The document summarizes measurements and analysis of asteroid Bennu conducted during the OSIRIS-REx mission's preliminary survey phase. Key findings include:
1) Bennu's measured bulk density is 1,190 ± 13 kg m-3, consistent with a rubble-pile interior that is 40-50% empty space.
2) Global mapping of Bennu's surface slopes found a transition at the boundary of the "rotational Roche lobe", with more relaxed slopes inside the lobe likely due to particle redistribution.
3) Bennu's top-like shape and evidence of interior heterogeneity suggest it underwent spin-induced failure at some point, though when and how is still unknown.
Gravity and magnetic methods are an essential part of oil exploration. They do not replace seismic. Rather, they add to it. Despite being comparatively low-resolution, they have some very big advantages.
These geophysical methods passively measure natural variations in the earth’s gravity and magnetic fields over a map area and then try to relate these variations to geologic features in the subsurface. Lacking a controlled source, such surveys are usually environmentally unobjectionable.
The proposed VELOCITÉ mission aims to study geological activity and interior structure on Venus through a combination of orbital and lander-based instruments over a 5-year period. The orbital component, called VISAGE, would carry an interferometric synthetic aperture radar, ground penetrating radar, and high-precision gravity instruments to characterize surface topography, subsurface structure, and gravity field variations. Two landers, called LOVE 1 & 2, would conduct in-situ seismic and permittivity measurements to study near-surface structure. The mission aims to improve understanding of Venusian tectonics, volcanism, and interior dynamics.
- Gravity and magnetic mapping techniques measure small variations in the Earth's gravity and magnetic fields to infer properties of subsurface geology.
- Gravity mapping uses highly sensitive spring balances called gravimeters to detect variations as small as 0.001 mgal, while magnetic mapping uses electronic instruments to continuously record magnetic field variations.
- Corrections must be applied to gravity and magnetic data to account for factors like latitude, elevation, density variations, and temporal changes in the magnetic field.
- Interpretation of the residual anomaly maps provides constraints on the locations, shapes, and depths of subsurface density and magnetic sources, allowing inference of geological structures.
The document summarizes research on the origin of lunar concentric craters. The researchers analyzed data from Clementine, SELENE, and LRO to study 58 known concentric craters. They identified three morphological types and found concentric craters have shallower depths and smaller rim heights than fresh simple craters, suggesting impact degradation or uplift. Distribution near mare/highland boundaries and similarities to floor-fractured craters supports igneous intrusion as the most probable formation mechanism, rather than exogenic processes like simultaneous impacts or impact into layered targets.
Saturn’s magnetic field revealed by the Cassini Grand FinaleSérgio Sacani
Starting on 26 April 2017,
the Grand Finale phase of the Cassini mission
took the spacecraft through the gap between
Saturn’s atmosphere and the inner edge of its
innermost ring (the D-ring) 22 times, ending
with a final plunge into the atmosphere on
15 September 2017. This phase offered an opportunity
to investigate Saturn’s internal magnetic
field and the electromagnetic environment
between the planet and its rings. The internal
magnetic field is a diagnostic of interior structure,
dynamics, and evolution of
the host planet. Rotating convective
motion in the highly electrically
conducting layer of the planet
is thought to maintain the magnetic
field through the magnetohydrodynamic
(MHD) dynamo
process. Saturn’s internal magnetic
field is puzzling because of its
high symmetry relative to the spin
axis, known since the Pioneer 11
flyby. This symmetry prevents an
accurate determination of the rotation
rate of Saturn’s deep interior
and challenges our understanding
of the MHD dynamo process because
Cowling’s theorem precludes
a perfectly axisymmetric magnetic
field being maintained through an
active dynamo.
M6.0 2004 Parkfield Earthquake : Seismic AttenuationAli Osman Öncel
HRSN isimli kuyu içi sismik istasyonlar kullanılarak, San Andreas fayı boyunca meydana gelen büyük depremler öncesi sismik azalımın varlığının olup olmadığı araştırılıyor.
Similarities between gravity and magnetics and application of different geoph...Jyoti Khatiwada
The document discusses similarities and differences between gravity and magnetic geophysical survey methods. Some key similarities are that both measure naturally occurring fields of the Earth (gravity and magnetic), both use identical physical and mathematical representations, and data acquisition/reduction/interpretation are similar. Key differences include magnetic susceptibility varying more than density, magnetic forces can be attractive or repulsive while gravity is always attractive, and the magnetic field is time-dependent unlike gravity.
Gravity and magnetic methods are an essential part of oil exploration. They do not replace seismic. Rather, they add to it. Despite being comparatively low-resolution, they have some very big advantages.
These geophysical methods passively measure natural variations in the earth’s gravity and magnetic fields over a map area and then try to relate these variations to geologic features in the subsurface. Lacking a controlled source, such surveys are usually environmentally unobjectionable.
The proposed VELOCITÉ mission aims to study geological activity and interior structure on Venus through a combination of orbital and lander-based instruments over a 5-year period. The orbital component, called VISAGE, would carry an interferometric synthetic aperture radar, ground penetrating radar, and high-precision gravity instruments to characterize surface topography, subsurface structure, and gravity field variations. Two landers, called LOVE 1 & 2, would conduct in-situ seismic and permittivity measurements to study near-surface structure. The mission aims to improve understanding of Venusian tectonics, volcanism, and interior dynamics.
- Gravity and magnetic mapping techniques measure small variations in the Earth's gravity and magnetic fields to infer properties of subsurface geology.
- Gravity mapping uses highly sensitive spring balances called gravimeters to detect variations as small as 0.001 mgal, while magnetic mapping uses electronic instruments to continuously record magnetic field variations.
- Corrections must be applied to gravity and magnetic data to account for factors like latitude, elevation, density variations, and temporal changes in the magnetic field.
- Interpretation of the residual anomaly maps provides constraints on the locations, shapes, and depths of subsurface density and magnetic sources, allowing inference of geological structures.
The document summarizes research on the origin of lunar concentric craters. The researchers analyzed data from Clementine, SELENE, and LRO to study 58 known concentric craters. They identified three morphological types and found concentric craters have shallower depths and smaller rim heights than fresh simple craters, suggesting impact degradation or uplift. Distribution near mare/highland boundaries and similarities to floor-fractured craters supports igneous intrusion as the most probable formation mechanism, rather than exogenic processes like simultaneous impacts or impact into layered targets.
Saturn’s magnetic field revealed by the Cassini Grand FinaleSérgio Sacani
Starting on 26 April 2017,
the Grand Finale phase of the Cassini mission
took the spacecraft through the gap between
Saturn’s atmosphere and the inner edge of its
innermost ring (the D-ring) 22 times, ending
with a final plunge into the atmosphere on
15 September 2017. This phase offered an opportunity
to investigate Saturn’s internal magnetic
field and the electromagnetic environment
between the planet and its rings. The internal
magnetic field is a diagnostic of interior structure,
dynamics, and evolution of
the host planet. Rotating convective
motion in the highly electrically
conducting layer of the planet
is thought to maintain the magnetic
field through the magnetohydrodynamic
(MHD) dynamo
process. Saturn’s internal magnetic
field is puzzling because of its
high symmetry relative to the spin
axis, known since the Pioneer 11
flyby. This symmetry prevents an
accurate determination of the rotation
rate of Saturn’s deep interior
and challenges our understanding
of the MHD dynamo process because
Cowling’s theorem precludes
a perfectly axisymmetric magnetic
field being maintained through an
active dynamo.
M6.0 2004 Parkfield Earthquake : Seismic AttenuationAli Osman Öncel
HRSN isimli kuyu içi sismik istasyonlar kullanılarak, San Andreas fayı boyunca meydana gelen büyük depremler öncesi sismik azalımın varlığının olup olmadığı araştırılıyor.
Similarities between gravity and magnetics and application of different geoph...Jyoti Khatiwada
The document discusses similarities and differences between gravity and magnetic geophysical survey methods. Some key similarities are that both measure naturally occurring fields of the Earth (gravity and magnetic), both use identical physical and mathematical representations, and data acquisition/reduction/interpretation are similar. Key differences include magnetic susceptibility varying more than density, magnetic forces can be attractive or repulsive while gravity is always attractive, and the magnetic field is time-dependent unlike gravity.
Similarities and differences between gravity and magneticAkhtar Hussain
Geophysical exploration techniques that employ gravity and magnetic methods are passive, as they measure naturally occurring fields of the earth. Both gravity and magnetic fields are vector fields and force fields that exert force at the speed of light. While there are some similarities, there are also key differences between the two methods. The fundamental parameter controlling gravity variations is rock density, while the parameter for magnetic variations is magnetic susceptibility, which can vary widely even within the same rock type. Additionally, the gravitational field is always perpendicular to the earth's surface, whereas the magnetic field direction changes by location.
Geophysical surveys use physical methods at the Earth's surface to measure subsurface physical properties and anomalies. Types of geophysical surveys include gravity, magnetic, electrical, seismic, radiometric, and geothermal methods. The gravity method measures minute variations in gravity caused by differences in subsurface density and distance from the Earth's center. Gravity surveys can be aerial or land-based, using a highly sensitive gravimeter. Processed gravity data is plotted on maps showing variations indicating subsurface densities, and is used for hydrocarbon exploration, mineral deposits, cavity detection, and other applications.
Very regular high-frequency pulsation modes in young intermediate-mass starsSérgio Sacani
Asteroseismology probes the internal structures of stars by using their natural
pulsation frequencies1. It relies on identifying sequences of pulsation modes that can
be compared with theoretical models, which has been done successfully for many
classes of pulsators, including low-mass solar-type stars2, red giants3, high-mass stars4
and white dwarfs5. However, a large group of pulsating stars of intermediate mass—the
so-called δ Scuti stars—have rich pulsation spectra for which systematic mode
identification has not hitherto been possible6,7. This arises because only a seemingly
random subset of possible modes are excited and because rapid rotation tends to
spoil regular patterns8–10. Here we report the detection of remarkably regular
sequences of high-frequency pulsation modes in 60 intermediate-mass
main-sequence stars, which enables definitive mode identification. The space
motions of some of these stars indicate that they are members of known associations
of young stars, as confirmed by modelling of their pulsation spectra.
Geophysical prospecting uses physical methods to study the structure of the Earth's crust and locate minerals and ores. It involves collecting data using geophysical methods like seismic, gravitational, magnetic, electrical, and electromagnetic surveys. Seismic methods are commonly used in exploration. They involve generating seismic waves using sources like sledgehammers and analyzing the reflected and refracted waves detected by receivers to characterize subsurface layers and locate resources based on their elastic properties. Proper data acquisition, processing to reduce noise, and geological interpretation of processed seismic data are required to build an accurate model of the subsurface.
The document discusses gravity anomalies and density variations in different regions based on gravity data. It shows how gravity maps reveal details about crustal thickness, tectonic features like faults and volcanic zones, and plate boundaries. Specific examples discussed include the Tibetan Plateau, Central America subduction zone, an area in Chugoku, Japan, and the state of Florida in the US. Regional gravity data can be used to model density changes associated with plate tectonics, crustal evolution, and volcanic and tectonic activity.
1) Geophysical surveys have been using measurements of the Earth's magnetic field for nearly 500 years since Gilbert showed that the Earth behaves like a large magnet.
2) Gravity and magnetic surveying methods are similar in that they both measure naturally occurring fields (potential fields), can use identical physical representations like magnetic monopoles, and have similar data acquisition and interpretation.
3) However, magnetic surveying also has differences from gravity - magnetic susceptibility of rocks can vary more than density, magnetism can be attractive or repulsive unlike gravity, magnetic sources always occur in pairs unlike gravity, and the magnetic field is time-dependent unlike gravity.
