- NASA's OSIRIS-REx mission arrived at the near-Earth asteroid Bennu in December 2018 and obtained images revealing its shape and surface features.
- Bennu has a diameter of 492 meters and is classified as a rubble pile asteroid, consisting of loosely bound fragments with high porosity.
- Images show numerous large boulders on Bennu's surface, some over 50 meters in size, indicating impacts in its past. Fractured boulders and impact breccias further suggest a dynamic history.
- The surface shows signs of both ancient features from the main asteroid belt as well as more recent mass movement, with clusters of boulders in low areas and incomplete crater
The 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.
Properties of rubble-pile asteroid (101955) Bennu from OSIRIS-REx imaging and...Sérgio Sacani
This document summarizes findings from imaging and thermal analysis of asteroid Bennu by NASA's OSIRIS-REx spacecraft. It finds that Bennu's surface is globally rough, dense with boulders over 1 meter in size, and has a low albedo of 4.4%. Thermal data indicates a moderate global thermal inertia of 350 J m-2 K-1 s-1/2, suggesting surface particle sizes of 0.5-5 cm by simple models, however images show the surface is dominated by boulders over 1 meter. Over 80% of the surface was analyzed, finding a power law distribution of boulder sizes with an index of -2.9 for boulders 8 meters
1. The document discusses the scientific discoveries that led to the development of the theory of seafloor spreading in the 1960s. These included findings that the ocean floor is much younger than originally thought, gets older further from mid-ocean ridges, and displays magnetic banding patterns that can be explained by the flipping of Earth's magnetic field during volcanic eruptions.
2. Harry Hess and Robert Dietz independently developed the theory of seafloor spreading to explain these patterns, proposing that new crust is formed at mid-ocean ridges and spreads laterally over time.
3. Vine and Matthews combined the theory of seafloor spreading with the hypothesis
Engineering Geology - The structure of the earth - Lecture SummaryAhmed Nassar
The document summarizes key concepts about the structure and layers of the Earth. It discusses that the main layers are the crust, mantle, and core. The crust is the thinnest layer and is divided into tectonic plates that move via processes at plate boundaries. The mantle makes up most of the Earth's volume and is composed of hot, convecting rock. At the center is the core, with a solid inner core and liquid outer core that generates the Earth's magnetic field.
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.
This document summarizes the current understanding of the assembly and break-up of the late Neoproterozoic supercontinent Rodinia based on geological, geochronological, and paleomagnetic evidence. Key points include:
- Rodinia assembled between 1300-900 Ma through worldwide orogenic events involving nearly all continental blocks. It lasted around 150 million years before breaking up.
- Laurentia is considered the core of Rodinia, with other continents proposed to have been located along its margins. However, the configurations of these continental connections remain controversial.
- The break-up of Rodinia occurred diachronously between ca. 825-740 Ma, associated with episodic mantle plume events
In situ radiometric_and_exposure_age_dating_of_the_martian_surfaceSérgio Sacani
The document summarizes research on the Sheepbed mudstone sample collected by the Curiosity rover in Gale crater on Mars. Key points:
- Potassium-argon dating of the mudstone yielded an age of 4.21 ± 0.35 billion years, consistent with the expected antiquity of rocks in Gale crater.
- Cosmogenic neon-21, helium-3, and argon-36 isotopes in the mudstone yielded concordant surface exposure ages of 78 ± 30 million years, indicating recent exposure by wind erosion rather than during initial transport and deposition.
- The mudstone's composition and mineralogy suggest it has not been heated above 200°C and may preserve
The GRAIL spacecraft measured the gravity field of the Moon at high resolution, allowing determination of the bulk density and porosity of the lunar crust. The analysis found:
1) The bulk density of the lunar highlands crust is 2550 kg/m3, substantially lower than previous estimates due to impact-induced porosity.
2) The average porosity of the crust is 12%, varying regionally from 4-21% and correlated with impact basins.
3) A new global crustal thickness model was constructed satisfying seismic constraints with an average thickness of 34-43 km, indicating the Moon's composition is not highly enriched compared to Earth.
