period, phase, duration, and depth predicted for the innermost planet of 55 Cnc, designated 55 Cnc e. Analysis of the transit data indicates the planet has a mass of 8.57 Earth masses, a radius of 1.63 Earth radii, and a dense composition of rock and iron. This makes 55 Cnc e similar to other dense super-Earth exoplanets in short orbits, unlike lower-density super-Earths further from their stars. The brightness of 55 Cnc will enable further study of this transiting exoplanet system.
The petrochemistry of_jake_m_a_martian_mugeariteSérgio Sacani
The rock "Jake_M" was the first rock analyzed by Curiosity on Mars. It has a distinct chemical composition compared to other known Martian rocks. Jake_M has a basaltic composition but is alkaline, with over 15% normative nepheline content. Its chemical makeup is similar to terrestrial mugearites, fractionated alkaline rocks found at ocean islands and rifts. This suggests Jake_M formed through extensive fractional crystallization of an alkaline magma at elevated pressure, possibly with water. The discovery of an alkaline rock expands the diversity of known Martian igneous compositions.
The harps n-rocky_planet_search_hd219134b_transiting_rocky_planetSérgio Sacani
Usando o espectrógrafo HARPS-N acoplado ao Telescopio Nazionale Galileo no Observatório de Roque de Los Muchachos, nas Ilhas Canárias, os astrônomos descobriram três exoplanetas, classificados como Super-Terras e um gigante gasoso orbitando uma estrela próxima, chamada de HD 219134.
A HD 219134, também conhecida como HR 8832 é uma estrela do tipo anã-K de quinta magnitude, localizada a aproximadamente 21 anos-luz de distância da Terra, na constelação de Cassiopeia.
A estrela é levemente mais fria e menos massiva que o nosso sol. Ela é tão brilhante que pode ser observada a olho nu.
O sistema planetário HD 219134, abriga um planeta gigante gasoso externo e três planetas internos classificados como super-Terras, um dos quais transita em frente à estrela.
Curiosity at gale_crater_characterization_and_analysis_of_the_rocknest_sand_s...Sérgio Sacani
The Rocknest sand shadow analyzed by the Curiosity rover on Mars was similar to coarse-grained ripples analyzed by previous rovers. It consisted of an upper layer of very coarse sand grains armoring the surface, underlain by finer grains. Analysis found the sand was around 55% crystalline material of basaltic composition and 45% amorphous iron-rich glass. This amorphous component contained the volatiles detected and was similar to soils analyzed at other Mars sites, implying the materials were locally derived from similar basaltic sources globally on Mars.
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.
“A ring system detected around the Centaur (10199) Chariklo”GOASA
- The Centaur object (10199) Chariklo was observed to occult a star, revealing the presence of two narrow rings around the object.
- The rings have widths of about 7 km and 3 km, and orbital radii of 391 km and 405 km from the center of Chariklo.
- Evidence supports the rings being composed of water ice and their geometry explaining the dimming and changing spectrum of Chariklo observed between 1997 and 2008. The discovery of rings around a minor planet is a first for the Solar System.
The 19 Feb. 2016 Outburst of Comet 67P/CG: An ESA Rosetta Multi-Instrument StudySérgio Sacani
On 19 Feb. 2016 nine Rosetta instruments serendipitously observed an outburst of gas and dust
from the nucleus of comet 67P/Churyumov-Gerasimenko. Among these instruments were cameras
and spectrometers ranging from UV over visible to microwave wavelengths, in-situ gas, dust and
plasma instruments, and one dust collector. At 9:40 a dust cloud developed at the edge of an image
in the shadowed region of the nucleus. Over the next two hours the instruments recorded a signature
of the outburst that signicantly exceeded the background. The enhancement ranged from 50% of
the neutral gas density at Rosetta to factors >100 of the brightness of the coma near the nucleus.
Dust related phenomena (dust counts or brightness due to illuminated dust) showed the strongest
enhancements (factors >10). However, even the electron density at Rosetta increased by a factor 3
and consequently the spacecraft potential changed from 16V to 20V during the outburst. A
clear sequence of events was observed at the distance of Rosetta (34 km from the nucleus): within 15
minutes the Star Tracker camera detected fast particles ( 25 ms 1) while 100 m radius particles
were detected by the GIADA dust instrument 1 hour later at a speed of 6 ms 1. The slowest
were individual mm to cm sized grains observed by the OSIRIS cameras. Although the outburst
originated just outside the FOV of the instruments, the source region and the magnitude of the
outburst could be determined.
This document introduces the VLT-FLAMES Tarantula Survey, which obtained multi-epoch optical spectroscopy of over 800 massive stars in the 30 Doradus region of the Large Magellanic Cloud. The survey aims to detect massive binary systems through variations in radial velocities and to characterize the properties of O- and B-type stars, addressing questions about stellar and cluster evolution. Spectral classifications are provided for newly discovered emission-line stars, including a new Wolf-Rayet star. The survey data and reduction procedures are overviewed, and upcoming analyses of the massive star properties are announced.
The nonmagnetic nucleus_of_comet_67_p_churyumov_gerasimenkoSérgio Sacani
Artigo descreve como a sonda Rosetta e o módulo Philae descobriram que o cometa Churyumov-Gerasimenko não é magnetizado, contrariando uma teoria da formação do Sistema Solar.
This document summarizes a 1.3 mm continuum survey of protoplanetary disks in the 2-3 Myr old IC348 star cluster using the Submillimeter Array. 10 disks out of 85 young stars were detected with masses ranging from 2-6 Jupiter masses. This distribution is shifted to lower masses by a factor of 20 compared to younger regions like Taurus and Ophiuchus. The results reveal a rapid decline in the number of small dust grains in disks after 1 Myr, likely due to grain growth. The few detected disks may be the best candidates in IC348 to study planet formation.
The morphological diversity_of_comet_67_p_churyumov_gerasimenkoSérgio Sacani
Artigo descreve em detalhes as unidades morfológicas do cometa Churyumov-Gerasimenko, classificadas pelos cientistas com as análises feitas nas imagens de alta resolução da sonda Rosetta da ESA.
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
This document summarizes observations of the debris disk around the subgiant star κ CrB using Herschel and Keck. Herschel spatially resolved images of the debris disk, the first such images of a disk around a subgiant star. Keck radial velocity monitoring provided evidence for a second planetary companion around κ CrB. Keck adaptive optics imaging placed an upper limit on the mass of this companion. Modeling of the Herschel images showed the dust is broadly distributed but could not distinguish between a single wide belt or two narrow belts. The observations are consistent with dynamical depletion or collisional erosion clearing the inner regions of the disk.
The neowise discovered_comet_population_and_the_co_co2_production_ratesSérgio Sacani
Após o seu lançamento em 2009, a sonda NEOWISE da NASA já observou 163 cometas durante a missão primária WISE/NEOWISE. Essa amostra do telescópio espacial representa a maior pesquisa infravermelha de cometas já feitas até o momento. Os dados dessa pesquisa estão dando uma nova ideia sobre a poeira, o tamanho dos núcleos do cometa, e a taxa de produção dos gases difíceis de serem observados como dióxido de carbono e monóxido de carbono. Os resultados do censo do NEOWISE dos cometas foram recentemente publicados no Astrophysical Journal.
O monóxido de carbono (CO) e o dióxido de carbono (CO2) são moléculas comuns encontradas no ambiente do início do Sistema Solar, e nos cometas. Na maior parte das circunstâncias, a sublimação do gelo de água provavelmente guia a atividade nos cometas quando eles chegam perto do Sol, mas em distâncias maiores e em temperaturas mais frias, outras moléculas como o CO e o CO2 podem ser os principais guias. O dióxido e o monóxido de carbono são moléculas difíceis de serem detectadas da terra, devido a abundância dessas moléculas na própria atmosfera terrestre que podem obscurecer o sinal. A sonda NEOWISE vaga além da atmosfera da Terra, fazendo essas medidas dos gases emitidos pelos cometas possíveis.
“Essa é a primeira vez que nós observamos essa grande evidência estatística do monóxido de carbono obtida enquanto o gás do cometa é emitido quando ele está mais distante do Sol”, disse James Bauer, vice-principal pesquisador da missão NEOWISE do Laboratório de Propulsão a Jato da NASA em Pasadena, na Califórnia, e autor do artigo. “Emitindo o que é provavelmente monóxido de carbono além de 4 Unidades Astronômicas, ou seja, 600 milhões de quilômetros, isso nos mostra que os cometas podem ter guardado a maior parte dos gases quando eles se formaram, e ficaram ali guardados por bilhões de anos. A maioria dos cometas que nós observamos ativos além das 4 Unidades Astronômicas, são cometas de períodos longos, cometas com períodos orbitais maiores que 200 anos que gastam a maior parte da sua vida além da órbita de Netuno”.
1. Scientists used stellar occultation to measure the size of the dwarf planet Eris more accurately. They found it has a radius of 1,163 km, smaller than previous estimates, though not definitively smaller than Pluto due to uncertainties in Pluto's size.
2. Surprisingly, Eris' surface was found to be very bright, which could indicate a collapsed or localized atmosphere had recently condensed onto the surface from sublimated ices as Eris moves closer to the Sun in its orbit.
3. The discovery of Eris and other large Kuiper Belt objects has challenged definitions of planets and our understanding of the outer solar system, showing Pluto is not unique and sparking debate about what constitutes
This document reports on observations of comet 103P/Hartley 2 made by the WISE space telescope in May 2010 and additional ground-based telescopes. The WISE observations detected the comet's coma, nucleus, and dust trail. Analysis of the coma suggests dust particles larger than those observed for comet 81P/Wild 2. The extracted nucleus is estimated to be 0.6 km in radius. Emission detected at 4.6 microns may be from carbon monoxide or carbon dioxide gas. Carbon dioxide production rates are estimated to be 3.5×1024 molecules per second. The dust trail was detected with an optical depth of 9×10-10 and minimum mass of 4×1010 kg. These observations provide
The x-ray diffraction analysis of soil samples from Rocknest at Gale Crater on Mars revealed:
1) Crystalline components including plagioclase, olivine, augite, pigeonite, and minor amounts of other phases.
2) 27±14% of the soil was amorphous material, likely containing multiple iron-bearing and volatile phases including possibly hisingerite.