The document discusses different geophysical methods used for subsurface exploration, including gravity, magnetic, electrical resistivity, and seismic methods. It focuses on explaining the gravity and magnetic methods. Gravity surveys measure differences in the gravitational field to detect variations in subsurface density distributions. Magnetic surveys map variations in the magnetic field caused by changes in magnetic susceptibility or structure of near-surface rocks. Both methods are used to locate features like hydrocarbon deposits, ore bodies, cavities, and buried structures or utilities.
Geophysical surveys use physical methods at the Earth's surface to measure subsurface physical properties and anomalies. Types of geophysical surveys include gravity, magnetic, electrical, seismic, radiometric, and geothermal methods. The gravity method measures minute variations in gravity caused by differences in subsurface density and distance from the Earth's center. Gravity surveys can be aerial or land-based, using a highly sensitive gravimeter. Processed gravity data is plotted on maps showing variations due to subsurface densities, and is used for hydrocarbon exploration, mineral deposits, cavity detection, and other applications.
Gravity anomaly across reagional structuresAmit K. Mishra
Gravity Anomaly across continents and ocean, gravity anomaly across mid-oceanic ridges, gravity anomaly across orogenic belts, and gravity anomaly across subduction zones.
Bouguer anomaly and free-air anomaly correlation signatures in parts of Benue...Premier Publishers
Topographic values in the study area range from 80m to 170m. The rock type comprises Basement Complex at the west bounded by River Niger, and sedimentary rock type in the east. Density measurements of various rocks were taken with the highest bulk density from the metamorphic schist (2.77gm/cm3), followed by igneous rock olivine gabbro (2.73gm/cm3), and sandstone (2.35gm/cm3). Results of gravity survey revealed a mean Bouguer anomaly of +12.15 mgals and a mean free air anomaly of +22.0 mgals. Interpretation of gravity measurements revealed the existence of a fracture at Gboloko NE-SW axis, a synclinal fold axis at about 5.5km west of Gboloko (between the Staurolite Schist and Cordierite-Tourmaline schist). The Basement-Sedimentary boundary is characterized by a drop in residual Bouguer anomaly from positive to negative at about 6km east of Gboloko. The thickness of the sediments is about 0.90km at the northern part of the Basement-Sedimentary boundary, and about 2.0km in the south, thus suggesting a progressive increase in sedimentary thickness at the western edge of the Benue trough. The Free-air anomaly ‘highs’ correspond to Bouguer anomaly ‘highs’ and tied to areas of high topography and bands of weathered, lateritized sediments. The Bouguer anomaly profiles exhibited reliable signature changes at the rock boundaries, thus a supportive tool for delineation of those border areas.
This document describes a model of crater formation on the Moon and terrestrial planets based on the current understanding of the impactor population in the inner Solar System. The model calculates impact rates spatially across planetary surfaces to account for nonuniform cratering. It finds that the lunar cratering rate varies with latitude and longitude, being about 25% lower in some regions and higher in others. The model reconciles measured lunar crater size-frequency distributions with observations of near-Earth objects, assuming the presence of a porous lunar megaregolith affects the size of small craters. It provides revised estimates of the ages of some lunar and planetary geological features based on crater counts and the derived crater chronology.
The gravity method involves measuring variations in the Earth's gravitational field to determine subsurface density variations. Gravity surveys measure differences in gravitational attraction at surface locations. After collecting data at regular intervals, corrections are applied for drift, elevation, tides and topography. The corrected anomalies are analyzed to infer subsurface geology, locating structures like faults, voids or buried valleys. Common applications include engineering, environmental and geothermal studies.
1) New data from the GRAIL gravity mission and LOLA altimetry is helping to determine the structure of the lunar highlands crust.
2) Preliminary GRAIL gravity models show noise levels are lower than expected, indicating signals exist at even shorter wavelengths than planned.
3) Combined analysis of gravity and topography data can provide insights into crustal thickness, elastic properties of the lithosphere, and the thermal state during and after bombardment.
1. The document discusses using seismicity data and geodetic strain measurements from GPS to develop integrated seismic hazard models for western Turkey and the eastern Mediterranean.
2. Statistical analysis of earthquake catalog data shows relationships between seismic clustering, b-values, and geodetic measurements of shear and dilatation strains across different scales.
3. The results provide insights into how seismicity varies with tectonic setting and stress conditions, which can help identify areas of increased seismic risk.
The presentation comprises the Gravity Method, It's anomaly, reduction, and its applications. The Gravity method is commonly used in Geology specifically in Geophysics.
Definition
Geophysics is the application of method of physics to the
study of the earth.
On the other sense, it is a subject of natural science
concerned with the physical processes and the physical
properties of the earth and its surrounding space
environment and the use of co-ordinate methods for the
analysis.
It involves the application of physical theories and
measurements to discover the properties and processes of the
earth.
A Gravity survey is an indirect (surface) means of calculating the density pr...Shahid Hussain
A Gravity survey is an indirect (surface) means of calculating the density property of subsurface materials. The higher the gravity values, the denser the rock beneath.
Geophysics is the study of the Earth, including its composition and structure, tectonic plates, earthquakes, and natural hazards. A geophysicist conducts seismic surveys using energy sources and geophones to collect and interpret data on subsurface structures. They use computer technology to process and visualize seismic data to find oil, gas, water, and other resources. Geophysics students gain experience through field trips and field schools. Geophysicists and technologists are employed by the petroleum industry, engineering companies, mining companies, universities, and governments.
This document proposes a new method for rapidly assessing the age of geological units on Mars using measurements of topographic roughness. It hypothesizes that roughness will be correlated with age derived from crater size-frequency distributions, as craters increase surface roughness over time. To test this, the author analyzes topography images and measures roughness from 125 sites across Mars. Age is calculated from crater counts and compared to roughness measurements. Preliminary results show a significant relationship between some roughness measures and age, though there is also variation likely due to crater degradation processes altering roughness without affecting size distributions. If validated, roughness could provide a faster way to assess relative Martian surface ages than traditional crater counting.
The unexpected surface of asteroid (101955) BennuSérgio Sacani
Bennu's surface was found to be more diverse and rugged than expected based on pre-encounter data. While its global properties like composition, shape and density matched predictions, high-resolution images revealed an unexpectedly wide range of albedos across its surface as well as many more large boulders than anticipated. This poses challenges for selecting a safe sample site. Magnetite detected on darker regions may indicate fresher material from aqueous alteration. More data is needed to understand Bennu's surface evolution and guide sample acquisition.
predicting the long term solar wind ion-sputtering source at mercuryJay Kim
This document summarizes research predicting the long-term solar wind ion-sputtering source at Mercury using data from the Helios spacecraft. The key points are:
1) Maps of solar wind proton flux onto Mercury's surface were constructed using a magnetosphere model and solar wind conditions estimated from Helios data when it was in Mercury's orbit.
2) Analysis of Helios data in Mercury's orbital range found that solar wind density increases by a factor of 2.3 from aphelion to perihelion, while velocity is independent of distance. IMF Bz is more likely to be strongly southward at perihelion.
3) Model runs used solar wind parameters matching the most probable conditions identified
Similarities and differences between gravity and magneticAkhtar Hussain
Geophysical exploration techniques that employ gravity and magnetic methods are passive, as they measure naturally occurring fields of the earth. Both gravity and magnetic fields are vector fields and force fields that exert force at the speed of light. While there are some similarities, there are also key differences between the two methods. The fundamental parameter controlling gravity variations is rock density, while the parameter for magnetic variations is magnetic susceptibility, which can vary widely even within the same rock type. Additionally, the gravitational field is always perpendicular to the earth's surface, whereas the magnetic field direction changes by location.
Geophysical surveys use physical methods at the Earth's surface to measure subsurface physical properties and anomalies. Types of geophysical surveys include gravity, magnetic, electrical, seismic, radiometric, and geothermal methods. The gravity method measures minute variations in gravity caused by differences in subsurface density and distance from the Earth's center. Gravity surveys can be aerial or land-based, using a highly sensitive gravimeter. Processed gravity data is plotted on maps showing variations indicating subsurface densities, and is used for hydrocarbon exploration, mineral deposits, cavity detection, and other applications.
Very regular high-frequency pulsation modes in young intermediate-mass starsSérgio Sacani
Asteroseismology probes the internal structures of stars by using their natural
pulsation frequencies1. It relies on identifying sequences of pulsation modes that can
be compared with theoretical models, which has been done successfully for many
classes of pulsators, including low-mass solar-type stars2, red giants3, high-mass stars4
and white dwarfs5. However, a large group of pulsating stars of intermediate mass—the
so-called δ Scuti stars—have rich pulsation spectra for which systematic mode
identification has not hitherto been possible6,7. This arises because only a seemingly
random subset of possible modes are excited and because rapid rotation tends to
spoil regular patterns8–10. Here we report the detection of remarkably regular
sequences of high-frequency pulsation modes in 60 intermediate-mass
main-sequence stars, which enables definitive mode identification. The space
motions of some of these stars indicate that they are members of known associations
of young stars, as confirmed by modelling of their pulsation spectra.
Geophysical prospecting uses physical methods to study the structure of the Earth's crust and locate minerals and ores. It involves collecting data using geophysical methods like seismic, gravitational, magnetic, electrical, and electromagnetic surveys. Seismic methods are commonly used in exploration. They involve generating seismic waves using sources like sledgehammers and analyzing the reflected and refracted waves detected by receivers to characterize subsurface layers and locate resources based on their elastic properties. Proper data acquisition, processing to reduce noise, and geological interpretation of processed seismic data are required to build an accurate model of the subsurface.
The document discusses gravity anomalies and density variations in different regions based on gravity data. It shows how gravity maps reveal details about crustal thickness, tectonic features like faults and volcanic zones, and plate boundaries. Specific examples discussed include the Tibetan Plateau, Central America subduction zone, an area in Chugoku, Japan, and the state of Florida in the US. Regional gravity data can be used to model density changes associated with plate tectonics, crustal evolution, and volcanic and tectonic activity.
1) Geophysical surveys have been using measurements of the Earth's magnetic field for nearly 500 years since Gilbert showed that the Earth behaves like a large magnet.
2) Gravity and magnetic surveying methods are similar in that they both measure naturally occurring fields (potential fields), can use identical physical representations like magnetic monopoles, and have similar data acquisition and interpretation.
3) However, magnetic surveying also has differences from gravity - magnetic susceptibility of rocks can vary more than density, magnetism can be attractive or repulsive unlike gravity, magnetic sources always occur in pairs unlike gravity, and the magnetic field is time-dependent unlike gravity.
The document discusses different geophysical methods used for subsurface exploration, including gravity, magnetic, electrical resistivity, and seismic methods. It focuses on explaining the gravity and magnetic methods. Gravity surveys measure differences in the gravitational field to detect variations in subsurface density distributions. Magnetic surveys map variations in the magnetic field caused by changes in magnetic susceptibility or structure of near-surface rocks. Both methods are used to locate features like hydrocarbon deposits, ore bodies, cavities, and buried structures or utilities.
Geophysical surveys use physical methods at the Earth's surface to measure subsurface physical properties and anomalies. Types of geophysical surveys include gravity, magnetic, electrical, seismic, radiometric, and geothermal methods. The gravity method measures minute variations in gravity caused by differences in subsurface density and distance from the Earth's center. Gravity surveys can be aerial or land-based, using a highly sensitive gravimeter. Processed gravity data is plotted on maps showing variations due to subsurface densities, and is used for hydrocarbon exploration, mineral deposits, cavity detection, and other applications.