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.
Properties of rubble-pile asteroid (101955) Bennu from OSIRIS-REx imaging and...Sérgio Sacani
This document summarizes findings from imaging and thermal analysis of asteroid Bennu by NASA's OSIRIS-REx spacecraft. It finds that Bennu's surface is globally rough, dense with boulders over 1 meter in size, and has a low albedo of 4.4%. Thermal data indicates a moderate global thermal inertia of 350 J m-2 K-1 s-1/2, suggesting surface particle sizes of 0.5-5 cm by simple models, however images show the surface is dominated by boulders over 1 meter. Over 80% of the surface was analyzed, finding a power law distribution of boulder sizes with an index of -2.9 for boulders 8 meters
1. The document discusses the scientific discoveries that led to the development of the theory of seafloor spreading in the 1960s. These included findings that the ocean floor is much younger than originally thought, gets older further from mid-ocean ridges, and displays magnetic banding patterns that can be explained by the flipping of Earth's magnetic field during volcanic eruptions.
2. Harry Hess and Robert Dietz independently developed the theory of seafloor spreading to explain these patterns, proposing that new crust is formed at mid-ocean ridges and spreads laterally over time.
3. Vine and Matthews combined the theory of seafloor spreading with the hypothesis
Engineering Geology - The structure of the earth - Lecture SummaryAhmed Nassar
The document summarizes key concepts about the structure and layers of the Earth. It discusses that the main layers are the crust, mantle, and core. The crust is the thinnest layer and is divided into tectonic plates that move via processes at plate boundaries. The mantle makes up most of the Earth's volume and is composed of hot, convecting rock. At the center is the core, with a solid inner core and liquid outer core that generates the Earth's magnetic field.
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.
This document summarizes the current understanding of the assembly and break-up of the late Neoproterozoic supercontinent Rodinia based on geological, geochronological, and paleomagnetic evidence. Key points include:
- Rodinia assembled between 1300-900 Ma through worldwide orogenic events involving nearly all continental blocks. It lasted around 150 million years before breaking up.
- Laurentia is considered the core of Rodinia, with other continents proposed to have been located along its margins. However, the configurations of these continental connections remain controversial.
- The break-up of Rodinia occurred diachronously between ca. 825-740 Ma, associated with episodic mantle plume events
In situ radiometric_and_exposure_age_dating_of_the_martian_surfaceSérgio Sacani
The document summarizes research on the Sheepbed mudstone sample collected by the Curiosity rover in Gale crater on Mars. Key points:
- Potassium-argon dating of the mudstone yielded an age of 4.21 ± 0.35 billion years, consistent with the expected antiquity of rocks in Gale crater.
- Cosmogenic neon-21, helium-3, and argon-36 isotopes in the mudstone yielded concordant surface exposure ages of 78 ± 30 million years, indicating recent exposure by wind erosion rather than during initial transport and deposition.
- The mudstone's composition and mineralogy suggest it has not been heated above 200°C and may preserve
The GRAIL spacecraft measured the gravity field of the Moon at high resolution, allowing determination of the bulk density and porosity of the lunar crust. The analysis found:
1) The bulk density of the lunar highlands crust is 2550 kg/m3, substantially lower than previous estimates due to impact-induced porosity.
2) The average porosity of the crust is 12%, varying regionally from 4-21% and correlated with impact basins.
3) A new global crustal thickness model was constructed satisfying seismic constraints with an average thickness of 34-43 km, indicating the Moon's composition is not highly enriched compared to Earth.
Volatile and organic_composition_of_sedimentary_rocks_in_yellowknife_bay_gale...Sérgio Sacani
This document summarizes the results of experiments analyzing the volatile and organic compositions of sedimentary rock samples from Yellowknife Bay in Gale Crater, Mars. The samples were obtained using the Curiosity rover's drill. Analysis found the samples released water, carbon dioxide, sulfur dioxide, oxygen, and other gases when heated. The water and oxygen releases suggest the presence of hydrated minerals like phyllosilicates and oxychlorine compounds. Small amounts of organic compounds, including chlorinated hydrocarbons, were also detected, though the carbon source is uncertain. The sediments appear to have preserved evidence of past environmental conditions and potential habitability in Yellowknife Bay.