3) The crystalline components are similar to martian basalts and meteorites, while the amorphous component is similar to soils on Earth like those on Mauna Kea, Hawaii.
Herschel space telescope observations reveal cold dust emitting from Supernova 1987A at a temperature of 17-23 K, indicating a dust mass of 0.4-0.7 solar masses. The dust must originate from the supernova ejecta, requiring efficient precipitation of refractory elements into dust. This implies that supernovae can produce the large dust masses seen in early galaxies.
This document summarizes a study that identified 195 compact elliptical galaxies across different environments using data from optical and ultraviolet sky surveys. The researchers constructed the sample by selecting galaxies that were outliers from the universal color-magnitude relation and had small sizes and high stellar velocity dispersions based on spectral modeling. They found that 7 of the galaxies were isolated, not belonging to any known galaxy groups. For these isolated galaxies, the researchers identified possible host galaxies located up to 3.3 Mpc away. The stellar populations of the isolated compact elliptical galaxies were found to be similar to those in galaxy groups and clusters, suggesting a common formation mechanism.
Cosmogenic Nuclide Dating Of Sahelanthropus Tchadensis And Australopiethcus B...Kristian Pedersen
This study used cosmogenic nuclide dating to determine the ages of sedimentary units containing hominid remains at two localities in Chad - KT 12 locality in Koro Toro and TM 266 locality in Toros-Menalla. At KT 12, which contained Australopithecus bahrelghazali, authigenic 10Be/9Be dating of the sedimentary level yielded an age of 3.58 ± 0.27 Ma, consistent with an early Pliocene age estimation. At TM 266, where Sahelanthropus tchadensis was found, 28 10Be/9Be ages from the anthracotheriid unit containing the hominid remains bracketed its age between 6.8
A super earth transiting a naked-eye starSérgio Sacani
This document summarizes the detection of transits of an exoplanet orbiting the star 55 Cnc, using photometry from the MOST space telescope. The transits match the period, phase, duration, and depth predicted for the innermost planet of 55 Cnc, designated 55 Cnc e. Analysis of the transit data indicates the planet has a mass of 8.57 Earth masses, a radius of 1.63 Earth radii, and a dense composition of rock and iron. This makes 55 Cnc e similar to other dense super-Earth exoplanets in short orbits, unlike lower-density super-Earths further from their stars. The brightness of 55 Cnc will enable further study of this transiting exoplanet system.
The petrochemistry of_jake_m_a_martian_mugeariteSérgio Sacani
The rock "Jake_M" was the first rock analyzed by Curiosity on Mars. It has a distinct chemical composition compared to other known Martian rocks. Jake_M has a basaltic composition but is alkaline, with over 15% normative nepheline content. Its chemical makeup is similar to terrestrial mugearites, fractionated alkaline rocks found at ocean islands and rifts. This suggests Jake_M formed through extensive fractional crystallization of an alkaline magma at elevated pressure, possibly with water. The discovery of an alkaline rock expands the diversity of known Martian igneous compositions.
The harps n-rocky_planet_search_hd219134b_transiting_rocky_planetSérgio Sacani
Usando o espectrógrafo HARPS-N acoplado ao Telescopio Nazionale Galileo no Observatório de Roque de Los Muchachos, nas Ilhas Canárias, os astrônomos descobriram três exoplanetas, classificados como Super-Terras e um gigante gasoso orbitando uma estrela próxima, chamada de HD 219134.
A HD 219134, também conhecida como HR 8832 é uma estrela do tipo anã-K de quinta magnitude, localizada a aproximadamente 21 anos-luz de distância da Terra, na constelação de Cassiopeia.
A estrela é levemente mais fria e menos massiva que o nosso sol. Ela é tão brilhante que pode ser observada a olho nu.
O sistema planetário HD 219134, abriga um planeta gigante gasoso externo e três planetas internos classificados como super-Terras, um dos quais transita em frente à estrela.
Curiosity at gale_crater_characterization_and_analysis_of_the_rocknest_sand_s...Sérgio Sacani
The Rocknest sand shadow analyzed by the Curiosity rover on Mars was similar to coarse-grained ripples analyzed by previous rovers. It consisted of an upper layer of very coarse sand grains armoring the surface, underlain by finer grains. Analysis found the sand was around 55% crystalline material of basaltic composition and 45% amorphous iron-rich glass. This amorphous component contained the volatiles detected and was similar to soils analyzed at other Mars sites, implying the materials were locally derived from similar basaltic sources globally on Mars.
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.
“A ring system detected around the Centaur (10199) Chariklo”GOASA
- The Centaur object (10199) Chariklo was observed to occult a star, revealing the presence of two narrow rings around the object.
- The rings have widths of about 7 km and 3 km, and orbital radii of 391 km and 405 km from the center of Chariklo.
- Evidence supports the rings being composed of water ice and their geometry explaining the dimming and changing spectrum of Chariklo observed between 1997 and 2008. The discovery of rings around a minor planet is a first for the Solar System.
The 19 Feb. 2016 Outburst of Comet 67P/CG: An ESA Rosetta Multi-Instrument StudySérgio Sacani
On 19 Feb. 2016 nine Rosetta instruments serendipitously observed an outburst of gas and dust
from the nucleus of comet 67P/Churyumov-Gerasimenko. Among these instruments were cameras
and spectrometers ranging from UV over visible to microwave wavelengths, in-situ gas, dust and
plasma instruments, and one dust collector. At 9:40 a dust cloud developed at the edge of an image
in the shadowed region of the nucleus. Over the next two hours the instruments recorded a signature
of the outburst that signicantly exceeded the background. The enhancement ranged from 50% of
the neutral gas density at Rosetta to factors >100 of the brightness of the coma near the nucleus.
Dust related phenomena (dust counts or brightness due to illuminated dust) showed the strongest
enhancements (factors >10). However, even the electron density at Rosetta increased by a factor 3
and consequently the spacecraft potential changed from 16V to 20V during the outburst. A
clear sequence of events was observed at the distance of Rosetta (34 km from the nucleus): within 15
minutes the Star Tracker camera detected fast particles ( 25 ms 1) while 100 m radius particles
were detected by the GIADA dust instrument 1 hour later at a speed of 6 ms 1. The slowest
were individual mm to cm sized grains observed by the OSIRIS cameras. Although the outburst
originated just outside the FOV of the instruments, the source region and the magnitude of the
outburst could be determined.
This document introduces the VLT-FLAMES Tarantula Survey, which obtained multi-epoch optical spectroscopy of over 800 massive stars in the 30 Doradus region of the Large Magellanic Cloud. The survey aims to detect massive binary systems through variations in radial velocities and to characterize the properties of O- and B-type stars, addressing questions about stellar and cluster evolution. Spectral classifications are provided for newly discovered emission-line stars, including a new Wolf-Rayet star. The survey data and reduction procedures are overviewed, and upcoming analyses of the massive star properties are announced.
The nonmagnetic nucleus_of_comet_67_p_churyumov_gerasimenkoSérgio Sacani
Artigo descreve como a sonda Rosetta e o módulo Philae descobriram que o cometa Churyumov-Gerasimenko não é magnetizado, contrariando uma teoria da formação do Sistema Solar.
This document summarizes a 1.3 mm continuum survey of protoplanetary disks in the 2-3 Myr old IC348 star cluster using the Submillimeter Array. 10 disks out of 85 young stars were detected with masses ranging from 2-6 Jupiter masses. This distribution is shifted to lower masses by a factor of 20 compared to younger regions like Taurus and Ophiuchus. The results reveal a rapid decline in the number of small dust grains in disks after 1 Myr, likely due to grain growth. The few detected disks may be the best candidates in IC348 to study planet formation.
The morphological diversity_of_comet_67_p_churyumov_gerasimenkoSérgio Sacani
Artigo descreve em detalhes as unidades morfológicas do cometa Churyumov-Gerasimenko, classificadas pelos cientistas com as análises feitas nas imagens de alta resolução da sonda Rosetta da ESA.
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
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
No global pluto_like_atmosphere_on_dwarf_planet_makemake_from_a_stellar_occul...Sérgio Sacani
1. A stellar occultation event was observed involving the dwarf planet Makemake on April 23, 2011 using multiple telescopes.
2. Analysis of the light curves from the event showed abrupt disappearances and reappearances of the star, indicating Makemake has no global atmosphere at an upper limit of 4-12 nanobar surface pressure.
3. The occultation data was used to determine Makemake has dimensions of 1,430±9 km by 1,502±45 km, implying a high geometric albedo of 0.77±0.03. This rules out a low density and suggests Makemake is in hydrostatic equilibrium as an oblate spheroid.
Galaxy growth in a massive halo in the first billion years of cosmic historySérgio Sacani
According to the current understanding of cosmic structure formation, the precursors of the most massive structures in the Universe began to form shortly after the Big Bang, in regions corresponding to the largest fluctuations in the cosmic density field1–3. Observing these structures during their period of active growth and assembly—the first few hundred million years of the Universe—is challenging because it requires surveys that are sensitive enough to detect the distant galaxies that act as signposts for these structures and wide enough to capture the rarest objects. As a result, very few such objects have been detected so far4,5. Here we report observations of a far-infrared-luminous object at redshift 6.900 (less than 800 million years after the Big Bang) that was discovered in a wide-field survey6. High-resolution imaging shows it to be a pair of extremely massive star-forming galaxies. The larger is forming stars at a rate of 2,900 solar masses per year, contains 270 billion solar masses of gas and 2.5 billion solar masses of dust, and is more massive than any other known object at a redshift of more than 6. Its rapid star formation is probably triggered by its companion galaxy at a projected separation of 8 kiloparsecs. This merging companion hosts 35 billion solar masses of stars and has a star-formation rate of 540 solar masses per year, but has an order of magnitude less gas and dust than its neighbour and physical conditions akin to those observed in lower-metallicity galaxies in the nearby Universe7. These objects suggest the presence of a dark-matter halo with a mass of more than 100 billion solar masses, making it among the rarest dark-matter haloes that should exist in the Universe at this epoch.