Gravity anomaly across reagional structuresAmit K. Mishra
Gravity Anomaly across continents and ocean, gravity anomaly across mid-oceanic ridges, gravity anomaly across orogenic belts, and gravity anomaly across subduction zones.
Bouguer anomaly and free-air anomaly correlation signatures in parts of Benue...Premier Publishers
Topographic values in the study area range from 80m to 170m. The rock type comprises Basement Complex at the west bounded by River Niger, and sedimentary rock type in the east. Density measurements of various rocks were taken with the highest bulk density from the metamorphic schist (2.77gm/cm3), followed by igneous rock olivine gabbro (2.73gm/cm3), and sandstone (2.35gm/cm3). Results of gravity survey revealed a mean Bouguer anomaly of +12.15 mgals and a mean free air anomaly of +22.0 mgals. Interpretation of gravity measurements revealed the existence of a fracture at Gboloko NE-SW axis, a synclinal fold axis at about 5.5km west of Gboloko (between the Staurolite Schist and Cordierite-Tourmaline schist). The Basement-Sedimentary boundary is characterized by a drop in residual Bouguer anomaly from positive to negative at about 6km east of Gboloko. The thickness of the sediments is about 0.90km at the northern part of the Basement-Sedimentary boundary, and about 2.0km in the south, thus suggesting a progressive increase in sedimentary thickness at the western edge of the Benue trough. The Free-air anomaly ‘highs’ correspond to Bouguer anomaly ‘highs’ and tied to areas of high topography and bands of weathered, lateritized sediments. The Bouguer anomaly profiles exhibited reliable signature changes at the rock boundaries, thus a supportive tool for delineation of those border areas.
This document describes a model of crater formation on the Moon and terrestrial planets based on the current understanding of the impactor population in the inner Solar System. The model calculates impact rates spatially across planetary surfaces to account for nonuniform cratering. It finds that the lunar cratering rate varies with latitude and longitude, being about 25% lower in some regions and higher in others. The model reconciles measured lunar crater size-frequency distributions with observations of near-Earth objects, assuming the presence of a porous lunar megaregolith affects the size of small craters. It provides revised estimates of the ages of some lunar and planetary geological features based on crater counts and the derived crater chronology.
The gravity method involves measuring variations in the Earth's gravitational field to determine subsurface density variations. Gravity surveys measure differences in gravitational attraction at surface locations. After collecting data at regular intervals, corrections are applied for drift, elevation, tides and topography. The corrected anomalies are analyzed to infer subsurface geology, locating structures like faults, voids or buried valleys. Common applications include engineering, environmental and geothermal studies.
1) New data from the GRAIL gravity mission and LOLA altimetry is helping to determine the structure of the lunar highlands crust.
2) Preliminary GRAIL gravity models show noise levels are lower than expected, indicating signals exist at even shorter wavelengths than planned.
3) Combined analysis of gravity and topography data can provide insights into crustal thickness, elastic properties of the lithosphere, and the thermal state during and after bombardment.
1. The document discusses using seismicity data and geodetic strain measurements from GPS to develop integrated seismic hazard models for western Turkey and the eastern Mediterranean.
2. Statistical analysis of earthquake catalog data shows relationships between seismic clustering, b-values, and geodetic measurements of shear and dilatation strains across different scales.
3. The results provide insights into how seismicity varies with tectonic setting and stress conditions, which can help identify areas of increased seismic risk.
The presentation comprises the Gravity Method, It's anomaly, reduction, and its applications. The Gravity method is commonly used in Geology specifically in Geophysics.
Definition
Geophysics is the application of method of physics to the
study of the earth.
On the other sense, it is a subject of natural science
concerned with the physical processes and the physical
properties of the earth and its surrounding space
environment and the use of co-ordinate methods for the
analysis.
It involves the application of physical theories and
measurements to discover the properties and processes of the
earth.
A Gravity survey is an indirect (surface) means of calculating the density pr...Shahid Hussain
A Gravity survey is an indirect (surface) means of calculating the density property of subsurface materials. The higher the gravity values, the denser the rock beneath.
Geophysics is the study of the Earth, including its composition and structure, tectonic plates, earthquakes, and natural hazards. A geophysicist conducts seismic surveys using energy sources and geophones to collect and interpret data on subsurface structures. They use computer technology to process and visualize seismic data to find oil, gas, water, and other resources. Geophysics students gain experience through field trips and field schools. Geophysicists and technologists are employed by the petroleum industry, engineering companies, mining companies, universities, and governments.
This document proposes a new method for rapidly assessing the age of geological units on Mars using measurements of topographic roughness. It hypothesizes that roughness will be correlated with age derived from crater size-frequency distributions, as craters increase surface roughness over time. To test this, the author analyzes topography images and measures roughness from 125 sites across Mars. Age is calculated from crater counts and compared to roughness measurements. Preliminary results show a significant relationship between some roughness measures and age, though there is also variation likely due to crater degradation processes altering roughness without affecting size distributions. If validated, roughness could provide a faster way to assess relative Martian surface ages than traditional crater counting.
The unexpected surface of asteroid (101955) BennuSérgio Sacani
Bennu's surface was found to be more diverse and rugged than expected based on pre-encounter data. While its global properties like composition, shape and density matched predictions, high-resolution images revealed an unexpectedly wide range of albedos across its surface as well as many more large boulders than anticipated. This poses challenges for selecting a safe sample site. Magnetite detected on darker regions may indicate fresher material from aqueous alteration. More data is needed to understand Bennu's surface evolution and guide sample acquisition.
predicting the long term solar wind ion-sputtering source at mercuryJay Kim
This document summarizes research predicting the long-term solar wind ion-sputtering source at Mercury using data from the Helios spacecraft. The key points are:
1) Maps of solar wind proton flux onto Mercury's surface were constructed using a magnetosphere model and solar wind conditions estimated from Helios data when it was in Mercury's orbit.
2) Analysis of Helios data in Mercury's orbital range found that solar wind density increases by a factor of 2.3 from aphelion to perihelion, while velocity is independent of distance. IMF Bz is more likely to be strongly southward at perihelion.
3) Model runs used solar wind parameters matching the most probable conditions identified
The large-scale nebular pattern of a superwind binary in an eccentric orbitSérgio Sacani
Preplanetary nebulae and planetary nebulae are evolved,
mass-losing stellar objects that show a wide variety of morphologies.
Many of these nebulae consist of outer structures
that are nearly spherical (spiral/shell/arc/halo) and inner
structures that are highly asymmetric (bipolar/multipolar)1,2.
The coexistence of such geometrically distinct structures is
enigmatic because it hints at the simultaneous presence of
both wide and close binary interactions, a phenomenon that
has been attributed to stellar binary systems with eccentric
orbits3. Here, we report high-resolution molecular line observations
of the circumstellar spiral-shell pattern of AFGL 3068,
an asymptotic giant branch star transitioning to the preplanetary
nebula phase. The observations clearly reveal that the
dynamics of the mass loss is influenced by the presence of an
eccentric-orbit binary. This quintessential object opens a window
on the nature of deeply embedded binary stars through
the circumstellar spiral-shell patterns that reside at distances
of several thousand au from the stars.
Kinetic Energy Transfer of Near-Earth Objects for Interplanetary Manned Missi...Winston Sanks
This report outlines the rationale, procedures, technical feasibility, risk assessment, and cost-benefit analysis of utilizing a Near-Earth Object, 101955 Bennu (provisional designation 1999 RQ36 - the target of the OSIRIS-REx mission), as a source of energy to minimize the propulsion requirements of an interplanetary spacecraft. The planet Mars is the target body in this study and the outbound Trans-Mars injection in the years between 2175 and 2199 will be analyzed (within this timeframe Bennu’s orbit is predicted to approach Earth within two Earth radii on at least 80 occasions). The Mars orbit insertion burn, Trans-Earth injection burn, and Earth orbit insertion burn are assumed to be achieved with propulsive maneuvers outlined in standard manned interplanetary mission architectures. To accomplish this mission, two methods of transferring kinetic energy are examined: direct capture and release of the asteroid by a spacecraft using a Kevlar net and an inertial reel, and indirect capture by establishing a station on the asteroid to manufacture compressed material from the carbonaceous regolith in order to fire a mass stream to be captured by the spacecraft. This mission architecture analysis takes into account the associated safety risks of perturbations within Bennu’s orbit (which could result in inaccurate rendezvous location predictions), the implications of altering the orbit of 101955 Bennu after transferring a portion of its energy (since there is a possibility of collision with Earth in the late 22nd century if the asteroid is slowed too significantly), g-limit restrictions of the spacecraft and its occupants during an acceleration by the asteroid, and the possibility of a collision between Bennu and the spacecraft. In addition, the cost-benefit considerations of this mission architecture are weighed. This examination concludes that a direct capture Net and Reel system aboard the spacecraft is not a viable capture method due to an insufficient maximum ΔV available through a best-case perfectly elastic collision (capture) with the asteroid, as well as a prohibitive weight penalty aboard the spacecraft due to the Net and Reel system. However, this report finds that the method of establishing a station on Bennu with the capability to separate mass from the asteroid and fire it at a spacecraft is a plausible (if costly) means of transferring a significant ΔV. A KETNEO-FIMM Asteroid Station mission architecture could also be used in subsequent interplanetary missions providing cost-sharing over many decades for future interplanetary missions.
Craters, boulders and regolith of (101955) Bennu indicative of an old and dyn...Sérgio Sacani
- NASA's OSIRIS-REx mission arrived at the near-Earth asteroid Bennu in December 2018 and obtained images revealing its shape and surface features.
- Bennu has a diameter of 492 meters and is classified as a rubble pile asteroid, consisting of loosely bound fragments with high porosity.
- Images show numerous large boulders on Bennu's surface, some over 50 meters in size, indicating impacts in its past. Fractured boulders and impact breccias further suggest a dynamic history.
- The surface shows signs of both ancient features from the main asteroid belt as well as more recent mass movement, with clusters of boulders in low areas and incomplete crater
Lunar ejecta origin of near-Earth asteroid Kamo’oalewa is compatible with rar...Sérgio Sacani
Near-Earth asteroid, Kamo’oalewa (469219), is one of a small number of known quasisatellites of Earth; it transitions between quasi-satellite and horseshoe orbital states on
centennial timescales, maintaining this dynamics over megayears. The similarity of its
reflectance spectrum to lunar silicates and its Earth-like orbit both suggest that it originated
from the lunar surface. Here we carry out numerical simulations of the dynamical evolution of
particles launched from different locations on the lunar surface with a range of ejection
velocities in order to assess the hypothesis that Kamo‘oalewa originated as a debris-fragment
from a meteoroidal impact with the lunar surface. As these ejecta escape the Earth-Moon
environment, they face a dynamical barrier for entry into Earth’s co-orbital space. However, a
small fraction of launch conditions yields outcomes that are compatible with Kamo‘oalewa’s
orbit. The most favored conditions are launch velocities slightly above the escape velocity
from the trailing lunar hemisphere.
On the possibility of through passage of asteroid bodies across the Earth’s a...Sérgio Sacani
We have studied the conditions of through passage of asteroids with diameters 200, 100, and
50 m, consisting of three types of materials – iron, stone, and water ice, across the Earth’s
atmosphere with a minimum trajectory altitude in the range 10–15 km. The conditions of this
passage with a subsequent exit into outer space with the preservation of a substantial fraction
of the initial mass have been found. The results obtained support our idea explaining one of the
long-standing problems of astronomy – the Tunguska phenomenon, which has not received
reasonable and comprehensive interpretations to date. We argue that the Tunguska event was
caused by an iron asteroid body, which passed through the Earth’s atmosphere and continued
to the near-solar orbit.