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.
The document summarizes the elemental geochemistry of sedimentary rocks analyzed by the Curiosity rover at Yellowknife Bay, Mars. Key findings include:
1) The rocks have compositions similar to iron-rich basalt and contain elevated levels of iron, chlorine, and calcium sulfate compared to most Martian soils.
2) Mineralogical analysis found phyllosilicates, magnetite, calcium sulfates, and an amorphous component in the mudstones.
3) Geochemical evidence suggests magnetite is likely a diagenetic mineral that formed after deposition rather than a detrital mineral delivered from another source.
4) Ternary diagrams of elemental compositions indicate secondary alteration minerals
Mineralogy of a_mudstone_at_yellowknife_bay_gale_crater_marsSérgio Sacani
The document summarizes the mineralogical analysis of two mudstone samples, John Klein and Cumberland, collected from Yellowknife Bay on Mars by the Curiosity rover. X-ray diffraction analysis found that the samples contain detrital basaltic minerals, calcium sulfates, iron oxides/hydroxides, iron sulfides, amorphous material, and trioctahedral smectites. The smectite in John Klein has a basal spacing of ~10 Å indicating little water interlayer hydration, while Cumberland smectite has a spacing of ~13.2 Å, suggesting partial chloritization or interlayer ions that facilitate water retention. The mudstone minerals are similar to nearby eolian deposits but
Analysis of Surface Materials by Curiosity Mars Rover - Special CollectionCarlos Bella
Curiosity used its instruments to analyze materials along its traverse on Mars, yielding three key results:
1) It found a unique alkaline volcanic rock called "Jake_M" that is compositionally similar to rare mugearite rocks on Earth.
2) It analyzed windblown deposits and found two soil types - a common mafic type similar to global Martian soils, and a locally derived felsic type from broken down bedrock.
3) Chemical analysis of the soils found evidence of hydration in the amorphous soil components, suggesting absorbed water plays a role in Mars' global hydration signal detected from orbiters.
Is ground solid enough to stand on. Authors: Virginia Evans, Ksenia Baranova/...slg1703
The document discusses the composition and structure of Earth's spheres - the lithosphere, atmosphere, hydrosphere, and biosphere. It describes the lithosphere as the solid outer part consisting of the crust and upper mantle. It then discusses the composition of the atmosphere and its layers, as well as the composition and role of the hydrosphere in maintaining life and climate on Earth. It concludes by noting the importance of international cooperation to address pollution threatening the hydrosphere.
This document provides an overview of a module on plate tectonics that includes the following:
1) The module covers topics on evidence of plate tectonics and managing effects of natural phenomena associated with plate tectonics through 4 lessons on the structure of Earth, formation of continents, earthquakes, and volcanoes.
2) Students will complete a pre-assessment on their understanding of the structure of Earth, movement of tectonic plates, earthquakes, and volcanoes from elementary science.
3) The module will help students develop a better understanding of plate tectonics to inform decisions on managing effects of natural phenomena through acquiring scientific knowledge from the lessons and activities.
This document discusses the provenance of quartz arenite sandstones from the early Paleozoic midcontinent region of the USA. The authors present new detrital zircon geochronology data from 15 Cambrian and Ordovician quartz arenite samples. They compare this to existing data from older sedimentary basins in the region, including the Huron basin and midcontinent rift deposits. Mixing models using the older basin zircon populations indicate the early Paleozoic sandstones represent mixtures derived primarily from erosion of these two source areas.
This document provides information about the structure and composition of the Earth. It describes the four main spheres (biosphere, atmosphere, hydrosphere, geosphere). It details the layers of the Earth's interior including the crust, mantle, and core. It explains how the lithosphere is composed of tectonic plates that move and interact at plate boundaries. It also discusses the three main types of rocks: igneous, metamorphic, and sedimentary rocks and how they are formed by volcanic, pressure-related, and sediment-based processes respectively.