An excess of massive stars in the local 30 Doradus starburstSérgio Sacani
The 30 Doradus star-forming region in the Large Magellanic Cloud is a nearby analog of large
star-formation events in the distant universe.We determined the recent formation history and
the initial mass function (IMF) of massive stars in 30 Doradus on the basis of spectroscopic
observations of 247 stars more massive than 15 solarmasses (M⊙).Themain episode of massive
star formation began about 8 million years (My) ago, and the star-formation rate seems to
have declined in the last 1 My.The IMF is densely sampled up to 200M⊙ and contains 32 ± 12%
more stars above 30 M⊙ than predicted by a standard Salpeter IMF. In the mass range of 15
to 200M⊙, the IMF power-law exponent is 1:90þ0:37
0:26, shallower than the Salpeter value of 2.35.
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.
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.
Detection and characterisation of icy cavities on the nucleus of comet 67P/Ch...Sérgio Sacani
We report on the detection of three icy cavities on the nucleus of comet 67P/Churyumov-Gerasimenko. They were identified on
high-resolution anaglyphs built from images acquired by the OSIRIS instrument aboard the Rosetta spacecraft on 2016 April
9-10. Visually, they appear as bright patches of typically 15 to 30 m across whose large reflectances and spectral slopes in
the visible substantiate the presence of sub-surface water ice. Using a new high-resolution photogrammetric shape model, we
determined the three-dimensional shape of these cavities whose depth ranges from 20 to 47 m. Spectral slopes were interpreted
with models combining water ice and refractory dark material and the water ice abundances in the cavities were found to amount
to a few per cent. The determination of the lifetime of the icy cavities was strongly biased by the availability of appropriate and
favourable observations, but we found evidences of values of up to two years. The icy cavities were found to be connected to jets
well documented in past studies. A thermal model allowed us to track their solar insolation over a large part of the orbit of the
comet and a transitory bright jet on 2015 July 18 was unambiguously linked to the brief illumination of the icy bottom of one of
the cavities. These cavities are likely to be the first potential subsurface access points detected on a cometary nucleus and their
lifetimes suggest that they reveal pristine sub-surface icy layers or pockets rather than recently recondensed water vapor.
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.
This document summarizes the discovery of seven temperate terrestrial planets orbiting the nearby ultracool dwarf star TRAPPIST-1. Through extensive photometric monitoring from both ground-based telescopes and the Spitzer Space Telescope, the researchers detected multiple transiting planets with orbital periods between 1.5 and 12.3 days. Analysis of the transit light curves revealed four additional planets (TRAPPIST-1d, e, f, and g), in addition to the three initially reported. Dynamical modeling suggests the six inner planets have rocky compositions and near-resonant orbits, indicating they likely migrated inward over time. The seven planets have equilibrium temperatures low enough to possibly support liquid water on their surfaces.
Seven temperate terrestrial planets around the nearby ultracool dwarf star TR...Sérgio Sacani
One aim of modern astronomy is to detect temperate, Earth-like
exoplanets that are well suited for atmospheric characterization.
Recently, three Earth-sized planets were detected that transit (that
is, pass in front of) a star with a mass just eight per cent that of
the Sun, located 12 parsecs away1. The transiting configuration of
these planets, combined with the Jupiter-like size of their host star—
named TRAPPIST-1—makes possible in-depth studies of their
atmospheric properties with present-day and future astronomical
facilities1–3. Here we report the results of a photometric monitoring
campaign of that star from the ground and space. Our observations
reveal that at least seven planets with sizes and masses similar
to those of Earth revolve around TRAPPIST-1. The six inner
planets form a near-resonant chain, such that their orbital periods
(1.51, 2.42, 4.04, 6.06, 9.1 and 12.35 days) are near-ratios of small
integers. This architecture suggests that the planets formed farther
from the star and migrated inwards4,5. Moreover, the seven planets
have equilibrium temperatures low enough to make possible the
presence of liquid water on their surfaces6–8.
A dust obscured_massive_maximum_starburst_galaxy_at_a_redshift_634Sérgio Sacani
This document summarizes the discovery of a massive, intensely star-forming galaxy located at a redshift of 6.34, approximately 880 million years after the Big Bang. Observations revealed a suite of molecular and atomic emission and absorption lines that unambiguously determined the galaxy's redshift. Analysis shows the galaxy contains over 100 billion solar masses of chemically evolved interstellar medium, constituting at least 40% of its baryonic mass. It is forming new stars at a rate over 2,000 times that of the Milky Way, making it a "maximum starburst" galaxy. Despite an overall decline in cosmic star formation at the highest redshifts, this discovery shows that environments capable of hosting the most massive starbursts existed very early
Neptune-sized planets exhibit a wide range of compositions and densities,
depending on factors related to their formation and evolution history, such as
the distance from their host stars and atmospheric escape processes. They can vary
from relatively low-density planets with thick hydrogen–helium atmospheres1,2
to
higher-density planets with a substantial amount of water or a rocky interior with a
thinner atmosphere, such as HD 95338 b (ref. 3), TOI-849 b (ref. 4) and TOI-2196 b
(ref. 5). The discovery of exoplanets in the hot-Neptune desert6
, a region close to
the host stars with a defcit of Neptune-sized planets, provides insights into the
formation and evolution of planetary systems, including the existence of this region
itself. Here we show observations of the transiting planet TOI-1853 b, which has a
radius of 3.46 ± 0.08 Earth radii and orbits a dwarf star every 1.24 days. This planet
has a mass of 73.2 ± 2.7 Earth masses, almost twice that of any other Neptune-sized
planet known so far, and a density of 9.7 ± 0.8 grams per cubic centimetre. These
values place TOI-1853 b in the middle of the Neptunian desert and imply that heavy
elements dominate its mass. The properties of TOI-1853 b present a puzzle for
conventional theories of planetary formation and evolution, and could be the result
of several proto-planet collisions or the fnal state of an initially high-eccentricity
planet that migrated closer to its parent star
An earth sized_planet_with_an_earth_sized_densitySérgio Sacani
1) Researchers observed the exoplanet Kepler-78b using the HARPS-N spectrograph to measure its mass.
2) They measured Kepler-78b's mass to be 1.86 Earth masses, giving it a density similar to Earth, implying a rocky composition of iron and rock.
3) The small size of Kepler-78b makes it the smallest exoplanet yet measured for both mass and radius, establishing that Earth-sized planets can be terrestrial.
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
AT 2022aedm and a New Class of Luminous, Fast-cooling Transients in Elliptica...Sérgio Sacani
This document reports the discovery and follow-up observations of a remarkable fast-evolving optical transient called AT 2022aedm. Key points:
- AT 2022aedm was discovered by the ATLAS survey and reached an extremely luminous peak magnitude of Mg ≈ -22 mag.
- It exhibited an unusually fast rise time of 9 days and faded by 2 magnitudes in the following 15 days.
- Most surprisingly, its host galaxy was found to be a massive elliptical galaxy with negligible star formation.
- Extensive follow-up observations including spectroscopy found it shared properties with two other similar transients in passive galaxies, suggesting a new class of "luminous fast coolers." However
Spirals and clumps in V960 Mon: signs of planet formation via gravitational i...Sérgio Sacani
The formation of giant planets has traditionally been divided into two pathways: core accretion and gravitational instability. However, in recent years, gravitational instability has become less favored, primarily due
to the scarcity of observations of fragmented protoplanetary disks around young stars and low occurrence rate
of massive planets on very wide orbits. In this study, we present a SPHERE/IRDIS polarized light observation
of the young outbursting object V960 Mon. The image reveals a vast structure of intricately shaped scattered
light with several spiral arms. This finding motivated a re-analysis of archival ALMA 1.3 mm data acquired
just two years after the onset of the outburst of V960 Mon. In these data, we discover several clumps of continuum emission aligned along a spiral arm that coincides with the scattered light structure. We interpret the
localized emission as fragments formed from a spiral arm under gravitational collapse. Estimating the mass of
solids within these clumps to be of several Earth masses, we suggest this observation to be the first evidence of
gravitational instability occurring on planetary scales. This study discusses the significance of this finding for
planet formation and its potential connection with the outbursting state of V960 Mon.
Discovery and properties of the earliest galaxies with confirmed distancesSérgio Sacani
Surveys with James Webb Space Telescope (JWST) have discovered candidate galaxies in
the first 400 Myr of cosmic time1-5
. The properties of these distant galaxies provide initial
conditions for understanding early galaxy formation and cosmic reionisation6
. Preliminary
indications have suggested these candidate galaxies may be more massive and abundant
than previously thought1,7-9
. However, without spectroscopic confirmation of their
distances to constrain their intrinsic brightnesses, their inferred properties remain
uncertain. Here we report on four galaxies located in the JWST Advanced Deep
Extragalactic Survey (JADES) Near-Infrared Camera (NIRCam) imaging with
photometric redshifts � ∼ �� − �� subsequently confirmed by JADES JWST NearInfrared Spectrograph (NIRSpec) observations10. These galaxies include the first redshift
� > �� systems both discovered and spectroscopically confirmed by JWST. Using stellar
population modelling, we find the galaxies typically contain a hundred million solar masses
in stars, in stellar populations that are less than one hundred million years old. The
moderate star formation rates and compact sizes suggest elevated star formation rate
surface densities, a key indicator of their formation pathways. Taken together, these
measurements show that the first galaxies contributing to cosmic reionisation formed
rapidly and with intense internal radiation fields.
Similar to Large heterogeneities in_comet_67_p_as_revealed_by_active_pits_from_sinkhole_collapse (20)
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.
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.
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.
Detectability of Solar Panels as a TechnosignatureSérgio Sacani
In this work, we assess the potential detectability of solar panels made of silicon on an Earth-like
exoplanet as a potential technosignature. Silicon-based photovoltaic cells have high reflectance in the
UV-VIS and in the near-IR, within the wavelength range of a space-based flagship mission concept
like the Habitable Worlds Observatory (HWO). Assuming that only solar energy is used to provide
the 2022 human energy needs with a land cover of ∼ 2.4%, and projecting the future energy demand
assuming various growth-rate scenarios, we assess the detectability with an 8 m HWO-like telescope.