Shape of (101955) Bennu indicative of a rubble pile with internal stiffnessSérgio Sacani
The document describes new findings about the asteroid Bennu based on images from the OSIRIS-REx spacecraft. It finds that Bennu has a top-like shape with considerable macroporosity and prominent boulders, suggesting it is a rubble pile. However, it also has high-standing ridges and surface features indicating some level of internal stiffness. The shape and features suggest Bennu formed by reaccumulation and past fast spin, but now its interior allows surface cracking and mass wasting. Key parameters of Bennu such as size, volume, density are consistent with prior estimates from Earth-based radar.
1) The gravitational slingshot effect allows spacecraft to gain kinetic energy from planetary flybys through a process explained by Newtonian physics and relativistic kinematics.
2) Relativistic analysis shows that a spacecraft's kinetic energy increases if it approaches a planet with a smaller exit angle compared to its entrance angle, and decreases if the exit angle is larger.
3) NASA has used the slingshot effect to boost spacecraft to explore the outer solar system, with Voyager gaining assistance from Jupiter and Cassini planned to receive boosts on its journey to Saturn.
The document describes the gravitational assist technique used by the Pioneer 10 spacecraft during its 1973 encounter with Jupiter. It begins by introducing the paradox that gravitational assist seems to contradict the expectation that a spacecraft's kinetic energy would remain the same after passing through a planet's gravitational field. It then provides details of Pioneer 10's encounter with Jupiter, showing how the spacecraft gained speed and switched to an escape trajectory from the solar system. Finally, it explains the physics behind gravitational assist, noting that the planet Jupiter experienced an equal and opposite change in velocity and kinetic energy compared to the spacecraft, resolving the paradox.
The document describes the gravitational assist technique used by the Pioneer 10 spacecraft during its 1973 encounter with Jupiter. It begins by introducing the paradox that gravitational assist seems to contradict the expectation that a spacecraft's kinetic energy would remain the same after passing through a planet's gravitational field. It then provides details of Pioneer 10's encounter with Jupiter, showing how the spacecraft gained speed and switched to an escape trajectory from the solar system. Finally, it explains the physics behind gravitational assist, noting that the planet Jupiter experienced an equal and opposite change in velocity and kinetic energy compared to the spacecraft, resolving the paradox.
The document summarizes the first observations of the magnetic Kelvin-Helmholtz instability in the solar corona using high-resolution imaging from NASA's Solar Dynamics Observatory. The instability was detected on the northern flank of a fast coronal mass ejection, appearing as substructures or waves against the darker coronal background. Analysis found the observed phase speed of the waves to be about half the speed of the ejecta front, validating theories of the non-linear dynamics of this instability in magnetized plasma environments. The findings provide new insights into fundamental plasma processes in the solar atmosphere and solar-terrestrial system.
Evidence for a_distant_giant_planet_in_the_solar_systemSérgio Sacani
A descoberta de um novo planeta, atualmente não é uma manchete que chama tanto assim a atenção das pessoas. Muito disso, graças ao Telescópio Espacial Kepler, que já descobriu quase 2000 exoplanetas e todo instante uma nova descoberta é anunciada, certo? Mais ou menos, a descoberta anunciada hoje, dia 20 de Janeiro de 2016, é um pouco diferente, pois não se trata de um exoplaneta, e sim de um novo planeta no Sistema Solar, e esse é um fato que intriga os astrônomos a muitos e muitos anos.
Porém, temos que ir com calma com esses anúncios. No artigo aceito para publicação no The Astronomical Journal (artigo no final do post), os autores, Mike Brown e Konstantin Batygin, do Instituto de Tecnologia da Califórnia, apresentaram o que eles dizem ser evidências circunstâncias fortes para a existência de um grande planeta ainda não descoberto, talvez, com uma massa 10 vezes a massa da Terra, orbitando os confins do nosso Sistema Solar, muito além da órbita de Plutão. Os cientistas inferiram sua presença, por meio de anomalias encontradas nas órbitas de seis objetos do chamado Cinturão de Kuiper.
O objeto, que os pesquisadores estão chamando de Planeta Nove, não chega muito perto do Sol, no ponto mais próximo da sua órbita ele fica a 30.5 bilhões de quilômetros, ou seja, cinco vezes a distância entre o Sol e Plutão. Apesar do seu grande tamanho, ele é muito apagado, e por isso ninguém até o momento conseguiu observá-lo.
Não existe ainda uma confirmação observacional da descoberta, mas as evidências são tão fortes que fizeram com que outros especialistas como Chad Trujilo do Observatório Gemini no Havaí e David Nesvorny, do Southwest Research Institute em Boulder no Colorado, ficassem impressionados e bem convencidos de que deve mesmo haver um grande planeta nas fronteiras da nossa vizinhança cósmica.
The document presents evidence for azimuthal variations in cosmic ray ion acceleration at the blast wave of the supernova remnant SN 1006. Using radio, X-ray, and optical observations, the researchers find that the ratio of radii between the blast wave and contact discontinuity varies azimuthally, being smallest in the brightest synchrotron emission regions, indicating more efficient cosmic ray acceleration. They interpret this as evidence that the injection rate, magnetic field strength, and turbulence level - which influence cosmic ray acceleration - all vary azimuthally and are highest in the brightest regions.
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.
1) High-dispersion spectroscopy was used to observe the young exoplanet Beta Pictoris b, detecting a blueshifted radial velocity of -15±1.7 km/s and rotational broadening of 25±3 km/s, indicating it spins faster than any planet in the solar system.
2) Beta Pictoris b's high spin velocity is consistent with an extrapolation of the trend of increasing spin velocity with planet mass seen in the solar system.
3) At an estimated age of 11±5 Myr, Beta Pictoris b is expected to cool and shrink over time, which would cause it to spin up further to a rotation velocity of around 40 km/s.
The document summarizes the effects of perturbations on satellite orbits due to the non-spherical shape and inhomogeneous mass distribution of Earth. It describes how Earth can be modeled using spherical harmonics and how the different terms (zonal, sectoral, tesseral) in the expansion affect the orbital elements like inclination, eccentricity, and longitude of satellites. While short-term changes may occur, the average values of semimajor axis and eccentricity remain constant. Long-term effects are seen in the right ascension of the ascending node, argument of perigee, and mean anomaly. The document provides mathematical expressions to describe these perturbations.
Artigo descreve a descoberta feita pelo Hubble de que duas luas de Plutão descrevem suas órbitas realizando cambalhotas imprevisíveis. Além disso, o estudo descobriu um link entre as órbitas das luas menores de Plutão.
Jupiter’s interior and deep atmosphere: The initial pole-to-pole passes with ...Sérgio Sacani
On 27 August 2016, the Juno spacecraft acquired science observations of Jupiter,
passing less than 5000 kilometers above the equatorial cloud tops. Images of Jupiter’s
poles show a chaotic scene, unlike Saturn’s poles. Microwave sounding reveals weather
features at pressures deeper than 100 bars, dominated by an ammonia-rich, narrow
low-latitude plume resembling a deeper, wider version of Earth’s Hadley cell. Near-infrared
mapping reveals the relative humidity within prominent downwelling regions. Juno’s
measured gravity field differs substantially from the last available estimate and is one
order of magnitude more precise. This has implications for the distribution of heavy
elements in the interior, including the existence and mass of Jupiter’s core. The observed
magnetic field exhibits smaller spatial variations than expected, indicative of a rich
harmonic content.
Jupiter’s magnetosphere and aurorae observed by the Juno spacecraft during it...Sérgio Sacani
The Juno spacecraft acquired direct observations of the jovian magnetosphere and auroral
emissions from a vantage point above the poles. Juno’s capture orbit spanned the jovian
magnetosphere from bow shock to the planet, providing magnetic field, charged particle,
and wave phenomena context for Juno’s passage over the poles and traverse of Jupiter’s
hazardous inner radiation belts. Juno’s energetic particle and plasma detectors measured
electrons precipitating in the polar regions, exciting intense aurorae, observed
simultaneously by the ultraviolet and infrared imaging spectrographs. Juno transited
beneath the most intense parts of the radiation belts, passed about 4000 kilometers
above the cloud tops at closest approach, well inside the jovian rings, and recorded the
electrical signatures of high-velocity impacts with small particles as it traversed the equator.
Similar to The dynamic geophysical environment of (101955) Bennu based on OSIRIS-REx measurements (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.
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.
ANAMOLOUS SECONDARY GROWTH IN DICOT ROOTS.pptxRASHMI M G
Abnormal or anomalous secondary growth in plants. It defines secondary growth as an increase in plant girth due to vascular cambium or cork cambium. Anomalous secondary growth does not follow the normal pattern of a single vascular cambium producing xylem internally and phloem externally.
The use of Nauplii and metanauplii artemia in aquaculture (brine shrimp).pptxMAGOTI ERNEST
Although Artemia has been known to man for centuries, its use as a food for the culture of larval organisms apparently began only in the 1930s, when several investigators found that it made an excellent food for newly hatched fish larvae (Litvinenko et al., 2023). As aquaculture developed in the 1960s and ‘70s, the use of Artemia also became more widespread, due both to its convenience and to its nutritional value for larval organisms (Arenas-Pardo et al., 2024). The fact that Artemia dormant cysts can be stored for long periods in cans, and then used as an off-the-shelf food requiring only 24 h of incubation makes them the most convenient, least labor-intensive, live food available for aquaculture (Sorgeloos & Roubach, 2021). The nutritional value of Artemia, especially for marine organisms, is not constant, but varies both geographically and temporally. During the last decade, however, both the causes of Artemia nutritional variability and methods to improve poorquality Artemia have been identified (Loufi et al., 2024).
Brine shrimp (Artemia spp.) are used in marine aquaculture worldwide. Annually, more than 2,000 metric tons of dry cysts are used for cultivation of fish, crustacean, and shellfish larva. Brine shrimp are important to aquaculture because newly hatched brine shrimp nauplii (larvae) provide a food source for many fish fry (Mozanzadeh et al., 2021). Culture and harvesting of brine shrimp eggs represents another aspect of the aquaculture industry. Nauplii and metanauplii of Artemia, commonly known as brine shrimp, play a crucial role in aquaculture due to their nutritional value and suitability as live feed for many aquatic species, particularly in larval stages (Sorgeloos & Roubach, 2021).
When I was asked to give a companion lecture in support of ‘The Philosophy of Science’ (https://shorturl.at/4pUXz) I decided not to walk through the detail of the many methodologies in order of use. Instead, I chose to employ a long standing, and ongoing, scientific development as an exemplar. And so, I chose the ever evolving story of Thermodynamics as a scientific investigation at its best.
Conducted over a period of >200 years, Thermodynamics R&D, and application, benefitted from the highest levels of professionalism, collaboration, and technical thoroughness. New layers of application, methodology, and practice were made possible by the progressive advance of technology. In turn, this has seen measurement and modelling accuracy continually improved at a micro and macro level.
Perhaps most importantly, Thermodynamics rapidly became a primary tool in the advance of applied science/engineering/technology, spanning micro-tech, to aerospace and cosmology. I can think of no better a story to illustrate the breadth of scientific methodologies and applications at their best.