The document provides information on various topics in engineering geology including:
1. Definitions of engineering geology, geology, and their importance in civil engineering projects like understanding construction materials, groundwater, and foundations.
2. Branches of geology like physical geology, petrology, structural geology, and their focus on natural earth processes, rock origins and structures.
3. Key geological concepts like weathering, rock excavation methods, faults, folds, strike and dip, and seismic waves from earthquakes.
4. The importance of understanding local geology for planning major engineering works.
- The undergraduate teaching labs at the department have been completely remodeled and updated with new electronic equipment. Prexy's Pasture outside the building has also been remodeled by removing streets and cars for new pedestrian walkways.
- The Third Annual Rocky Mountain Rendezvous and job fair was successful in attracting students from other universities and receiving positive feedback from recruiters about the department's students.
- Advertisements have been posted to replace a paleontologist faculty member and hire for a new sedimentology position in order to rebuild the soft rock program faculty.
- A pillar of the department for many years, Don Blackstone, sadly passed away on May 24th.
The document discusses facts about planet Earth. It describes Earth's three main layers - the crust, mantle, and core. The crust is made up of tectonic plates that are constantly shifting due to convection currents in the mantle. This movement of the plates over millions of years can cause continents to collide, drift apart, or move past each other in the process of continental drift, which is still occurring today.
The ChemCam instrument on the Curiosity rover identified two main soil types on Mars - a fine-grained mafic soil and a coarse-grained felsic soil locally derived. The mafic soil is similar to widespread martian soils and dust, and possesses a ubiquitous hydrogen signature from hydrated amorphous phases. This hydration may account for a significant fraction of hydrogen detected globally on Mars. ChemCam analyses did not reveal water vapor exchange between the soil and atmosphere. The observations provide constraints on the nature and hydration of amorphous phases in the soil.
Earth is composed of four main layers - crust, mantle, outer core, and inner core. The crust is the outermost layer and is made up of either continental or oceanic crust. Below the crust is the mantle, which is divided into lithosphere, asthenosphere, upper mantle, and lower mantle. The outer core is a liquid layer made of nickel and iron that generates Earth's magnetic field. The inner core is made of solid iron deep within Earth. Overall, Earth's composition is approximately 34.6% iron, 29.5% oxygen, and 15.2% silicon.
The document provides information about geology and the structure of the Earth. It discusses the following key points:
1. Geology is the study of the Earth, including its chemical and physical properties, formation processes, and changes from creation to present day.
2. The Earth is composed of several layers including the crust, mantle, outer core, and inner core. The crust and upper mantle make up the lithosphere which is divided into tectonic plates.
3. The formation of the Earth and solar system is explained by several hypotheses including the nebular hypothesis which postulates that the Earth formed from a contracting cloud of gas and dust around the sun.
This document is a note packet for a unit on geologic history from an Earth Science class. It includes vocabulary words and concepts related to relative dating techniques, the geologic time scale, fossil records, evolution of life on Earth, and absolute dating using radioactive isotopes. Key events covered are the formation of Earth and development of its atmosphere, variations and evolution of life forms through geologic time as evidenced by fossils, and methods for correlating and dating rock layers both relatively and absolutely.
The document discusses the geological time scale and major mass extinctions that have occurred throughout history. It describes how time is divided into eons, eras, periods, and epochs. Five major mass extinctions are outlined, including the Ordovician-Silurian, Late Devonian, Permian-Triassic, End Triassic, and Cretaceous-Tertiary extinctions. Each mass extinction significantly reduced marine and land animal populations due to events like asteroid impacts, volcanic eruptions, and climate change.
1) The solar system formed from a nebular cloud of dust and gas approximately 4.6 billion years ago. Early Earth was very different than today, and geological evidence shows the dramatic effects of asteroid impacts on shaping planets.
2) The solar system is located in the outer edge of the Milky Way galaxy, which contains billions of stars. Galaxies make up most of the visible mass of the universe, which has been expanding for 10-20 billion years according to the big bang model.