Assuming the most favorable viewing orientation, and focusing on the strong absorption edge in the
ultraviolet-to-visible (0.34 − 0.52 µm), we find that several 100s of hours of observation time is needed
to reach a SNR of 5 for an Earth-like planet around a Sun-like star at 10pc, even with a solar panel
coverage of ∼ 23% land coverage of a future Earth. We discuss the necessity of concepts like Kardeshev
Type I/II civilizations and Dyson spheres, which would aim to harness vast amounts of energy. Even
with much larger populations than today, the total energy use of human civilization would be orders of
magnitude below the threshold for causing direct thermal heating or reaching the scale of a Kardashev
Type I civilization. Any extraterrrestrial civilization that likewise achieves sustainable population
levels may also find a limit on its need to expand, which suggests that a galaxy-spanning civilization
as imagined in the Fermi paradox may not exist.
Jet reorientation in central galaxies of clusters and groups: insights from V...Sérgio Sacani
Recent observations of galaxy clusters and groups with misalignments between their central AGN jets
and X-ray cavities, or with multiple misaligned cavities, have raised concerns about the jet – bubble
connection in cooling cores, and the processes responsible for jet realignment. To investigate the
frequency and causes of such misalignments, we construct a sample of 16 cool core galaxy clusters and
groups. Using VLBA radio data we measure the parsec-scale position angle of the jets, and compare
it with the position angle of the X-ray cavities detected in Chandra data. Using the overall sample
and selected subsets, we consistently find that there is a 30% – 38% chance to find a misalignment
larger than ∆Ψ = 45◦ when observing a cluster/group with a detected jet and at least one cavity. We
determine that projection may account for an apparently large ∆Ψ only in a fraction of objects (∼35%),
and given that gas dynamical disturbances (as sloshing) are found in both aligned and misaligned
systems, we exclude environmental perturbation as the main driver of cavity – jet misalignment.
Moreover, we find that large misalignments (up to ∼ 90◦
) are favored over smaller ones (45◦ ≤ ∆Ψ ≤
70◦
), and that the change in jet direction can occur on timescales between one and a few tens of Myr.
We conclude that misalignments are more likely related to actual reorientation of the jet axis, and we
discuss several engine-based mechanisms that may cause these dramatic changes.
The solar dynamo begins near the surfaceSérgio Sacani
The magnetic dynamo cycle of the Sun features a distinct pattern: a propagating
region of sunspot emergence appears around 30° latitude and vanishes near the
equator every 11 years (ref. 1). Moreover, longitudinal flows called torsional oscillations
closely shadow sunspot migration, undoubtedly sharing a common cause2. Contrary
to theories suggesting deep origins of these phenomena, helioseismology pinpoints
low-latitude torsional oscillations to the outer 5–10% of the Sun, the near-surface
shear layer3,4. Within this zone, inwardly increasing differential rotation coupled with
a poloidal magnetic field strongly implicates the magneto-rotational instability5,6,
prominent in accretion-disk theory and observed in laboratory experiments7.
Together, these two facts prompt the general question: whether the solar dynamo is
possibly a near-surface instability. Here we report strong affirmative evidence in stark
contrast to traditional models8 focusing on the deeper tachocline. Simple analytic
estimates show that the near-surface magneto-rotational instability better explains
the spatiotemporal scales of the torsional oscillations and inferred subsurface
magnetic field amplitudes9. State-of-the-art numerical simulations corroborate these
estimates and reproduce hemispherical magnetic current helicity laws10. The dynamo
resulting from a well-understood near-surface phenomenon improves prospects
for accurate predictions of full magnetic cycles and space weather, affecting the
electromagnetic infrastructure of Earth.
Extensive Pollution of Uranus and Neptune’s Atmospheres by Upsweep of Icy Mat...Sérgio Sacani
In the Nice model of solar system formation, Uranus and Neptune undergo an orbital upheaval,
sweeping through a planetesimal disk. The region of the disk from which material is accreted by
the ice giants during this phase of their evolution has not previously been identified. We perform
direct N-body orbital simulations of the four giant planets to determine the amount and origin of solid
accretion during this orbital upheaval. We find that the ice giants undergo an extreme bombardment
event, with collision rates as much as ∼3 per hour assuming km-sized planetesimals, increasing the
total planet mass by up to ∼0.35%. In all cases, the initially outermost ice giant experiences the
largest total enhancement. We determine that for some plausible planetesimal properties, the resulting
atmospheric enrichment could potentially produce sufficient latent heat to alter the planetary cooling
timescale according to existing models. Our findings suggest that substantial accretion during this
phase of planetary evolution may have been sufficient to impact the atmospheric composition and
thermal evolution of the ice giants, motivating future work on the fate of deposited solid material.
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.
Emergent ribozyme behaviors in oxychlorine brines indicate a unique niche for...Sérgio Sacani
Mars is a particularly attractive candidate among known astronomical objects
to potentially host life. Results from space exploration missions have provided
insights into Martian geochemistry that indicate oxychlorine species, particularly perchlorate, are ubiquitous features of the Martian geochemical landscape. Perchlorate presents potential obstacles for known forms of life due to
its toxicity. However, it can also provide potential benefits, such as producing
brines by deliquescence, like those thought to exist on present-day Mars. Here
we show perchlorate brines support folding and catalysis of functional RNAs,
while inactivating representative protein enzymes. Additionally, we show
perchlorate and other oxychlorine species enable ribozyme functions,
including homeostasis-like regulatory behavior and ribozyme-catalyzed
chlorination of organic molecules. We suggest nucleic acids are uniquely wellsuited to hypersaline Martian environments. Furthermore, Martian near- or
subsurface oxychlorine brines, and brines found in potential lifeforms, could
provide a unique niche for biomolecular evolution.
Continuum emission from within the plunging region of black hole discsSérgio Sacani
The thermal continuum emission observed from accreting black holes across X-ray bands has the potential to be leveraged as a
powerful probe of the mass and spin of the central black hole. The vast majority of existing ‘continuum fitting’ models neglect
emission sourced at and within the innermost stable circular orbit (ISCO) of the black hole. Numerical simulations, however,
find non-zero emission sourced from these regions. In this work, we extend existing techniques by including the emission
sourced from within the plunging region, utilizing new analytical models that reproduce the properties of numerical accretion
simulations. We show that in general the neglected intra-ISCO emission produces a hot-and-small quasi-blackbody component,
but can also produce a weak power-law tail for more extreme parameter regions. A similar hot-and-small blackbody component
has been added in by hand in an ad hoc manner to previous analyses of X-ray binary spectra. We show that the X-ray spectrum
of MAXI J1820+070 in a soft-state outburst is extremely well described by a full Kerr black hole disc, while conventional
models that neglect intra-ISCO emission are unable to reproduce the data. We believe this represents the first robust detection of
intra-ISCO emission in the literature, and allows additional constraints to be placed on the MAXI J1820 + 070 black hole spin
which must be low a• < 0.5 to allow a detectable intra-ISCO region. Emission from within the ISCO is the dominant emission
component in the MAXI J1820 + 070 spectrum between 6 and 10 keV, highlighting the necessity of including this region. Our
continuum fitting model is made publicly available.
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.
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
Or: Beyond linear.
Abstract: Equivariant neural networks are neural networks that incorporate symmetries. The nonlinear activation functions in these networks result in interesting nonlinear equivariant maps between simple representations, and motivate the key player of this talk: piecewise linear representation theory.
Disclaimer: No one is perfect, so please mind that there might be mistakes and typos.
dtubbenhauer@gmail.com
Corrected slides: dtubbenhauer.com/talks.html
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.
hematic appreciation test is a psychological assessment tool used to measure an individual's appreciation and understanding of specific themes or topics. This test helps to evaluate an individual's ability to connect different ideas and concepts within a given theme, as well as their overall comprehension and interpretation skills. The results of the test can provide valuable insights into an individual's cognitive abilities, creativity, and critical thinking skills
ESR spectroscopy in liquid food and beverages.pptxPRIYANKA PATEL
With increasing population, people need to rely on packaged food stuffs. Packaging of food materials requires the preservation of food. There are various methods for the treatment of food to preserve them and irradiation treatment of food is one of them. It is the most common and the most harmless method for the food preservation as it does not alter the necessary micronutrients of food materials. Although irradiated food doesn’t cause any harm to the human health but still the quality assessment of food is required to provide consumers with necessary information about the food. ESR spectroscopy is the most sophisticated way to investigate the quality of the food and the free radicals induced during the processing of the food. ESR spin trapping technique is useful for the detection of highly unstable radicals in the food. The antioxidant capability of liquid food and beverages in mainly performed by spin trapping technique.
Current Ms word generated power point presentation covers major details about the micronuclei test. It's significance and assays to conduct it. It is used to detect the micronuclei formation inside the cells of nearly every multicellular organism. It's formation takes place during chromosomal sepration at metaphase.
GBSN - Biochemistry (Unit 6) Chemistry of Proteins
Large heterogeneities in_comet_67_p_as_revealed_by_active_pits_from_sinkhole_collapse
1. LETTER doi:10.1038/nature14564
Large heterogeneities in comet 67P as revealed by
active pits from sinkhole collapse
Jean-Baptiste Vincent1
, Dennis Bodewits2
, Se´bastien Besse3
, Holger Sierks1
, Cesare Barbieri4
, Philippe Lamy5
, Rafael Rodrigo6,7
,
Detlef Koschny3
, Hans Rickman8,9
, Horst Uwe Keller10
, Jessica Agarwal1
, Michael F. A’Hearn2,11
, Anne-The´re`se Auger5
,
M. Antonella Barucci12
, Jean-Loup Bertaux13
, Ivano Bertini14
, Claire Capanna5
, Gabriele Cremonese15
, Vania Da Deppo16
,
Bjo¨rn Davidsson6
, Stefano Debei17
, Mariolino De Cecco18
, Mohamed Ramy El-Maarry19
, Francesca Ferri14
, Sonia Fornasier12
,
Marco Fulle20
, Robert Gaskell21
, Lorenza Giacomini14
, Olivier Groussin5
, Aure´lie Guilbert-Lepoutre2
, P. Gutierrez-Marques1
,
Pedro J. Gutie´rrez22
, Carsten Gu¨ttler1
, Nick Hoekzema1
, Sebastian Ho¨fner1
, Stubbe F. Hviid23
, Wing-Huen Ip24
, Laurent Jorda5
,
Jo¨rg Knollenberg23
, Gabor Kovacs1
, Rainer Kramm1
, Ekkehard Ku¨hrt23
, Michael Ku¨ppers25
, Fiorangela La Forgia4
, Luisa M. Lara22
,
Monica Lazzarin4
, Vicky Lee24
, Ce´dric Leyrat12
, Zhong-Yi Lin24
, Jose` J. Lopez Moreno22
, Stephen Lowry26
, Sara Magrin27
,
Lucie Maquet25
, Simone Marchi28
, Francesco Marzari27
, Matteo Massironi29
, Harald Michalik30
, Richard Moissl25
,
Stefano Mottola23
, Giampiero Naletto14,16,31
, Nilda Oklay1
, Maurizio Pajola14
, Frank Preusker23
, Frank Scholten23
,
Nicolas Thomas19
, Imre Toth32
& Cecilia Tubiana1
Pits have been observed on many cometary nuclei mapped by
spacecraft1–4
. It has been argued that cometary pits are a signature
of endogenic activity, rather than impact craters such as those on
planetary and asteroid surfaces. Impact experiments5,6
and models7,8
cannot reproduce the shapes of most of the observed cometary pits,
and the predicted collision rates imply that few of the pits are related
to impacts8,9
. Alternative mechanisms like explosive activity10
have
been suggested, but the driving process remains unknown. Here we
report that pits on comet 67P/Churyumov–Gerasimenko are active,
and probably created by a sinkhole process, possibly accompanied
by outbursts. We argue that after formation, pits expand slowly
in diameter, owing to sublimation-driven retreat of the walls.