Unlocking the mysteries of reproduction: Exploring fecundity and gonadosomati...AbdullaAlAsif1
The pygmy halfbeak Dermogenys colletei, is known for its viviparous nature, this presents an intriguing case of relatively low fecundity, raising questions about potential compensatory reproductive strategies employed by this species. Our study delves into the examination of fecundity and the Gonadosomatic Index (GSI) in the Pygmy Halfbeak, D. colletei (Meisner, 2001), an intriguing viviparous fish indigenous to Sarawak, Borneo. We hypothesize that the Pygmy halfbeak, D. colletei, may exhibit unique reproductive adaptations to offset its low fecundity, thus enhancing its survival and fitness. To address this, we conducted a comprehensive study utilizing 28 mature female specimens of D. colletei, carefully measuring fecundity and GSI to shed light on the reproductive adaptations of this species. Our findings reveal that D. colletei indeed exhibits low fecundity, with a mean of 16.76 ± 2.01, and a mean GSI of 12.83 ± 1.27, providing crucial insights into the reproductive mechanisms at play in this species. These results underscore the existence of unique reproductive strategies in D. colletei, enabling its adaptation and persistence in Borneo's diverse aquatic ecosystems, and call for further ecological research to elucidate these mechanisms. This study lends to a better understanding of viviparous fish in Borneo and contributes to the broader field of aquatic ecology, enhancing our knowledge of species adaptations to unique ecological challenges.
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
Comparing Evolved Extractive Text Summary Scores of Bidirectional Encoder Rep...University of Maribor
Slides from:
11th International Conference on Electrical, Electronics and Computer Engineering (IcETRAN), Niš, 3-6 June 2024
Track: Artificial Intelligence
https://www.etran.rs/2024/en/home-english/
Comparing Evolved Extractive Text Summary Scores of Bidirectional Encoder Rep...
The dynamic geophysical environment of (101955) Bennu based on OSIRIS-REx measurements
1. Articles
https://doi.org/10.1038/s41550-019-0721-3
1
Smead Department of Aerospace Engineering, University of Colorado, Boulder, CO, USA. 2
Jet Propulsion Laboratory, California Institute of Technology,
Pasadena, CA, USA. 3
KinetX Aerospace, Inc., Simi Valley, CA, USA. 4
NASA Goddard Space Flight Center, Greenbelt, MD, USA. 5
Aerospace Corporation,
Chantilly, VA, USA. 6
Department of Earth and Planetary Sciences, University of Tennessee, Knoxville, TN, USA. 7
School of Physical Sciences, The Open
University, Milton Keynes, UK. 8
Department of Aerospace Engineering, Auburn University, Auburn, AL, USA. 9
Colorado Center for Astrodynamics
Research, University of Colorado, Boulder, CO, USA. 10
JAXA Institute of Space and Astronautical Science, Sagamihara, Japan. 11
Planetary Science Institute,
Tucson, AZ, USA. 12
Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA. 13
Department of Earth, Ocean and Atmospheric Sciences,
University of British Columbia, Vancouver, British Columbia, Canada. 14
The Johns Hopkins University Applied Physics Laboratory, Laurel, MD, USA.
15
The Centre for Research in Earth and Space Science, York University, Toronto, Ontario, Canada. 16
Southwest Research Institute, Boulder, CO, USA.
17
Smithsonian Institution National Museum of Natural History, Washington, DC, USA. 18
Lockheed Martin Space, Littleton, CO, USA. 19
Université Côte
d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, Nice, France. 20
Department of Geology, Rowan University, Glassboro, NJ, USA.
21
A full list of authors and affiliations appears at the end of the paper. *e-mail: scheeres@colorado.edu
D
uring the Preliminary Survey phase of the OSIRIS-REx mis-
sion (between 3 and 19 December 2018), the OSIRIS-REx
spacecraft performed five slow, hyperbolic fly-bys of the near-
Earth asteroid (101955) Bennu, with closest approach distances of
about 7 km and speeds of about 4 cm s−1
. We tracked the spacecraft
using NASA's Deep Space Network to acquire Doppler shift data
that, combined with optical navigation images, detected the small
deflection of the spacecraft trajectory due to the asteroid’s gravity,
which was of the order of 3.5 cm s−1
(refs.1,2
) (see Methods). These
measurements yield a gravitational parameter of 4.892 ± 0.006 m3
s−2
(mass of 7.329 ± 0.009 × 1010
kg). By combining the mass with
the volume of 6.16 ± 0.07 × 107
m3
determined from the shape3
,
we determine a bulk density of 1,190 ± 13 kg m−3
. This bulk den-
sity is consistent with that of asteroid (162173) Ryugu, which was
measured to be 1,190 ± 30 kg m−3
by the Hayabusa2 team4
. On the
basis of an analogous CM chondrite, as discussed in ref. 3
, this den-
sity corresponds to a macroporosity of 40% to 50%, providing addi-
tional evidence that Bennu is a rubble-pile asteroid.
Our density estimate is consistent with the previous estimate of
1,260 ± 70 kg m−3
(refs. 5,6
), which was based on a detection of the
Yarkovsky effect using radar and infrared astronomy rather than
gravitational perturbations. We have refined that analysis using
the OSIRIS-REx shape model3
, thermal inertia values7
, and an
updated estimate of the Bennu ephemeris. The ephemeris update
includes spacecraft observations during the Approach phase of the
mission (17 August to 2 December 2018) and adjusts the semi-
major axis drift rate to (–19.020 ± 0.087) × 10−4
astronomical units
per million years, which is consistent with prior measurements5
.
The dynamic geophysical environment
of (101955) Bennu based on OSIRIS-REx
measurements
D. J. Scheeres 1
*, J. W. McMahon1
, A. S. French1
, D. N. Brack1
, S. R. Chesley2
, D. Farnocchia2
,
Y. Takahashi2
, J. M. Leonard3
, J. Geeraert3
, B. Page3
, P. Antreasian3
, K. Getzandanner4
, D. Rowlands4
,
E. M. Mazarico 4
, J. Small5
, D. E. Highsmith5
, M. Moreau4
, J. P. Emery6
, B. Rozitis7
, M. Hirabayashi8
,
P. Sánchez9
, S. Van wal 10
, P. Tricarico 11
, R.-L. Ballouz12
, C. L. Johnson11,13
, M. M. Al Asad13
,
H. C. M. Susorney13
, O. S. Barnouin 14
, M. G. Daly 15
, J. A. Seabrook 15
, R. W. Gaskell11
, E. E. Palmer 11
,
J. R. Weirich11
, K. J. Walsh 16
, E. R. Jawin17
, E. B. Bierhaus18
, P. Michel19
, W. F. Bottke16
, M. C. Nolan 12
,
H. C. Connolly Jr 20
, D. S. Lauretta12
and The OSIRIS-REx Team21
The top-shaped morphology characteristic of asteroid (101955) Bennu, often found among fast-spinning asteroids and binary
asteroid primaries, may have contributed substantially to binary asteroid formation. Yet a detailed geophysical analysis of
this morphology for a fast-spinning asteroid has not been possible prior to the Origins, Spectral Interpretation, Resource
Identification, and Security-Regolith Explorer (OSIRIS-REx) mission. Combining the measured Bennu mass and shape obtained
during the Preliminary Survey phase of the OSIRIS-REx mission, we find a notable transition in Bennu’s surface slopes within
its rotational Roche lobe, defined as the region where material is energetically trapped to the surface. As the intersection of
the rotational Roche lobe with Bennu’s surface has been most recently migrating towards its equator (given Bennu’s increasing
spin rate), we infer that Bennu’s surface slopes have been changing across its surface within the last million years. We also find
evidence for substantial density heterogeneity within this body, suggesting that its interior is a mixture of voids and boulders.
The presence of such heterogeneity and Bennu’s top shape are consistent with spin-induced failure at some point in its past,
although the manner of its failure cannot yet be determined. Future measurements by the OSIRIS-REx spacecraft will provide
insight into and may resolve questions regarding the formation and evolution of Bennu’s top-shape morphology and its link to
the formation of binary asteroids.
Nature Astronomy | www.nature.com/natureastronomy
2. Articles NATuRE ASTROnOmY
Applying the same model to fit the Yarkovsky drift rate using
these in situ measurements predicts a gravitational parameter of
4.9 ± 0.1 m3
s−2
, which agrees remarkably well with the direct mea-
surements. These results demonstrate that combining remote mea-
surements of shape, semi-major axis drift and thermal inertia is a
valid technique for determining the masses of asteroids.
Bennu’s geophysical and dynamical environment
Combining its mass, spin rate and shape (using a constant density
assumption), we evaluate the geophysical environment of Bennu,
repeating and refining the analysis made using pre-encounter
assumptions8
. The geopotential combines the gravitational potential
with the rotational potential in a Bennu-fixed frame to measure rel-
ative potential energy across the surface, and its gradient yields the
combined gravitational and centrifugal accelerations at any given
location in a frame rotating with Bennu. The maximum surface
acceleration is 80 µm s−2
at the poles and smoothly decreases across
the surface to the equator, where it reaches a minimum of 26 µm s−2
(Supplementary Fig. 1). Thus, material across the entire body exists
in a microgravity environment, a state that is poorly understood9
,
and where weak cohesive forces are comparable to gravitational and
friction forces10
. At the equator, the weight of a 1-m-radius boulder
will exert a pressure of about 0.1 Pa on the surface, and such a sur-
face cohesive strength would stabilize it against downslope motion.
The Bennu geopotential is highest at the poles and lowest at the
equator, meaning that all of the surface slopes are generally directed
toward the equatorial region (Fig. 1, Supplementary Fig. 2). Local
deviations from this trend occur across the surface and appear to
drive the local downslope motion of regolith11
. A particle rolling
downslope from either pole to the equator would acquire, at most,
just over 11 cm s−1
of speed if no energy were lost (Supplementary
Fig. 3). At the equator, the minimum rolling speed necessary for a
particle to leave the surface ranges from 2 cm s−1
to 4 cm s−1
, consid-
ering the local surface curvature and acceleration12
. Thus, material
can achieve orbit through downslope migration. This motivates the
study of dynamics close to the surface.
There are eight synchronous orbits about Bennu, locations where
an orbiting body will be stationary in the Bennu-fixed frame owing
to a balance between gravitational and centrifugal forces (Fig. 2).
The number of equilibrium points is consistent with the strong
degree-4 sectoral coefficients of the shape that creates a ‘square’
equatorial profile3
. These orbits lie less than 50 m from the surface
of Bennu, and their presence and stability properties control the
dynamics of any particles lofted from the equatorial region at low
speeds. For the current model, seven of these equilibria are unstable,
and one is stable—although its stability is very sensitive to small
details of the gravity field and shape, and so its stability determina-
tion may change. The presence of the unstable equilibrium points
creates a chaotic orbital environment in this region.
The geopotential also defines what we term Bennu’s ‘rotational
Roche lobe’, defined as the spatial surface where the geopotential has
the same value as the equilibrium point with minimum energy8
. The
lobe is thus the minimum-energy surface that separates Bennu from
space and intersects Bennu’s shape at average latitudes of –22.4° and
23.4°. The surface region between these latitudes lies within the lobe,
while the true intersection point varies by a few degrees in latitude
as a function of longitude, driven by the asteroid’s shape (Fig. 3).
Within this latitude band, any particles lofted with an energy less
than the rotational Roche lobe energy, which corresponds to speeds
of less than 4 cm s−1
, are trapped within the lobe; they cannot escape
from Bennu and will eventually re-strike the surface between these
latitudes (Supplementary Fig. 4). Conversely, speeds that place a par-
ticle directly on an escape trajectory range from more than 20 cm s−1
in the polar regions down to 10 cm s−1
in the equatorial region, and
are highly dependent on surface orientation (Supplementary Fig. 4).