3) Impact craters provide evidence that asteroids and comets frequently strike planets like Earth, Mars, and Jupiter's moons, with typical impact speeds around 20 km/s producing craters 10-20 times the object
Ancient aqueous environments_at_endeavour_crater_marsSérgio Sacani
The document summarizes findings from the Mars Exploration Rover Opportunity regarding ancient aqueous environments at Endeavour Crater on Mars. CRISM orbital data identified a location with a spectral signature of Fe3+-rich smectite clay minerals. Opportunity investigated this area in detail called the Matijevic formation. It found fine-grained layered rocks containing spherical concretions and was cut by calcium sulfate veins. Composition data suggests the rocks formed from aqueous leaching that altered the rocks to aluminum-rich smectites. This provides evidence for water-rock interactions before and after the impact, under slightly acidic to neutral pH environments that could have been more favorable for prebiotic chemistry.
The surface of Pluto is more geologically diverse and dynamic than had been expected,
but the role of its tenuous atmosphere in shaping the landscape remains unclear. We
describe observations from the New Horizons spacecraft of regularly spaced, linear ridges
whose morphology, distribution, and orientation are consistent with being transverse
dunes. These are located close to mountainous regions and are orthogonal to nearby wind
streaks. We demonstrate that the wavelength of the dunes (~0.4 to 1 kilometer) is best
explained by the deposition of sand-sized (~200 to ~300 micrometer) particles of methane
ice in moderate winds (<10 meters per second). The undisturbed morphology of the dunes,
and relationships with the underlying convective glacial ice, imply that the dunes have
formed in the very recent geological past.
A Tale of 3 Dwarf Planets: Ices and Organics on Sedna, Gonggong, and Quaoar f...Sérgio Sacani
The dwarf planets Sedna, Gonggong, and Quaoar are interesting in being somewhat smaller than
the methane-rich bodies of the Kuiper Belt (Pluto, Eris, Makemake), yet large enough to be
spherical and to have possibly undergone interior melting and differentiation. They also reside
on very different orbits, making them an ideal suite of bodies for untangling effects of size and
orbit on present day surface composition. We observed Sedna, Gonggong, and Quaoar with the
NIRSpec instrument on the James Webb Space Telescope (JWST). All three bodies were
observed in the low-resolution prism mode at wavelengths spanning 0.7 to 5.2 μm. Quaoar was
additionally observed at 10x higher spectral resolution from 0.97 to 3.16 μm using mediumresolution gratings. Sedna’s spectrum shows a large number of absorption features due to ethane
(C2H6), as well as acetylene (C2H2), ethylene (C2H4), H2O, and possibly minor CO2.
Gonggong’s spectrum also shows several, but fewer and weaker, ethane features, along with
stronger and cleaner H2O features and CO2 complexed with other molecules. Quaoar’s prism
spectrum shows even fewer and weaker ethane features, the deepest and cleanest H2O features, a
feature at 3.2 μm possibly due to HCN, and CO2 ice. The higher-resolution medium grating
spectrum of Quaoar reveals several overtone and combination bands of ethane and methane
(CH4). Spectra of all three objects show steep red spectral slopes and strong, broad absorptions
between 2.7 and 3.6 μm indicative of complex organic molecules. The suite of light
hydrocarbons and complex organic molecules are interpreted as the products of irradiation of
methane. The differences in apparent abundances of irradiation products among these three
similarly-sized bodies are likely due to their distinctive orbits, which lead to different timescales
of methane retention and to different charged particle irradiation environments. In all cases,
however, the continued presence of light hydrocarbons implies a resupply of methane to the
2
surface. We suggest that these three bodies have undergone internal melting and geochemical
evolution similar to the larger dwarf planets and distinct from all smaller KBOs. The feature
identification presented in this paper is the first step of analysis, and additional insight into the
relative abundances and mixing states of materials on these surfaces will come from future
spectral modeling of these data.
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.