Therefore, pits characterize how eroded the surface is: a fresh come-
tary surface will have a ragged structure with many pits, while an
evolved surface will look smoother. The size and spatial distribution
of pits imply that large heterogeneities exist in the physical, struc-
tural or compositional properties of the first few hundred metres
below the current nucleus surface.
Understanding the differences in local activity of comet nuclei helps
us to constrain how their surfaces have evolved since their formation.
From July to December 2014, the OSIRIS (Optical, Spectroscopic, and
Infrared Remote Imaging System) cameras on board Rosetta11
continu-
ously monitored the activity of comet 67P/Churyumov–Gerasimenko
(referred to, hereafter, as comet 67P) from about a 30 km distance from
the surface of the nucleus and resolved the fine structure of dust jets12
.
By means of stereo reconstruction, we found that broad jets can be
separated into narrower features, which are linked unambiguously to
quasi-circular depressions and to walls of alcoves that are a few tens to a
few hundreds of metres in diameter. These pits are remarkably sym-
metric and similar in size, and show interesting morphological details
such as horizontal layers and terraces, vertical striations, and a smooth
floor seeminglycovered with dust. Some of these pits are as deep as a few
hundred metres and provide a glimpse well below the nucleus surface.
We detected a set of 18 quasi-circular pits on the northern hemisphere
of comet 67P (Extended Data Table 1, Fig. 1). We observed that pits
tend to cluster in small groups, and that several pits are active (Fig. 2).
We measured the depth-to-diameter ratio (d/D) of the pits and found
that active pits have a high d/D 5 0.736 0.08, while pits that are cur-
rently inactive are much shallower with mean d/D 5 0.266 0.08
(Extended Data Table 1, Fig. 3). The d/D ratio of these active pits is
much higher than that of circular depressions on other comets:
d/D5 0.1 on comet 9P/Tempel 1 (ref. 4), and d/D 5 0.2 on comet
81P/Wild 2 (refs 13 and 14).
The difference in pit morphology on the three comets may reflect
their different histories. For Jupiter family comets, the time since the
last encounter with Jupiter is a proxy for the thermal history of the
surface. Comet 9P is considered to be more processed by sublimation
than comet 81P (ref. 3). In that view, comet 67P is relatively unpro-
cessed by sublimation because its perihelion was brought from 2.7
astronomical units (AU) to 1.2 AU by a close encounter with Jupiter
in 1959 (seeMethodssubsection ‘Orbitintegration’). Comet 81P is also
considered a young comet, but its pitted terrains are exposed to the Sun
at perihelion and so have experienced much stronger erosion than the
pitted areas on comet 67P even though it has spent less time in the
1
Max-Planck-Institut fu¨r Sonnensystemforschung, Justus-von-Liebig-Weg 3, 37077 Go¨ttingen, Germany. 2
University of Maryland, Department of Astronomy, College Park, Maryland 20742-2421, USA.
3
Scientific Support Office, European Space Research and Technology Centre/ESA, Keplerlaan 1, Postbus 299, 2201 AZ Noordwijk ZH, The Netherlands. 4
University of Padova, Department of Physics
and Astronomy, Vicolo dell’Osservatorio 3, 35122 Padova, Italy. 5
Laboratoire d’Astrophysique de Marseille, UMR 7326, CNRS and Aix Marseille Universite´, 13388 Marseille Cedex 13, France. 6
Centro
de Astrobiologia, CSIC-INTA, 28850 Torrejon de Ardoz, Madrid, Spain. 7
International Space Science Institute, Hallerstraße 6, 3012 Bern, Switzerland. 8
Department of Physics and Astronomy, Uppsala
University, Box 516, 75120 Uppsala, Sweden. 9
PAS Space Research Center, Bartycka 18A, 00716 Warszawa, Poland. 10
Institut fu¨r Geophysik und extraterrestrische Physik (IGEP), Technische
Universita¨t Braunschweig, Mendelssohnstraße 3, 38106 Braunschweig, Germany. 11
Akademie der Wissenschaften zu Go¨ttingen and Max-Planck-Institut fu¨r Sonnensystemforschung, Justus-von-
Liebig-Weg 3, 37077 Go¨ttingen, Germany. 12
LESIA-Observatoire de Paris, CNRS, Universite´ Pierre et Marie Curie, Universite Paris Diderot, 5 place Jules Janssen, 92195 Meudon, France. 13
LATMOS,
CNRS/UVSQ/IPSL, 11 boulevard d’Alembert, 78280 Guyancourt, France. 14
Centro di Ateneo di Studi ed Attivita` Spaziali ‘‘Giuseppe Colombo’’ (CISAS), University of Padova, via Venezia 15, 35131
Padova, Italy. 15
INAF, Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy. 16
CNR-IFN UOS Padova LUXOR, via Trasea 7, 35131 Padova, Italy. 17
Department of Industrial
Engineering, University of Padova, via Venezia 1, 35131 Padova, Italy. 18
University of Trento, via Mesiano 77, 38100 Trento, Italy. 19
Physikalisches Institut der Universita¨t Bern, Sidlerstraße 5, 3012
Bern, Switzerland. 20
INAF Osservatorio Astronomico, via Tiepolo 11, 34014 Trieste, Italy. 21
Planetary Science Institute, Tucson, Arizona 85719, USA. 22
Instituto de Astrofisica de Andalucia (CSIC),
Glorieta de la Astronomı`a s/n, 18008 Granada, Spain. 23
Deutsches Zentrum fu¨r Luft- und Raumfahrt (DLR), Institut fu¨r Planetenforschung, Rutherfordstraße 2, 12489 Berlin, Germany. 24
National
Central University, Graduate Institute of Astronomy, 300 Chung-Da Rd, Chung-Li 32054, Taiwan. 25
Operations Department, European Space Astronomy Centre/ESA, PO Box 78, 28691 Villanueva de la
Canada, Madrid, Spain. 26
The University of Kent, School of Physical Sciences, Canterbury, Kent CT2 7NZ, UK. 27
University of Padova, Deptartment of Physics and Astronomy, via Marzolo 8, 35131
Padova, Italy. 28
Solar System Exploration Research Virtual Institute, Southwest Research Institute, 1050 Walnut Street, Suite 300, Boulder, Colorado 80302, USA. 29
Dipartimento di Geoscienze,
University of Padova, via Giovanni Gradenigo 6, 35131 Padova, Italy. 30
Institut fu¨r Datentechnik und Kommunikationsnetze der Technische Universita¨t Braunschweig, Hans-Sommer-Straße 66, 38106
Braunschweig, Germany. 31
University of Padova, Department of Information Engineering, via Gradenigo 6/B, 35131 Padova, Italy. 32
Konkoly Observatory of the Hungarian Academy of Sciences, PO
Box 67, 1525 Budapest, Hungary.
2 J U L Y 2 0 1 5 | V O L 5 2 3 | N A T U R E | 6 3
2. inner Solar System. Deep active pits on comets are seemingly found
preferentially on surfaces that have not been notably eroded.
The terrain morphology inside the pits on comet 67P is not uniform
and is classified as: very smooth texture; fractured terrain, terraces and
alcoves; or globular texture. The globular texture is detected only in the
deep pits and at a few additional locationsonthe nucleus,where deeper
near-surface layers can be observed. This morphology extends to a
depth of at least 200m below the current nucleus surface (see, for
example, pit Seth_01, Extended Data Fig. 2).
Jets arise from the edges of active pits, primarily from heavily
fractured and globular morphologies (Fig. 2). However, the d/D
ratio cannot be explained by current sublimation-driven retreat
of the walls. Excavating a pit like Seth_01 by sublimating ice on
the wall and floor would take more than 7,000 years (Methods).
The cylindrical shape of most pits also provides evidence against
formation by erosion, because this would result in elongated
shapes and a latitudinal dependence of the pit distribution on
the surface.
a
c
b
d
Figure 2 | Jet-like features in the Seth region. a–d, Views of the main active
pit in the Seth region, at different angles of solar illumination. The illuminated
area of the pit is the south wall (a), the north wall (b), the east wall (c) and the
southeast wall (d). Blue arrows point to detected jets; red arrows indicate areas
where no activity could be observed, either from the walls or from their
surroundings. The left images are the original data; the right images are linearly
stretched in brightness to display the lowest 5% of the intensity values.
Ash_01Ash_01 Ash_02Ash_02
Ash_03Ash_03
Ash_04Ash_04
Ash_05Ash_05
Ash_06Ash_06
Seth_06Seth_06
Seth_03Seth_03
Seth_02Seth_02
Seth_01Seth_01
Seth_04Seth_04
Seth_05Seth_05
Hathor_01Hathor_01
Ma’at_01Ma’at_01
Ma’at_02Ma’at_02
Ma’at_03Ma’at_03
Bastet_01Bastet_01
Ma’at_04Ma’at_04
Figure 1 | Location of the pits considered in this study. A non-exhaustive catalogue of depressions sharing similar morphologies to those unambiguously linked
to jets in the Seth and Ma’at regions.