Between these speeds, the outcome can be either re-strike, escape,
or capture into a longer-term stable orbit that could persist for days
to years. The range of orbits that can remain stable about Bennu
depends on particle size (which controls the strength of solar radia-
tion pressure) and ranges from centimetre-sized particles close to
the surface and in near-polar orbits, to larger bodies in equatorial
orbits out to its Hill sphere, which extends to 31 km (ref. 13
).
Surface slope distribution and the rotational Roche lobe
Surface slopes determined for Bennu are highly sensitive to the
resolution of the shape model used for analysis, as higher-resolu-
tion models start to capture the steep slopes of surface boulders.
However, the overall global structure of slope distributions on
x
z
x
y
y
z
x
z
y
z x
y
Slope(deg)
0
10
20
30
Fig. 1 | Global map of slope distributions across Bennu. The slope arrows show the direction of downslope motion with length scaled by the local slope
angle. The slopes are computed for a 3-m-resolution shape model, as this emphasizes the overall slope trends across the body, whereas higher-resolution
shape models would reflect the boulder morphology on the surface. The slopes are capped at 35°, with red regions going up to 46°.
Nature Astronomy | www.nature.com/natureastronomy
3. ArticlesNATuRE ASTROnOmY
Bennu are seen to have the same pattern independent of shape
resolution. For a 3-m-resolution shape model, the globally aver-
aged slopes are 15.4° (Fig. 1). The slope distribution shows a clear
transition that occurs at the rotational Roche lobe (Fig. 3), with the
surface within the lobe being more energetically relaxed than the
surface outside of the lobe. Within the rotational Roche lobe the
surface has an average slope of 11.8°, whereas latitudes outside of
the lobe have an average slope of 17.9° in the southern (–Z) and
18.8° in the northern (+Z) hemisphere. The dynamics associated
with the rotational Roche lobe may have contributed to the relaxed
slope within the lobe. For example, if there were a cloud of particles
orbiting about Bennu’s equator, some fraction of those particles
could be trapped within the lobe and would redistribute themselves
in this region, whereas those with greater energy or located out-
side the lobe would preferentially escape or enter longer-term stable
orbits. Also, particles, grains and boulders that migrate downslope
from the higher latitudes (where they otherwise have sufficient
energy to enter orbit) become trapped within the lobe once they
enter this region.
The latitudes of the lobe intersection are tied to the current spin
rate of the asteroid. This is important given the measured spin rate
acceleration described in Nolan et al14
. and updated in Hergenrother
et al.15
. Thus, a slower rotation rate in the past would lead to the
lobe having higher-latitude intersections. The surface relaxation
process may therefore be occurring concurrently with Bennu’s
changing spin rate. If this measured acceleration is due to the YORP
(Yarkovsky–O’Keefe–Radzievskii–Paddack) effect, defined as small
torques causing an asteroid’s spin rate to change and arising from
photons being scattered from asymmetries in its shape, it will dou-
ble Bennu’s spin rate in 1.5 million years (which defines Bennu’s
Roche lobe
Saddle points
Unstable centre points
Stable and unstable manifold trajectories
Stable centre points
x
y
x
z
Fig. 2 | Equilibrium points in the Bennu-fixed frame, shown with stable and unstable manifolds emanating from the unstable points, and showing a
stable trajectory in the vicinity of the stable equilibrium point. The manifolds control dynamical motion close to Bennu’s surface and create a chaotic
orbit environment that would redistribute lofted material. The rotational Roche lobe is also shown as the dark surface that emanates from the minimum-
energy equilibrium point and intersects with the surface of Bennu, shown with a pole-on view and a side view.
0
5
10
15
20
25
–80 –60 –40 –20 0 20 40 60 80
Latitude (deg)
Averageslope(deg)
Roche lobe intersections
Slope (deg)
x
z
a b
x
y x
y
0 10 20 30
17.9°
11.8°
18.8°
Fig. 3 | Surface slope distributions on Bennu in relation to the rotational Roche lobe. a, Slope distribution for a 3-m-resolution shape model of Bennu
showing the rotational Roche lobe intersection with the surface, marked with a thick black line. The slope transition is seen to closely follow the lobe
intersection region. b, Longitudinally averaged slope as a function of latitude, showing the average slopes within and outside the lobe. The averaging is over
1-degree-latitude bins, and thus at the average lobe transition latitude will capture some regions on the other side of the lobe. If the averaging is performed
exclusively within the lobe the average slope decreases to 11.7°, and the overall average slope outside of the lobe is 18.4°.
Nature Astronomy | www.nature.com/natureastronomy
4. Articles NATuRE ASTROnOmY
YORP timescale). If the observed increase in rotation rate persisted
linearly back in time, the asteroid was spinning with a 5-h period
450,000 years ago, putting the lobe intersection at ±49°, whereas
750,000 years ago the asteroid was spinning with an 8.6-h period,
putting the entire surface within the lobe.
This observation of a slope transition at the lobe boundary indi-
cates that the energetic trapping defined by the rotational Roche
lobe may play a part in controlling the shape and topography of the
surface. This is important given that all fast-spinning, top-shaped
asteroids will have similar intersections of their rotational Roche
lobes in their mid-latitudes. Such asteroids are commonly found
within the near-Earth asteroid population, and are the most fre-
quently found morphology for binary asteroid primaries (which
constitute about 15% of the near-Earth asteroid population)16
.
Binary primaries actually spin even faster than Bennu in general,
implying that they have an even narrower lobe about the equator,
which increases the likelihood that material can enter orbit and
leave the lobe, potentially forming binaries17–19
. Thus, our observa-
tion that the surface morphology follows the rotational Roche lobe
may also be an important clue linking binary formation to fast-spin-
ning, top-shaped asteroids.
Constraints on the origin of Bennu’s shape
Several formation mechanisms have been proposed for top-shaped
asteroids, and the OSIRIS-REx mission provides an opportunity to
probe and test these hypotheses. A direct interpretation of the sur-
face age of Bennu from crater density indicates an age of 100 mil-
lion to 1 billion years11
. Therefore, it is possible that the asteroid’s
distinctive shape was formed either during accretion20,21
or dur-
ing a reshaping event earlier in its history. However, a primordial
shape is inconsistent with the current slope transition at the lobe
intersection and the measured acceleration in its rotation period,
which suggests that Bennu’s surface changes in conjunction with
its rotation rate.
An early or initial shape formation could imply that Bennu has
avoided going through multiple YORP cycles—periods of more
rapid rotation due to YORP—which then lead to shape deforma-
tions and periods of slower rotation, with the sequence occurring
repetitively every few YORP timescales of 1.5 million years22,23
. The
avoidance of such YORP cycles could be explained if Bennu were
trapped in a YORP equilibrium for an extended period of time in
the main belt, in which there would be no change in its rotation state
and hence shape24
. Under this scenario, the asteroid may have been
disturbed only recently from this equilibrium, perhaps by its pas-
sage into the inner Solar System23
. Alternatively, it could imply that
our understanding of how rubble-pile bodies respond to periods of
rapid rotation is incomplete.
To study the implications of YORP evolution on Bennu’s shape,
we performed a stress analysis for faster spin rates25
. Figure 4 shows
the minimum cohesive strength needed to keep the body from
undergoing plastic deformation and the regions where it would
first fail in this way at different spin rates. At its current spin period
and up to 3.7 h, a cohesive strength of the order of 0.1 Pa or more is
needed to stabilize the surface against mass wasting. At spin periods
of 3.6 h and faster, a strength of 1 Pa or more is needed to stabilize
the interior. For context, recall that the weight of a 1 m boulder on
Bennu’s equator would exert a pressure of 0.1 Pa. A complementary
analysis of surface slopes (Fig. 4) shows that at spin periods below
3.6 h, over half of Bennu’s surface is at or exceeds an angle of repose
of 30° and would definitively fail via mass wasting if it were a cohe-
sionless regolith.
If Bennu acquired its distinctive shape after its initial forma-
tion, three main mechanisms have been proposed8
: formation by
downslope migration of material from mid-latitudes to the equa-
torial region26–28
; failure and collapse of the interior of the body,
deforming the surface of the asteroid25,29,30
; or the tidal disruption
of a natural satellite that fell back onto the asteroid surface31,32
. The
conformity of the slope change with the Roche lobe would be con-
sistent with this last scenario, as such an event would distribute a
large amount of material across the equator at low speeds, which
would preferentially settle within the lobe. As this would be a one-
time event, it seems inconsistent with the age of the surface and the
current acceleration of the spin rate, however.
An interior failure could have occurred in the past, and gran-
ular mechanics simulations show that if the interior had bulged
outwards, surface structures could have been maintained without
Slope (deg)Fractionofsurfaceatgivenslope
4.3 hr
0.2 Pa
3.9 hr
0.2 Pa
3.7 hr
0.3 Pa
3.5 hr
1.0 Pa
3.3 hr
1.25 Pa
3.0 hr
2.5 Pa
Latitude (deg)
Averageslope(deg)
3.6 hr
0
5
10
15
20
25
30
35
–80 –60 –40 –20 0 20 40 60 80
a b
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0 10 20 30 40 50 60 70
Spin period = 4.29 h
3.60 h
3.40 h
30°
Fig. 4 | Failure patterns as a function of Bennu spin rates. a, Shape stability maps showing regions of elastic deformation (green) and plastic deformation
(yellow) with arrows showing the direction of deformation at different spin periods and strengths. Under a uniform density and strength distribution
assumption, Bennu requires less than 0.3 Pa of strength to retain surface stability up to a spin period of 3.7 h. At faster spin periods, failure occurs across
the interior of the body, and Bennu requires a strength of at least 1 Pa to maintain its current shape. b, The surface slope distribution has its accumulation
point at around 3.6 h, beyond which the majority of the surface is beyond the usual 30° angle of repose for cohesionless material28
. The inset shows the
average slope as a function of latitude at a 3.6-h spin period.
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5. ArticlesNATuRE ASTROnOmY
deformation (see Methods), implying that even a more recent
interior failure mode such as this could be feasible and consistent
with an old surface. This failure mode would predict a less dense
interior as compared to our measured bulk density25,30
, and would
correspond to gravity coefficients that are larger than the shape-
based constant density gravity coefficients. If, instead, the interior
strength were sufficient to prohibit that failure mode, then the man-
tle of surface material would fail at a fast spin rate28
. Comparison of
the surface slope distribution at past plausible spin rates shows that
the current surface is consistent with failure at a spin rate of 3.6 h
(Fig. 4) and yields a shape that is consistent with this failure mode
(Fig. 5)19,27
. These findings support the possibility of a denser core,
with corresponding lower values of gravity coefficients.
Density heterogeneity within Bennu
These hypotheses show the importance of constraining the inter-
nal density distribution of Bennu. We can explore this by analysing
Bennu’s shape model, which is constructed such that its origin is
at the centre of mass and that it spins about its maximum moment
of inertia. Under a constant density assumption, the offset between
the centre of figure and centre of mass is [1.4, –0.5, –0.15] m in
the Bennu-fixed frame. The corresponding products of inertia are
Izx = − 46.70 m2
and Izy = 11.39 m2
, as compared to its predicted
maximum moment of inertia Izz = 26,780 m2
(refs. 3,33
). These mea-
surements correspond to a about 0.1% shift in the centre of mass
and an approximately 0.1° offset of the principal axis with respect
to a constant density shape, and they indicate heterogeneity in the
mass distribution. To account for this heterogeneity with a simple
(but non-unique) model consistent with surface observations and
Bennu’s rubble-pile structure, we assume that Bennu contains two
spherical boulders with a particle density twice the measured bulk
density (assuming a 50% porosity) and diameters of 80 m (less than
the largest boulder outcrop size seen on Bennu7,11
). These objects
would constitute almost 1% of the total mass and would have a
density of 2,360 kg m−3
with the bulk density of the remaining body
at 1,180 kg m−3
. To match the observed asymmetry, both boulders
must be displaced in the –x direction, with one of them having
its largest extent at the surface, and with both bodies displaced in
opposite directions about the equatorial plane with a total separa-
tion between them of 200 m (see Methods, Supplementary Fig. 5).