Volatile and organic_composition_of_sedimentary_rocks_in_yellowknife_bay_gale...Sérgio Sacani
This document summarizes the results of experiments analyzing the volatile and organic compositions of sedimentary rock samples from Yellowknife Bay in Gale Crater, Mars. The samples were obtained using the Curiosity rover's drill. Analysis found the samples released water, carbon dioxide, sulfur dioxide, oxygen, and other gases when heated. The water and oxygen releases suggest the presence of hydrated minerals like phyllosilicates and oxychlorine compounds. Small amounts of organic compounds, including chlorinated hydrocarbons, were also detected, though the carbon source is uncertain. The sediments appear to have preserved evidence of past environmental conditions and potential habitability in Yellowknife Bay.
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.
The document summarizes the elemental geochemistry of sedimentary rocks analyzed by the Curiosity rover at Yellowknife Bay, Mars. Key findings include:
1) The rocks have compositions similar to iron-rich basalt and contain elevated levels of iron, chlorine, and calcium sulfate compared to most Martian soils.
2) Mineralogical analysis found phyllosilicates, magnetite, calcium sulfates, and an amorphous component in the mudstones.
3) Geochemical evidence suggests magnetite is likely a diagenetic mineral that formed after deposition rather than a detrital mineral delivered from another source.
4) Ternary diagrams of elemental compositions indicate secondary alteration minerals
Mineralogy of a_mudstone_at_yellowknife_bay_gale_crater_marsSérgio Sacani
The document summarizes the mineralogical analysis of two mudstone samples, John Klein and Cumberland, collected from Yellowknife Bay on Mars by the Curiosity rover. X-ray diffraction analysis found that the samples contain detrital basaltic minerals, calcium sulfates, iron oxides/hydroxides, iron sulfides, amorphous material, and trioctahedral smectites. The smectite in John Klein has a basal spacing of ~10 Å indicating little water interlayer hydration, while Cumberland smectite has a spacing of ~13.2 Å, suggesting partial chloritization or interlayer ions that facilitate water retention. The mudstone minerals are similar to nearby eolian deposits but
Analysis of Surface Materials by Curiosity Mars Rover - Special CollectionCarlos Bella
Curiosity used its instruments to analyze materials along its traverse on Mars, yielding three key results:
1) It found a unique alkaline volcanic rock called "Jake_M" that is compositionally similar to rare mugearite rocks on Earth.
2) It analyzed windblown deposits and found two soil types - a common mafic type similar to global Martian soils, and a locally derived felsic type from broken down bedrock.
3) Chemical analysis of the soils found evidence of hydration in the amorphous soil components, suggesting absorbed water plays a role in Mars' global hydration signal detected from orbiters.
Is ground solid enough to stand on. Authors: Virginia Evans, Ksenia Baranova/...slg1703
The document discusses the composition and structure of Earth's spheres - the lithosphere, atmosphere, hydrosphere, and biosphere. It describes the lithosphere as the solid outer part consisting of the crust and upper mantle. It then discusses the composition of the atmosphere and its layers, as well as the composition and role of the hydrosphere in maintaining life and climate on Earth. It concludes by noting the importance of international cooperation to address pollution threatening the hydrosphere.
This document provides an overview of a module on plate tectonics that includes the following:
1) The module covers topics on evidence of plate tectonics and managing effects of natural phenomena associated with plate tectonics through 4 lessons on the structure of Earth, formation of continents, earthquakes, and volcanoes.
2) Students will complete a pre-assessment on their understanding of the structure of Earth, movement of tectonic plates, earthquakes, and volcanoes from elementary science.
3) The module will help students develop a better understanding of plate tectonics to inform decisions on managing effects of natural phenomena through acquiring scientific knowledge from the lessons and activities.
This document discusses the provenance of quartz arenite sandstones from the early Paleozoic midcontinent region of the USA. The authors present new detrital zircon geochronology data from 15 Cambrian and Ordovician quartz arenite samples. They compare this to existing data from older sedimentary basins in the region, including the Huron basin and midcontinent rift deposits. Mixing models using the older basin zircon populations indicate the early Paleozoic sandstones represent mixtures derived primarily from erosion of these two source areas.