6 4 | N A T U R E | V O L 5 2 3 | 2 J U L Y 2 0 1 5
RESEARCH LETTER
3. The 380 pits observed on comet 9P have been associated with
explosive activity9
. In the weeks before its encounter with this comet,
the spacecraftDeep Impactobserved at least 10 outbursts, the largestof
which ejected an estimated (6–30) 3 104
kg of material10,15,16
. The
observations suggest that these outbursts originated from a series of
pits located in a belt around the nucleus. At 4.11 AU from the Sun, on
30 April 2014, OSIRIS observed an outburst on comet 67P (ref. 17).
Depending on the assumed size distribution of the ejected dust, the
resulting plume contained 103
–105
kg of material, and was thus of
similar magnitude to the outbursts observed on comet 9P. Such out-
bursts are too small to create the observed pits by explosive excavation.
Assuming a constant density12
of 470 kg m23
, a typical large active pit
on comet 67P would have contained approximately 109
kg of material,
104
times more than the upper limit on the mass of the material
excavated by the observed outburst.
We propose that the pits are formed via sinkhole collapse, when the
ceiling of a subsurface cavity becomes too thin to support itself (Fig. 4
and Methods). Because the size of sinkholes depends on the material
strength of the top layers, sinkholes in a given terrain are all of similar
size. They are characterized by circular depressions aligned with the
local gravity vector18
.
On cometary nuclei, the removal of subsurface volatiles may gen-
erate a void. Failure of the cavity’s ceiling propagates upward. From the
observed pit diameters and depths, and by treating the cavity’s roof as
an unsupported beam failing under its own weight, we estimate that
the collapsing layer has an average tensile strength of 50 Pa (Extended
Data Fig. 8 and Methods). This value is similar to the lower-limit
estimate based on overhangs on the surface19
. The collapse exposes
fresh material in the walls of the pit, which sublimates to produce the
observed jets. Such collapse may very well be the driver of the 30 April
2014 outburst from comet 67P and the mini-outbursts from comet 9P.
The morphology and expansion of the dust plume of the 30 April 2014
outburst from comet 67P suggest that most of the activity arose from
an area within 30u of latitude of the north pole17
, compatible with the
location of the pits in the Seth region.
The collapse itself is a sudden event, but the cavity 100–200 m below
the surface could have been growing over a much longer timescale. We
explore three cavity formation scenarios: (1) primordial voids inher-
ited from formation; (2) direct sublimation of super volatiles (CO and
CO2) as an evolutionary process; and (3) deep subsurface sublimation
triggered by a secondary source of energy.
(1) The primordial scenario implies that voids existed in the nucleus
since its formation. This is possible if the comet formed by slow accre-
tion of cometesimals of tens to hundreds of metres in size. Low col-
lision speeds would prevent crushing the cavities20
. A weakening of the
surface due to direct sublimation would trigger roof collapse.
(2) Cavity formation can also be an evolutionary process. Because
comet nuclei have very low thermal conductivity21
, direct sublimation
of hexagonal water ice at the required depths would occur at an extre-
mely low rate and can therefore be ruled out. It is possible, however, to
sublimate more volatile ices like CO and CO2 at lower temperatures.
The fact that we do not see pits everywhere suggests that these super
volatiles may not be distributed evenly inside the nucleus; such hetero-
geneity has been observed on the surface of other comets (9P, ref. 22;
103P, ref. 23).
(3) A subsurface energy source may provide the heat necessary to
sublimate a large cavity. A candidate is the phase transition in water ice
from an amorphous to a crystalline structure. Crystallization has been
used to explain many cometary activity features, and has been sug-
gested as the underlying process for the distant outbursts of comet
1P/Halley and the chaotic behaviour of comet 29P/Schwassmann–
Wachmann24
, orthe outburst ofcomet 17P/Holmes25
.Differentmodels
have placed the crystallization front at depths ranging from a few
metres to hundreds of metres26,27
. We find that a subsurface cavity of
the size ofthe observedpitswould require thephase transition ofatleast
600 kg of amorphous ice, corresponding to a sphere of 2 m in diameter
atmost(see Methods). The detailed calculationof theamountneededis
beyond the scope of this Letter.
Ultimately, regardless of the process creating the initial subsurface
cavity, active pits indicate that large structural and/or compositional
heterogeneities exist within the first few hundred metres below the
current nucleus surface of comet 67P. Clusters of active pits and col-
lapsed structures are signatures of former cavities underneath, and
reflect the thermal history of the nucleus.
Diameter, D (m)
0 50 100 150 200 250 300
d/D
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
Figure 3 | Depth-to-diameter ratio as a function of pit diameter. Filled
symbols describe active pits; empty symbols describe currently inactive pits.
Filled circles are active pits in the Seth region; filled squares are active pits in the
Ma’at region. The lower value of d/D for pits in the latter might indicate a
different formation mechanism. Error bars represent the uncertainties inherent
to the shape reconstruction technique (stereo-photogrammetry) used to
produce the digital terrain model of the comet12
.
Cavity
Pit
Figure 4 | Pit formation mechanism by sinkhole collapse. A typical comet
surface with a layer of dust covering a mixture of dust and volatile material. A
subsurface heat source sublimates surrounding ices. This gas then escapes or
relocates, thus forming a cavity. When the ceiling becomes too thin to support
its own weight it collapses, creating a deep, circular pit with a smooth bottom.
Newlyexposed material in thepit’s walls canstart to sublimate. Blue arrowsand
white lines describe the escape of volatiles and fracturing of the surrounding
material; red arrow shows the collapse of the cavity ceiling.
2 J U L Y 2 0 1 5 | V O L 5 2 3 | N A T U R E | 6 5
LETTER RESEARCH
4. Online Content Methods, along with any additional Extended Data display items
andSource Data, are available in the onlineversion of the paper; references unique
to these sections appear only in the online paper.
Received 15 February; accepted 6 May 2015.
1. Keller, H. U., Kramm, R. & Thomas, N. Surface features on the nucleus of comet
Halley. Nature 331, 227–231 (1988).
2. Soderblom, L. A. et al. Observations of comet 19P/Borrelly by the miniature
integrated camera and spectrometer aboard Deep Space 1. Science 296,
1087–1091 (2002).
3. Brownlee, D. E. et al. Surface of young Jupiter family comet 81P/Wild 2: view from
the Stardust spacecraft. Science 304, 1764–1769 (2004).
4. Thomas, P. C. et al. The nucleus of comet 9P/Tempel 1: shape and geology from
two flybys. Icarus 222, 453–466 (2013).
5. A’Hearn, M. F. et al. Deep Impact: excavating comet Tempel 1. Science 310,
258–264 (2005).
6. Schultz, P., Hermalyn, B. & Veverka, J. The Deep Impact crater on 9P/Tempel-1
from Stardust-NExT. Icarus 222, 502–515 (2013).
7. Holsapple, K. A. & Housen, K. R. A crater and its ejecta: an interpretation of Deep
Impact. Icarus 187, 345–356 (2007).
8. Vincent, J.-B., Oklay, N., Marchi, S., Ho¨fner, S. & Sierks, H. Craters on comets. Planet.
Space Sci. 107, 53–63 (2015).
9. Belton, M.J.S. etal.Theoriginofpitson9P/Tempel 1 and the geologicsignature of
outbursts in Stardust-NExT images. Icarus 222, 477–486 (2013).
10. Belton, M. J. S. et al. Cometary cryo-volcanism: source regions and a model for the
UT 2005 June 14 and other mini-outbursts on comet 9P/Tempel 1. Icarus 198,
189–207 (2008).
11. Keller, H. U. et al. OSIRIS – The scientific camera system onboard Rosetta. Space
Sci. Rev. 128, 433–506 (2007).
12. Sierks, H. et al. On the nucleus structure and activity of comet 67P/Churyumov-
Gerasimenko. Science 347, aaa1044 (2015).
13. Kirk, R. et al. Topography of the 81/P Wild 2 nucleus derived from Stardust
stereoimages. Lunar Planet. Sci. XXXVI, 2244 (2005).
14. Basilevsky,A. T.& Keller,H.U. Comet nuclei: morphology and implied processes of
surface modification. Planet. Space Sci. 54, 808–829 (2006).
15. Farnham, T. L. et al. Dust coma morphology in the Deep Impact images of comet
9P/Tempel 1. Icarus 187, 26–40 (2007).
16. Feldman, P. D. et al. Hubble Space Telescope observations of comet 9P/Tempel 1
during the Deep Impact encounter. Icarus 187, 113–122 (2007).
17. Tubiana, C. et al. 67P/Churyumov-Gerasimenko:activity between Marchand June
2014 as observed from Rosetta/OSIRIS. Astron. Astrophys. 573, A62 (2015).
18. Waltham, T., Bell, F. G. & Culshaw, M. G. Sinkholes and Subsidence (Springer, 2007).
19. Thomas, N. et al. The morphological diversity of comet 67P/Churyumov-
Gerasimenko. Science 347, aaa0440 (2015).
20. Weissman, P. R., Asphaug, E. & Lowry, S. C. in Comets II (eds Festou, M. C. et al.)
337–357 (Univ. Arizona Press, 2004).
21. Groussin, O. et al. The temperature, thermal inertia, roughness and color of
the nuclei of comets 103P/Hartley 2 and 9P/Tempel 1. Icarus 222, 580–594
(2013).
22. Feaga, L. M., A’Hearn, M. F., Sunshine, J. M., Groussin, O. & Farnham, T. L.
Asymmetries in the distribution of H2O and CO2 in the inner coma of comet
9P/Tempel 1 as observed by Deep Impact. Icarus 190, 345–356 (2007).
23. A’Hearn, M. F. et al. EPOXI at comet Hartley 2. Science 332, 1396–1400 (2011).
24. Prialnik, D., Benkhoff, J. & Podolak, M. in Comets II (eds Festou, M. C. et al.) 359–387
(Univ. Arizona Press, 2004).
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behavior of comet 17P/Holmes. Icarus 221, 147–159 (2012).