Although this solution is not unique, it establishes that the neces-
sary inhomogeneities are significant, but can be explained in a plau-
sible model.
OSIRIS-REx’s future low orbits about Bennu will refine our
understanding of the surface and enable us to estimate higher-order
gravity field coefficients. These measurements will increase the
resolution at which we can detect and constrain Bennu’s internal
heterogeneities and will provide direct evidence of how the mass is
distributed within the body. This, in turn, will enable us to evaluate
the competing theories for how its shape formed, or may suggest
alternative models to consider. They will also shed additional light
on the connections between Bennu’s apparent migration of its sur-
face slopes, pathways to the formation of top-shaped asteroids and
ultimately provide insights into binary formation.
Methods
Shape model. The results in this paper were computed using the v14 shape model,
as defined in Barnouin et al.3
.
Mass measurement and estimation. The Bennu mass measurement experiment
carried out by the OSIRIS-REx mission involved several teams each using unique
combinations of software tools and data-processing techniques. The radio science
teams were based at the University of Colorado in the Colorado Center for
Astrodynamics Research and at the Jet Propulsion Laboratory. The navigation and
flight dynamics teams were represented by the KinetX Corporation with a team
in residence at Lockheed Martin’s Waterton Campus in Denver and a team at the
Goddard Space Flight Center. The mass estimates and other fitting data from each
team were compared and found to converge to the same mass value within the
expected errors. The specific value quoted in the paper is from the University of
Colorado estimate; however, all other estimates agreed with this value to within the
quoted error estimates as of early January 2019.
The OSIRIS-REx spacecraft began the Approach phase towards asteroid Bennu
on 17 August 2018. During Approach the spacecraft performed six manoeuvres to
decelerate the spacecraft with respect to Bennu and place it at the starting location
of the Preliminary Survey phase on 3 December 2018. The Preliminary Survey
phase consisted of five fly-bys—three over the north pole, one over the equator and
one over the south pole—and two transition legs. Each fly-by started approximately
18.5 km from Bennu, took 48 h to complete, and achieved a closest approach
of 7.5 km at the 24 h mark. The polar fly-bys were along the terminator and the
equatorial fly-by was on the sunlit side. All fly-by and transition arcs were joined
by manoeuvres that varied between 20 cm s−1
and 40 cm s−1
.
Images taken by spacecraft cameras (PolyCam, MapCam, NavCam1)34
were
used to generate centre-finding optical navigation data35
. Optical navigation images
were taken between 3 and 7 times per week during Approach and every 2 h during
Preliminary Survey. These data, along with the ‘X-band two-way Doppler’ data
and the ’two-way range and delta-differential one-way range’ data from the
Deep Space Network, were used to determine both the spacecraft trajectory and
Bennu’s ephemeris.
Solution methods summaries. Radio science team. The University of Colorado
radio science orbit determination solutions were computed using the Jet
Propulsion Laboratory’s Mission Analysis, Operations and Navigation Toolkit
–0.3
–0.2
–0.1
0
0.1
0.2
0.3
–0.3 –0.2 –0.1 0 0.1 0.2 0.3
Latitude (deg)
Averageradius(km)
0.260 km
0.235 km 0.235 km
0.246 km
0.2
0.21
0.22
0.23
0.24
0.25
0.26
0.27
0.28
0.29
0.3
–80 –60 –40 –20 0 20 40 60 80
a b
Equatorial axis (km)
Polaraxis(km)
Fig. 5 | The averaged Bennu shape shows global characteristics associated with a landslide failure. a, The longitudinally averaged Bennu radius as a
function of latitude, shown in purple. The green line is the globally averaged radius and the black lines are the averages inside and outside the rotational
Roche lobe. b, Bennu’s shape profile (purple line) compared with its average radius (blue). The smaller radius at mid-latitudes, pole radii close to the mean
radius and the exuded equator constitute a predicted profile for a global surface landslide19
.
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6. Articles NATuRE ASTROnOmY
Environment (MONTE)36
. The two-way Doppler and two-way range data were
weighted per pass and per antenna at twice their observed noises to prevent over-
fitting to imperfectly calibrated data. Per-pass range biases were estimated with an
a priori uncertainty of 10 range units, where 7.022 range units = 1 m. The delta-
differential one-way range data was weighted at 0.06 ns, the recommended value
provided by the Deep Space Network. The optical centre-finding sample and line
were weighted at 0.5 pixels on Approach and de-weighted to 2.0 pixels during the
Preliminary Survey phase to account for the increase in Bennu’s apparent diameter.
Non-gravitational perturbations to the spacecraft trajectory were characterized
prior to the start of the Preliminary Survey in order to minimize aliasing between
solar pressure, stochastic accelerations and gravitational parameter. Area scale
factors for each of the Sun-facing plates were estimated on Approach to account
for solar pressure and thermal radiation mis-modelling. The plate areas were then
held fixed during Preliminary Survey and a single solar pressure scale factor was
estimated. Stochastic accelerations were estimated in 12-hour batches with an a
priori uncertainty of 5 × 10−13
km s−2
. Owing to the regular cadence of the fly-by/
manoeuvre cycle, the stochastic accelerations were correlated exponentially
with a 3-day time constant after manoeuvre M1P to prevent interplay with the
gravitational parameter and the manoeuvres. In addition to these, parameters
estimated in the solution included the spacecraft state at epoch, the Bennu
ephemeris, momentum wheel desaturation manoeuvres, targeting manoeuvre
thrust and pointing, per-pass range biases and the Bennu gravitational parameter.
The final reconstructed uncertainty for the spacecraft’s Bennu-relative state
averaged approximately 5 m in position and 0.2 mm s−1
in velocity for each
axis, with an uncertainty of 3-sigma. Solutions were generated for various data
weights, stochastic uncertainties, batch lengths and correlation times. It was
noted that the gravitational parameter trended lower with tighter radio weights
or larger stochastic uncertainty, but all solutions produced both trajectories and
gravitational parameters consistent to the 1-sigma level.
The Jet Propulsion Laboratory estimation setup is similar, and more details can
be found in ref. 37
KinetX. The OSIRIS-REx navigation team’s best-estimate of the Bennu gravitational
parameter following the Preliminary Survey phase is 4.89 ± 0.006 (1-sigma) m3
s−2
.
Extensive work went into modelling the spacecraft down to the acceleration
level of 1.0 × 10–13
km s−2
level going into the first north pole fly-by of Bennu.
Throughout the cruise, the approach taken by the OSIRIS-REx orbit determination
team was to model every deterministic acceleration using physics-based models.
No non-physical scaling of the solar radiation pressure was used. A 10-plate
box-wing model was used for the spacecraft with measured areas obtained from
pre-launch three-dimensional models. Documentation from Lockheed Martin
and close-out photographs of the spacecraft in flight configuration were used to
determine the material covering of each surface as well as the specular and diffuse
reflectivity coefficients. Coordination with the Lockheed Martin thermal team
provided a detailed thermal re-radiation model of the spacecraft surfaces for the
10-plate model as well as the addition of the radiators located on the –Z deck of the
spacecraft. The model developed with the Lockheed Martin thermal team spanned
predicted temperatures for each panel over various solar distances and off-Sun
angles. This approach was taken because the passive Lambertian assumption for
diffuse radiation of the surfaces did not accurately model the thermal re-radiation
effects as seen from an active spacecraft. This thermal re-radiation model along
with the estimation of the specular and diffuse re-radiation coefficients of the
10-plate solar radiation pressure model produced a model that matched the
pre-launch surface properties and acceleration accuracies to less than 0.5% of
the solar radiation pressure acceleration. This model continuously predicted the
approach trajectory to less than 1-sigma of the predicted trajectory uncertainties
with random fluctuations in estimated stochastic accelerations of the order of
0.5 × 10–13
km s−2
1-sigma. These additional estimated accelerations were correlated
with increased spacecraft activities and off-nominal attitude orientations not seen
during cruise.
In addition to the solar radiation pressure and thermal modelling, the orbit
determination team was able to estimate discrepancies between the internal
electronic path delays provided pre-launch and what was continuously seen in
flight. Coordination with the telecommunications team provided corrections
to the radiometric data based on the location of the antenna phase-centre
offsets. All antenna phase-centre offsets were estimated in flight during slewing
activities to confirm the pre-launch provided locations. All ground station and
Earth Orientation Parameters corrections were updated to coincide with those
recommended by the International Earth Rotation and Reference Systems Service
2010 conventions. Ground station locations are corrected based on solid tides,
pole tides, ocean tides, polar motion and continental drift. An acceleration
correction due to the electromagnetic radiation pressure of the high-gain and
low-gain antennas as well as the OSIRIS-REx Laser Altimeter was modelled
throughout Approach.
The orbit determination team estimated the spacecraft state, finite manoeuvres,
desaturation manoeuvres, per-pass range biases, Bennu ephemeris, stochastic
un-modelled accelerations and solar radiation pressure scaling. Radiometric data
of the 2-way range and Doppler data, the delta-differential one-way range data
and the optical images using Gaussian two-dimensional fitting, phase corrections
and cross-correlation limb-fitting techniques were the primary source of the
observables processed. Prior to the initial Preliminary Survey north pole fly-by,
the navigation team trended the estimated solution parameters. No stochastic
accelerations were estimated after the first Preliminary Survey flyby. This was done
to make sure no soak-up parameters masked the gravity signal during the fly-bys.
Goddard Space Flight Center. Members of the flight dynamics team located at
the NASA Goddard Space Flight Center generated an independent spacecraft
trajectory solution and Bennu gravitational parameter estimate at the end of the
Preliminary Survey phase. This solution used the GEODYN orbit determination
and geophysical parameter estimation software package, also developed and
maintained at the Goddard Space Flight Center38
.
The Goddard Space Flight Centersolution included Deep Space Network
radiometric (sequential range, Doppler and delta-differential one-way range)
and centre-finding optical navigation measurement types. The centre-finding
measurements were constructed by processing MapCam and NavCam images in
the Goddard Image Analysis and Navigation Tool (GIANT)39
. GIANT uses stars
in adjoining long-exposure images to provide precise absolute (inertial) pointing
information interpolated to the epoch of short-exposure images containing Bennu’s
full extent. The centre of Bennu in the image is determined precisely through two-
dimensional cross-correlation of Bennu’s illuminated shape in the image along with
a rendered template of the estimated shape model. The model used for Preliminary
Survey was constructed by OSIRIS-REx Altimetry Working Group member Robert
Gaskell using stereophotoclinometry40
based on Approach PolyCam imagery and
delivered on 27 November 2018. The measurement data weights for the Deep
Space Network’s sequential range measurements were 21 range units, for the Deep
Space Network’s 2-way Doppler data were 5.5 mHz, for the Deep Space Network’s
delta-differenced one-way range data were 0.06 ns, and for the optical navigation
centre-finding were 1 pixel. Direct altimetry data from the OSIRIS-REx Laser
Altimeter41
taken during four of the Preliminary Survey fly-bys were processed
along with the other measurement data types but not included in the final solution.