This document provides information about the structure and composition of the Earth. It describes the four main spheres (biosphere, atmosphere, hydrosphere, geosphere). It details the layers of the Earth's interior including the crust, mantle, and core. It explains how the lithosphere is composed of tectonic plates that move and interact at plate boundaries. It also discusses the three main types of rocks: igneous, metamorphic, and sedimentary rocks and how they are formed by volcanic, pressure-related, and sediment-based processes respectively.
The document provides information on various topics in engineering geology including:
1. Definitions of engineering geology, geology, and their importance in civil engineering projects like understanding construction materials, groundwater, and foundations.
2. Branches of geology like physical geology, petrology, structural geology, and their focus on natural earth processes, rock origins and structures.
3. Key geological concepts like weathering, rock excavation methods, faults, folds, strike and dip, and seismic waves from earthquakes.
4. The importance of understanding local geology for planning major engineering works.
- The undergraduate teaching labs at the department have been completely remodeled and updated with new electronic equipment. Prexy's Pasture outside the building has also been remodeled by removing streets and cars for new pedestrian walkways.
- The Third Annual Rocky Mountain Rendezvous and job fair was successful in attracting students from other universities and receiving positive feedback from recruiters about the department's students.
- Advertisements have been posted to replace a paleontologist faculty member and hire for a new sedimentology position in order to rebuild the soft rock program faculty.
- A pillar of the department for many years, Don Blackstone, sadly passed away on May 24th.
The document discusses facts about planet Earth. It describes Earth's three main layers - the crust, mantle, and core. The crust is made up of tectonic plates that are constantly shifting due to convection currents in the mantle. This movement of the plates over millions of years can cause continents to collide, drift apart, or move past each other in the process of continental drift, which is still occurring today.
The ChemCam instrument on the Curiosity rover identified two main soil types on Mars - a fine-grained mafic soil and a coarse-grained felsic soil locally derived. The mafic soil is similar to widespread martian soils and dust, and possesses a ubiquitous hydrogen signature from hydrated amorphous phases. This hydration may account for a significant fraction of hydrogen detected globally on Mars. ChemCam analyses did not reveal water vapor exchange between the soil and atmosphere. The observations provide constraints on the nature and hydration of amorphous phases in the soil.
Earth is composed of four main layers - crust, mantle, outer core, and inner core. The crust is the outermost layer and is made up of either continental or oceanic crust. Below the crust is the mantle, which is divided into lithosphere, asthenosphere, upper mantle, and lower mantle. The outer core is a liquid layer made of nickel and iron that generates Earth's magnetic field. The inner core is made of solid iron deep within Earth. Overall, Earth's composition is approximately 34.6% iron, 29.5% oxygen, and 15.2% silicon.
The document provides information about geology and the structure of the Earth. It discusses the following key points:
1. Geology is the study of the Earth, including its chemical and physical properties, formation processes, and changes from creation to present day.
2. The Earth is composed of several layers including the crust, mantle, outer core, and inner core. The crust and upper mantle make up the lithosphere which is divided into tectonic plates.
3. The formation of the Earth and solar system is explained by several hypotheses including the nebular hypothesis which postulates that the Earth formed from a contracting cloud of gas and dust around the sun.
This document is a note packet for a unit on geologic history from an Earth Science class. It includes vocabulary words and concepts related to relative dating techniques, the geologic time scale, fossil records, evolution of life on Earth, and absolute dating using radioactive isotopes. Key events covered are the formation of Earth and development of its atmosphere, variations and evolution of life forms through geologic time as evidenced by fossils, and methods for correlating and dating rock layers both relatively and absolutely.
The document discusses the geological time scale and major mass extinctions that have occurred throughout history. It describes how time is divided into eons, eras, periods, and epochs. Five major mass extinctions are outlined, including the Ordovician-Silurian, Late Devonian, Permian-Triassic, End Triassic, and Cretaceous-Tertiary extinctions. Each mass extinction significantly reduced marine and land animal populations due to events like asteroid impacts, volcanic eruptions, and climate change.