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Acknowledgements OSIRIS was built by a consortium of the Max-Planck-Institut fu¨r
Sonnensystemforschung, Katlenburg-Lindau, Germany, the CISAS, University of
Padova, Italy, the Laboratoire d’Astrophysique de Marseille, France, the Instituto de
Astrofı´sica de Andalucia, CSIC, Granada, Spain, the Research and Scientific Support
Department of the European Space Agency, Noordwijk, The Netherlands, the Instituto
Nacional de Te´cnica Aeroespacial, Madrid, Spain, the Universidad Polite´chnica de
Madrid, Spain, the Department of Physics and Astronomy of Uppsala University,
Sweden,andthe Institut fu¨r Datentechnik und Kommunikationsnetze der Technischen
Universita¨t Braunschweig, Germany. The support of the national funding agencies of
Germany (DLR), France (CNES), Italy (ASI), Spain (MEC), Sweden (SNSB), and the ESA
Technical Directorate is acknowledged. This work was also supported by NASA JPL
contract 1267923 to the University of Maryland (M.F.A’H. and D.B.). M.F.A’H. is a Gauss
Professor at the Akademie der Wissenschaften zu Go¨ttingen and Max-Planck-Institut
fu¨r Sonnensystemforschung (Germany). This research has made use of NASA’s
Astrophysics Data System Bibliographic Services. We thank H. J. Melosh for reviews
and criticism.
Author Contributions J.-B.V.ledthestudy,identifiedthepitsandmeasuredtheir global
parameters. D.B. analysed outbursts and phase change transitions and prepared the
sinkhole model. S.B. performed the detailed morphology analysis. H.S., C.B., P.L., R.R.,
D.K. and H.R. are the lead scientists of the OSIRIS project. The other authors are
co-investigatorswho built andranthis instrumentand made the observationspossible,
and associates and assistants who participated in the study.
Author Information All data presented in this paper will be delivered to the ESA’s
Planetary Science Archive and NASA’s Planetary Data System in accordance with the
schedule established by the Rosetta project and will be available on request beforethat
archiving. Reprints and permissions information is available at www.nature.com/
reprints. The authors declare no competing financial interests. Readers are welcome to
comment on the online version of the paper. Correspondence and requests for
materials should be addressed to J.-B.V. (vincent@mps.mpg.de).
6 6 | N A T U R E | V O L 5 2 3 | 2 J U L Y 2 0 1 5
RESEARCH LETTER
5. METHODS
Detection of activity. Cometary activity is typically defined as the ensemble of
physical processes forming the gas and dust coma that escapes from the nucleus.
The main driver of activity is the solar insolation, which triggers the sublimation of
volatiles trapped in the subsurface of the nucleus28
. The liberated gas expands into
vacuum and drags along refractory grains from the surface. It has been known
since the first in situ mission to a comet that this activity is not uniformly dis-
tributed over the nucleus although the reasons for this anisotropy are not well
understood1
.
From the uneven distribution of active sources on the surface, anisotropies in
the coma arise in the form of narrow dusty streams (hereafter called ‘jets’), which
expand straight from the nucleus for at least some distance29
. Neither their source
nor the physics of their formation have been fully explained yet, although many
authors have proposed some explanations such as patches of enhanced H2O ice
content, localized super-volatile release from steep-sided pits, or repetitive mini-
outbursts30
. It is not clear whether these features are linked to volatiles at their
footprint or if they trace the shock front between competing gas flows from nearby
areas31
.
In OSIRIS images, jets appear as fuzzy streams of bright material arising from
specific areas on the nucleus surface. They are typically detected against the coma
or a dark background, which can be either empty space or cast shadows. They are
seen at all spatial scales, from large features spanning several tens of kilometres,
down to the limit of spatial resolution. The smallest features detected so far are a
few pixels across, which translates into a couple of metres at most. Their typical
surface brightness is 10% to 40% higher than the surrounding background space,
that is,the general coma12
. Bymonitoring the activity andobservingthese jets from
different angles we can perform stereo imaging, reconstruct their three-dimen-
sional structure and trace them back precisely to morphological features on the
surface.
Orbit integration. Observations and orbit reconstructions have shown that
comet 67P had a close encounter with Jupiter that brought its perihelion from
2.7 AU to 1.2 AU, in 1959 (JPL Horizons ephemerides, http://ssd.jpl.nasa.gov/hor-
izons.cgi). We reconstructed its orbit before that time, on the basis of a well-
established integration model32
. For the initial conditions and their errors, we refer
to the database of IMCCE (http://www.imcce.fr/langues/en/ephemerides/). We
compute 200 clone orbits with random Gaussian small variations of the initial
conditions considering their Gaussian errors. From these 200 clone orbits, we
deduce the mean perihelion distance and its standard deviation (s). We find that
84% of the orbits in the interval [(mean 2 s), (mean 1 s)] and the orbits beyond
(mean 1 s) have a perihelion distance greater than at least 2 AU with a mean value
always greater than 3 AU (Extended Data Fig. 1).
Morphology, variegation and activity of the pits. The pit morphologies are
presented in more detail in Extended Data Figs 3, 4. The complete list of
OSIRIS images used for this study is given in Extended Data Table 2.
The activity identified in Seth_01 covers the portion of the pit presented in
Fig. 1, which displays different morphologies and textures. Therefore, it is not clear
at this point that a specific texture and morphology is linked to the active pits. The
detailed observations of the pits Ma’at_01 and Ma’at_02 seem to indicate that
heavily fractured terrains are, however, favourably associated with activity.
Extended Data Fig. 3 highlights the multiple joints that are also associated with
the globular texture for Ma’at_01. Thus, fractured texture might be favourable for
these active pits, probably because it allows the heat to propagate deeper into the
interior and sublimate the ices. One other possible location for the activity inside
the pits could be the terraces seen in Seth_01 (and maybe in Ma’at_02, although
they are less developed). The two terraces highlighted in Extended Data Fig. 3
cover around 50% of the circumference of the Seth_01 pit, and they match the 50%
where activity has been identified so far. Therefore, the terraces could be the source
of the activity if they expose some kind of fresh ice (or gas/ice from the coma falling
back and depositing on this flat surface).
The contact between the edges of the pits and the surroundings is different
between the active pits Seth_01 and Ma’at_01. This could be the result of different
mechanisms that formed them or the primordial morphology of the region. The
bottoms of most pits are covered with a fine dusty material and boulders, which
could be an indication of the relative age of these pits. Seth_01’s floor appears very
flat (Extended Data Figs 3, 4), with a very smooth structure that does not contain
any boulders. The floors of Seth_02 and Seth_03, pits where activity has been
identified, share the same textural characteristics as Seth_01. The viewing condi-
tions are less favourable for Ma’at_01; however, Extended Data Figs 3–5 show few
boulders, all of small size. The same figures highlight that Ma’at_02 has a much
higher number of boulders with larger sizes. These boulders may be an indirect
way of estimating the relative age of the pits, because boulders accumulate with
time. Thus, boulder-free floors represent the youngest pits. The relative age dating
of these pits could also be speculated from the Ma’at_01 to Ma’at_03 series of pits.
With Ma’at_01 being the youngest and Ma’at_03 the oldest, one can see the
degradation of the wall of the pits and the accumulation of material within
the pit. The accumulation of boulders is rather limited in Ma’at_03, although
the degradation of the rim is in a more advanced stage when compared to the
other two, which confirms that it is the oldest. This low accumulation could be due
to the geometry of Ma’at_03 or related to the original depth of the pit, which is
most likely to have been smaller. The boulder-size distributions in the Seth and
Ma’at pits are shown in Extended Data Figs 5, 6.
We used additional images obtained through filters near the visible spectrum
(blue: 480 nm, orange: 649 nm, infrared: 989 nm) to see if, in addition to the
peculiar morphology, pits present a different colour to the rest of the surface. By
using filter ratios to limit the effect of topography and illumination conditions, we
found that the floor and walls of the pits exhibit the same less-red spectral slope as
the active Hapi region (Extended Data Fig. 7). If we denote the reflectance by R,
then we measure a ratio Rinfrared/Rblue 5 1.8 in the active area (pits) and Rinfrared/
Rblue 5 2.1 elsewhere on the nucleus. A full understanding of the implications of
the compositional differences within the nucleus will require a dedicated invest-
igation, but the difference in spectral slope observed in Extended Data Fig. 7
already indicates that spectral variation is an intrinsic property of currently active
regions on comet 67P.
Pit growth. A major question is whether the d/D ratio of the pits can be explained
by the current sublimation-driven retreat of the walls. We see jets arising from the
edges of active pits (Fig. 1), indicating that erosion currently does occur. We first
consider slowly excavating a pit by sublimating subsurface ice on the walls and
floor and growing the depressions in both diameter and depth. We take as an
example the most active pit (Seth_01). With a diameter of 220 m and a depth
of 185 m, it has a volume of 73 106
m3
, which corresponds to 3.33 109
kg of
material if we assume a constant density of 470kg m23
. Current models of activity
for comet 67P (refs 33–35) describe a global dust production rate of 9.3 kg s21
at 3.5 AU, which translates into only 15 g s21
of dust emitted from a single pit.
Additionally, the varying latitudes and seasons limit the pits’ illumination to only a
few hours per comet day for the walls. In some cases, the pit floor is only barely
illuminated, if at all. Considering that most currently observed pits will be in polar
night at perihelion and will not experience many changes in dust production rate,
it would take more than 7,000 years to dig out one pit.
Erosion is a second-order process that will slowly modify the pits after they are
formed. This is supported by our observations; several active pits display alcoves
within their walls, which we interpret as signatures of continued growth as a result
of erosion by sublimation, block falls and wall retreats long after the pit formation,
because these alcoves are always facing the direction of most insolation received
per comet rotation.
Phase transition. Crystallization has been invoked to explain many cometary activ-
ity features, and has been suggested as the underlying process for the distant out-
bursts of comet 1P/Halley24
, the chaotic behaviour of comet 29P/Schwassmann–
Wachmann24
and the violent outburst of comet 17P/Holmes25
.