The final Preliminary Survey arc started on 3 December and ended on
24 December. A summary of the estimated parameter list included the spacecraft
and asteroid epoch states, the Bennu gravitational parameter, spacecraft
manoeuvres and momentum wheel desaturations, 3-axis stochastic accelerations
with a priori uncertainties of 1 nm s−2
and per-pass range biases with 2-metre a
priori uncertainty. Force modelling included point mass gravitation (the Sun,
eight planets and Pluto), Bennu non-spherical gravity (15 × 15 assuming uniform
density), 11-plate solar radiation pressure, spacecraft thermal radiation and
stochastic accelerations. Temperatures for the thermal radiation model were
provided by the spacecraft team at Lockheed Martin as originally requested
by KinetX Aerospace. Reconstructed spacecraft attitude and panel orientation
information was also provided by the spacecraft team. In addition to the
integration and estimation of the OSIRIS-REx trajectory, the orbit of Bennu itself
is concurrently integrated and estimated as well. The a priori initial state and fully
correlated covariance for Bennu was obtained from the OSIRIS-REx Radio Science
Working Group and the Jet Propulsion Laboratory Group (Solution 103, delivered
8 November 2018)37
. All spacecraft manoeuvres (M2P through to M1A) were
modelled as impulsive ΔVs with a priori values and uncertainties provided by the
spacecraft team via ‘manoeuvre implementation files’. Initial values for spacecraft
momentum desaturations were derived from the number of pulse counts provided
in the ’small forces file' and trending data since launch.
Density heterogeneity constraint computations. To develop a simple yet
physically feasible model to fit the non-zero centre of mass and product of
inertia information with a density distribution we implement the following
algorithm and approach.
Density. Assuming a 50% macroporosity, we consider mass contributions to
be twice the bulk density. We note that this is equivalent—but opposite—to
introducing zero density voids into the body.
Size. The largest body observed on Bennu is at most 80 m in diameter
(one dimension). Taking this as a limiting value, we choose boulders of
80 m in diameter. Using a smaller size will require the masses to be pushed
farther from the centre of the asteroid. This sets the masses of the two boulders
and yields the following.
The mass fractions of the shape and individual grains are 0.9914 and
0.0043, respectively, and are defined as the mass of the component over the
total mass. Bulk densities of the shape and individual grains are 1,178 kg m−3
and 2,356 kg m−3
, respectively.
Constraints. The centre of mass provides three constraints that need to be satisfied
by the grain locations, captured in a single vector equation:
+ + =M r M r M r 00 COF 1 1 2 2
where the 0 subscript represents the main body, the subscript COF represents
‘centre of figure’, and the subscripts 1 and 2 represent the two bodies, respectively.
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7. ArticlesNATuRE ASTROnOmY
The products of inertia, assuming mass-normalized values, provide two
additional equations:
− −M I M x z M x zxz0 1 1 1 2 2 2
− − =M I M y z M y z 0yz0 1 1 1 2 2 2
The system as specified is over-constrained, with six free variables (position vectors
of each body) and five constraints. To reduce this we introduce an additional
constraint, forcing the boulders to have a fixed relative offset in the z-coordinate:
− − Δ =z z z Z 02 1 1
where ΔZ is a free, dimensionless parameter. If it is greater than –1 the two
masses are on the same side of the equator; if equal to –1 then both are zero
(meaning that a z-component in the centre of mass cannot be accommodated); and
if less than –1 then they are on opposite sides. With this constraint we can then
solve for the z-components as:
=
+ + Δ
z
M z
M M M Z1
0 0
1 2 2
=
+ Δ
+ + Δ
z
Z M z
M M M Z
(1 )
2
0 0
1 2 2
and then solve the resulting linear equations for the x–y components to find:
= −
−
− +x
M
M z z
I x z x z
( )
[ ]xy1
0
1 2 1
0 0 0 2
=
−
− +x
M
M z z
I x z x z
( )
[ ]xz2
0
2 2 1
0 0 0 1
= −
−
− +y
M
M z z
I y z y z
( )
[ ]yz1
0
1 2 1
0 0 0 2
=
−
− +y
M
M z z
I y z y z
( )
[ ]yz2
0
2 2 1
0 0 0 1
Finally, to choose the nominal values we vary the parameter ΔZ over the
interval (–1.86, –1.96) to find locations that are nominally within Bennu. The value
used in the paper is –1.9, which places the outermost of these points deepest within
the body, allowing its 40-m radius to lie just at the surface. Supplementary Fig. 5
shows this plotted on top of the average radius shape model.
Bennu’s geophysical environment computations and supporting results. The
methods and supporting documentation on how the geophysical environment
items were computed is summarized and presented in greater detail in ref. 42
.
When applied to the current estimate of the Bennu shape, mass and spin state this
yields computations of the surface acceleration, the surface geopotential energy,
the return speed, the escape speed and the slopes and slope directions. With the
exception of the slope, these computations all appear similar to that reported to the
pre-arrival model, albeit now with definite values. These are presented below with
some notes. The computation of the lift-off speed applies the formulae defined in
ref. 12
to a polyhedral surface as outlined in ref. 43
.
Equilibrium point computation and characterization. The Bennu equilibrium
points are computed following the algorithm in ref. 44
and their stability evaluated
as described in ref. 42
. Bennu is found to have eight synchronous orbits close to its
surface. Four of these are hyperbolically unstable saddle points, while the other
four are centre equilibrium points and can be either stable or unstable. For the
current model three of these centre equilibria are unstable and one is stable (Fig. 2).
The presence of a stable equilibrium point implies that there is a zone about the
body where particles, if placed appropriately, can remain in orbit indefinitely about
a region in the body-fixed frame. This stable equilibrium point has three distinct
oscillation frequencies, two in-plane with periods of 5.8 h and 8.6 h, and one out-
of-plane with a period of 3.9 h. The stability of this point is sensitive to the detailed
gravity field of the asteroid, and thus may be updated once higher-order gravity
field coefficients are estimated.
The remaining equilibria are hyperbolically unstable, with characteristic times
for the saddle points ranging from 1 to 1.4 h and 2.6 to 3.4 h for the unstable centre
points. All have stable out-of-plane oscillations with periods around 3.9 h. We
denote the dynamical region in the vicinity of the equator as chaotic based on these
stability determinations. This designation is appropriate as the expected presence
of heteroclinic tangles associated with these equilibrium points (specifically,
associated with manifolds from periodic orbits and quasi-periodic orbits in their
vicinity) creates a chaotic orbital environment for any material lifted from the
surface at low speeds.
Rotational Roche lobe computation. The rotational Roche lobe is found by
finding the lowest geopotential energy of the eight equilibrium points, which
turns out to be the one that lies close to the positive x-axis. Given this Roche lobe
energy, we adjust the radii of a chosen shape model until the point reaches this
energy value, computed with a relative precision of 10−5
. Vertices that are within
1 m of the surface are considered to be locations where the lobe is intersecting
the asteroid surface, and are plotted as black points in Fig. 3. This computation is
independent of the slope computations, meaning that transitions seen in the figure
are not adjusted in any way, and represent the true variation. To compute the lobe
at different spin periods, the entire process is repeated, including finding the new
equilibrium points.
Stress and deformation analysis of Bennu. The methodology for computing
the stress and failure analysis of Bennu is outlined in ref. 29
. The computations
assume a uniform density and strength distribution, and an angle of friction
of 35°. The computations were carried out using ANSYS Mechanical APDL
(17.0) on the Auburn University Hopper supercomputing system. Additional
runs were made that varied the internal density—for both a higher and a
lower density—but did not produce any substantial deviation in the necessary
strengths or spin periods at failure. Future analysis will use more detailed maps
of internal density distribution to probe the asteroid failure state resulting from
periods of high rotation.
To probe the effect of an internal deformation on the surface regolith, the
granular mechanics model outlined in ref. 18
was applied to a representative
longitude lune, starting at a spherical shape and distorting it into an equatorial
bulge to mimic the Bennu ridge. For both cohesionless and cohesive grains we
did not observe much distortion of the surface material on the equator, consistent
with features on the surface potentially being retained during a period of shape
deformation owing to internal failure. Distortion of the surface close to the pole,
however, seems to be related to the violence of the reshaping and the strength of
the regolith.
To analyse the global shape and trends across the surface, the slope and radius
of Bennu was averaged over longitude within latitude bands of 1°. To perform
these averages all facets with a centroid within a given latitude interval were
identified, and the quantity of interest was multiplied by the differential area of
the latitude band (computed at the local radius value) and summed, in effect
performing an average across the longitude of the asteroid. This quantity was then
divided by the summed total area of these regions, performing an area-normalized
average of the quantity. The averages were performed across the 3-m resolution
shape model, which has about 200,000 facets, providing on average over 1,000
facets per latitude bin.
Code availability
ANSYS Mechanical APDL is commercially available (https://www.ansys.com/
services/training-center/structures/introduction-to-ansys-mechanical-apdl).
Data availability
The data that support the plots within this paper and other findings of this study
are available from the corresponding author upon reasonable request. Spacecraft
tracking data and ancillary files will be available via the Planetary Data System
(PDS) (https://sbn.psi.edu/pds/resource/orex/). Data are delivered to the PDS
according to the OSIRIS-REx Data Management Plan available in the OSIRIS-REx
PDS archive. Higher-level products, for example, slope maps, will be available in
the PDS one year after departure from the asteroid.
Received: 29 January 2019; Accepted: 11 February 2019;
Published: xx xx xxxx
References
1. McMahon, J. W. et al. The OSIRIS-REx radio science experiment at Bennu.
Space Sci. Rev. 214, 43 (2018).
2. Williams, B. et al. OSIRIS-REx flight dynamics and navigation design. Space
Sci. Rev. 214, 69 (2018).
3. Barnouin, O. S. et al. Shape of (101955) Bennu indicative of a rubble pile
with internal stiffness. Nat. Geosci. https://doi.org/10.1038/s41561-019-0330-x
(2019).
4. Watanabe, S. et al. Hayabusa2 arrives at the carbonaceous asteroid 162173
Ryugu — a spinning-top-shaped rubble pile. Science https://doi.org/10.1126/
science.aav8032 (in the press).
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(101955) Bennu. Icarus 235, 5–22 (2014).
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9. ArticlesNATuRE ASTROnOmY
The OSIRIS-REx Team
D. E. Highsmith5
, J. Small5
, D. Vokrouhlický22
, N. E. Bowles23
, E. Brown23
, K. L. Donaldson Hanna23
,
T. Warren23
, C. Brunet24
, R. A. Chicoine24
, S. Desjardins24
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Catholic University of America, Washington, DC, USA. 26
Center for Astrophysics, Harvard
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City University of New York, New York,
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Department of Astronomy, Cornell University, Ithaca,
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Department of Astronomy, University of Maryland, College Park, MD, USA. 35
Department of Earth and Planetary Sciences, University of
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Department of Earth Sciences, University of Toronto, Toronto, Ontario, Canada. 37
Department of Earth, Atmospheric,
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Department of Geography, University of Winnipeg, Winnipeg,
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Department of Geosciences,
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Department of Physics and Astronomy, Ithaca College, Ithaca, NY, USA. 44
Department of Physics and
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Institut
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Jacobs Technology, Houston, TX, USA.
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NASA Marshall Space Flight Center, Huntsville, AL, USA.
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Royal Ontario Museum, Toronto,
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School of Earth and Planetary Sciences, Curtin University, Perth, Western Australia, Australia. 75
School of Earth and Space Exploration,
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SETI Institute, Mountain View, CA, USA. 77
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Space Science
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Space Systems Laboratory, Department of Aeronautics and Astronautics, Massachusetts Institute of Technology, Cambridge,
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US Geological Survey Astrogeology Science Center, Flagstaff, AZ, USA. 81
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