From the ratio between the latent heat of the amorphous-to-crystalline transition
(93104
Jkg21
, refs 36, 37) and of the sublimation of hexagonal ice (0.334Jkg21
),
the phase transition of 1kg of amorphous ice to crystalline ice provides enough
energy to sublimate 270kg of hexagonal ice, provided that crystallization occurs
on a timescale short enough for the phase transition to effectively heat the surround-
ing ice. Using typical low thermal inertia, Marboeuf and Schmitt28
find that crystal-
lization proceeds to a depth of only approximately 1 m. Other studies estimate that
the crystallization front should extend to depths of between about 5 m and about 80
m (ref. 37), or much greater depths27
.
Given the chaotic orbital evolution of comet 67P, we estimate that a 100m deep
layer could have recently reached the appropriate characteristics (100–120K lead-
ing to a phase transition on a timescale of months to a year) only if the local
thermal inertia is high (250 J m22
K21
s21/2
and above), a value more than five
times what has been measured on comet 67P. For lower values of the thermal
inertia, the phase transition can occur at a depth of 100–200 m only after a long
period of time in the inner Solar System. A cavity could have formed much earlier
in the history of the comet, even if the final collapse that produced the observed
sinkhole occurred only recently. A subsurface cavity the size of the pits we observe
would require the phase transition of approximately 600kg of amorphous ice to
crystalline ice. If we assume a density of 470kg m23
and a porosity of 70–80%, we
obtain a 20–40% ice mass fraction in the nucleus (ice density is 920kg m23
,
solid material is half silicate and half organics, with respective densities of
3,500 kg m23
and 2,200kg m23
). Therefore, 600kg of ice would be embedded
in 1,500–3,000 kg of cometary material and would occupy a volume of 3–6m3
, that
is, a sphere of at most 2 m in diameter. Upon experiencing its phase transition, this
pocket of amorphous ice would release enough heat to sublimate the surrounding
crystalline ice in a volume equivalent to the observed pits.
LETTER RESEARCH
6. Sinkhole model. A first order estimate of the stability of a cavity ceiling may be
derived by treating the ceiling a beam failing under its own weight18,38
. Failure of
this beam occurs when the bending moment exceeds the material’s tensile
strength. Assuming the comet’s material is highly porous, the stable beam depth
d 5 6D2
ra/(8S), where D is the cavity’s diameter, r is the density of the material in
the ceiling (assumed to be 470 kg m23
), a is the gravitational acceleration on the
comet12
(53 1024
m s22
) and S is the tensile strength of the ceiling material. For
the tensile strength, we adopted an initial range between the lower limit of 10 Pa
derived from overhangs on the surface19
and the upper limit of 10 kPa derived
from the Deep Impact experiment39
. We further assume that the cavity is of
approximately the same size as the resulting pit and that the depth of the pit is
comparable to the depth of the original ceiling.
Code availability. The code used to generate the orbital evolution of comet 67P is
a direct implementation of a published model32
.
28. Delsemme,A.H.inComets(ed.Wilkening,L.L.)85–130(Univ.ArizonaPress,1982).
29. Sekanina, Z. Anisotropic emission from comets: fans versus jets. I. Concept and
modeling. In Proc. International Symposium on the Diversity and Similarity of Comets,
Vol. ESA SP-278, 315–322 (1987).
30. Belton, M. J. S. Cometary activity, active areas, and a mechanism for collimated
outflows on 1P, 9P, 19P, and 81P. Icarus 210, 881–897 (2010).
31. Crifo, J.-F., Rodionov, A. V., Szego¨, K. & Fulle, M. Challenging a paradigm: do we
need active and inactive areas to account for near-nuclear jet activity? Earth Moon
Planets 90, 227–238 (2002).
32. Marsden, B.G., Sekanina, Z.& Yeomans, D. K. Cometsandnon-gravitationalforces.
V. Astron. J. 78, 211–225 (1973).
33. Tozzi, G. P. et al. Evolution of the dust coma in comet 67P/Churyumov-
Gerasimenko before the 2009 perihelion. Astron. Astrophys. 531, A54 (2011).
34. Lara, L. M., Lin, Z.-Y., Rodrigo, R. & Ip, W.-H. 67P/Churyumov-Gerasimenko activity
evolution during its last perihelion before the Rosetta encounter. Astron. Astrophys.
525, A36 (2011).
35. Snodgrass, C. et al. Beginning of activity in 67P/Churyumov-Gerasimenko and
predictions for 2014–2015. Astron. Astrophys. 557, A33 (2013).
36. Ghormley, J. A. Enthalpy changes and heat-capacity changes in the
transformations from high-surface-area amorphous ice to stable hexagonal ice.
J. Chem. Phys. 48, 503–508 (1968).
37. De Sanctis, M. C., Lasue, J. & Capria, M. T. Seasonal effects on comet nuclei
evolution: activity, internal structure, and dust mantle formation. Astron. J. 140,
1–13 (2010).
38. White, W. B. Geomorphology and Hydrology of Karst Terrains (Oxford Univ. Press,
1988).
39. Richardson, J.E.& Melosh, H.J.AnexaminationoftheDeepImpactcollisionsiteon
comet Tempel 1 via Stardust-NExT: placing further constraints on cometary
surface properties. Icarus 222, 492–501 (2013).
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7. Extended Data Figure 1 | Perihelion distance of comet 67P as a function of
time. Solid line, mean value of the orbits integrated according to a Monte Carlo
method. Dashed lines, standard deviation of the mean value. a, Perihelion
distance over the last 270 years, when comet 67P experienced several close
encounters with Jupiter. b, The long term integration over the full dynamical
lifetime of the comet (10,000 years).
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8. Extended Data Figure 2 | Multiple views of the Seth_01 pit observed by the
OSIRIS camera. a, Southern part of the pit wall; b, western part of the pit wall;
c, d, eastern part of the pit wall with different illumination conditions; and
e, southeastern part of the pit wall observed in the shadow. In all the images, the
green arrow points to the same boulder and the blue arrow to the same ridge
inside the pit. The orange arrows point to terraces within the pit. The Seth_01
pit is 220 m in diameter.
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9. Extended Data Figure 3 | Multiple views of the Ma’at_01, Ma’at_02 and
Ma’at_03 pits observed by the OSIRIS camera. a, b, Side views of the pits with
different illumination conditions; c, opposite viewing conditions highlighting
the other side in the shadow; and d, e, detailed views of Ma’at_02 (d) and
Ma’at_01 (e) from light reflection in the shadow. Note the clear cross-cutting
fractures on the wall in e. In c, the white line is an artefact due to stretching of
the image to highlight the shadowed part. The Ma’at_02 pit is 130 m in
diameter. The blue, green and oranges arrows point to the same features in each
image.
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10. Extended Data Figure 4 | Additional views of the Seth_01 and Ma’at_01
pits. a, The floor of Seth_01 shows no accumulation of boulders; the same is
true for Seth_02 and Seth_03 (not shown). b, The floor of Ma’at_01 shows a few
boulders that have accumulated; note the activity located at the bottom. c, The
floor of Ma’at_02 shows an asymmetric accumulation of boulders that could
be the result of upper wall collapse.
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11. Extended Data Figure 5 | Boulder counts in Ma’at_01 and Ma’at_02. We
counted boulders on the floor of Ma’at_01 and Ma’at_02. We used OSIRIS
narrow angle camera (NAC) images with a resolution of 1.2 metres per pixel,
acquired at 67 km from the comet nucleus centre. a, b, The illumination
conditions are such that almost 80% of the floor of Ma’at_01 (a) and 95% of the
floor of Ma’at_02 (b) are illuminated and the pits are facing the observer,
which ensures an unbiased boulder count. We identified 23 boulders inside
Ma’at_01 and 68 on the floor of Ma’at_02. The diameter of the boulders
(in metres) is indicated by the coloured circles; see inset. Despite the 1.2 metres
per pixel resolution, we were able to identify some boulders with a diameter
between 1.5 m and 2.5 m (9 in Ma’at_01 and 15 in Ma’at_02), owing to the
presence of elongated shadows. The maximum boulder diameter is 4.3 m
in Ma’at_01 and 9.0 m in Ma’at_02.
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12. Extended Data Figure 6 | Cumulative boulder-size distribution for
Ma’at_01 and Ma’at_02. This distribution has a power index of {4:9z0:8
{0:7 for
Ma’at_01 (left) and {4:2z0:7
{0:6 for Ma’at_02 (right), for boulder diameters
greater than 3 m; the corresponding power laws are indicated the by the solid
(fit) lines. Boulders smaller than 3 m in diameter are at the edge of our detection
limit, meaning that the counts for these boulders are less reliable than the other
counts; consequently, they were not included when fitting the power law. The
higher number of boulders in Ma’at_02 is consistent with the theory that
bouldersaredebris that falls from thewalls asthepiterodes, long after the initial
formation of the pit. Error bars are defined as the square root of the cumulative
number of boulders to reflect the increasing diameter uncertainty for small
boulder sizes.
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13. Extended Data Figure 7 | RGB view of the Seth pits and the Hapi region.
The red–blue–green components of this colour map represent colour ratios
between the reflectance signals measured at different wavelengths: red, 989
nm/649 nm; green, 480 nm/649 nm; blue, 649 nm. The colour map is overlaid
onto a grey image showing the comet surface. The Hapi region and part of
Seth appear with a blue hue, indicative of a bluer spectral slope than other regions
of the nucleus, which are typically red. The interior of Seth_01, Seth_02 and
Seth_03 have the same blue hue that is characteristic of the active Hapi region.
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14. Extended Data Figure 8 | Modelled critical ceiling thickness for increasing
cavity diameter and different tensile strengths. We predict theaveragetensile
strength of a collapsed layer using the dimensions of a pit (Methods). For
example, a pit of 220 m in diameter and 185 m in depth (such as, Seth_01)
suggests that the collapsed layer had an average tensile strength of 50 Pa.
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15. Extended Data Table 1 | List of pits considered in this paper
Diameter and depth measured on digital terrain model reconstructed from OSIRIS images by stereo-photogrammetry12
. Active pits have a mean d/D 5 0.73 6 0.08; inactive pits have a mean d/D 5 0.26 6 0.08.
Maximum error is 20 m for the diameter and 5 m for the depth. Coordinates are given in the ‘Cheops’ reference frame12
.
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16. Extended Data Table 2 | List of images used
Also shown is the distance from the comet nucleus centre that the image was taken and the resolution of the image.
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