1) The solar system formed from a nebular cloud of dust and gas approximately 4.6 billion years ago. Early Earth was very different than today, and geological evidence shows the dramatic effects of asteroid impacts on shaping planets.
2) The solar system is located in the outer edge of the Milky Way galaxy, which contains billions of stars. Galaxies make up most of the visible mass of the universe, which has been expanding for 10-20 billion years according to the big bang model.
3) Impact craters provide evidence that asteroids and comets frequently strike planets like Earth, Mars, and Jupiter's moons, with typical impact speeds around 20 km/s producing craters 10-20 times the object
Ancient aqueous environments_at_endeavour_crater_marsSérgio Sacani
The document summarizes findings from the Mars Exploration Rover Opportunity regarding ancient aqueous environments at Endeavour Crater on Mars. CRISM orbital data identified a location with a spectral signature of Fe3+-rich smectite clay minerals. Opportunity investigated this area in detail called the Matijevic formation. It found fine-grained layered rocks containing spherical concretions and was cut by calcium sulfate veins. Composition data suggests the rocks formed from aqueous leaching that altered the rocks to aluminum-rich smectites. This provides evidence for water-rock interactions before and after the impact, under slightly acidic to neutral pH environments that could have been more favorable for prebiotic chemistry.
The surface of Pluto is more geologically diverse and dynamic than had been expected,
but the role of its tenuous atmosphere in shaping the landscape remains unclear. We
describe observations from the New Horizons spacecraft of regularly spaced, linear ridges
whose morphology, distribution, and orientation are consistent with being transverse
dunes. These are located close to mountainous regions and are orthogonal to nearby wind
streaks. We demonstrate that the wavelength of the dunes (~0.4 to 1 kilometer) is best
explained by the deposition of sand-sized (~200 to ~300 micrometer) particles of methane
ice in moderate winds (<10 meters per second). The undisturbed morphology of the dunes,
and relationships with the underlying convective glacial ice, imply that the dunes have
formed in the very recent geological past.
A Tale of 3 Dwarf Planets: Ices and Organics on Sedna, Gonggong, and Quaoar f...Sérgio Sacani
The dwarf planets Sedna, Gonggong, and Quaoar are interesting in being somewhat smaller than
the methane-rich bodies of the Kuiper Belt (Pluto, Eris, Makemake), yet large enough to be
spherical and to have possibly undergone interior melting and differentiation. They also reside
on very different orbits, making them an ideal suite of bodies for untangling effects of size and
orbit on present day surface composition. We observed Sedna, Gonggong, and Quaoar with the
NIRSpec instrument on the James Webb Space Telescope (JWST). All three bodies were
observed in the low-resolution prism mode at wavelengths spanning 0.7 to 5.2 μm. Quaoar was
additionally observed at 10x higher spectral resolution from 0.97 to 3.16 μm using mediumresolution gratings. Sedna’s spectrum shows a large number of absorption features due to ethane
(C2H6), as well as acetylene (C2H2), ethylene (C2H4), H2O, and possibly minor CO2.
Gonggong’s spectrum also shows several, but fewer and weaker, ethane features, along with
stronger and cleaner H2O features and CO2 complexed with other molecules. Quaoar’s prism
spectrum shows even fewer and weaker ethane features, the deepest and cleanest H2O features, a
feature at 3.2 μm possibly due to HCN, and CO2 ice. The higher-resolution medium grating
spectrum of Quaoar reveals several overtone and combination bands of ethane and methane
(CH4). Spectra of all three objects show steep red spectral slopes and strong, broad absorptions
between 2.7 and 3.6 μm indicative of complex organic molecules. The suite of light
hydrocarbons and complex organic molecules are interpreted as the products of irradiation of
methane. The differences in apparent abundances of irradiation products among these three
similarly-sized bodies are likely due to their distinctive orbits, which lead to different timescales
of methane retention and to different charged particle irradiation environments. In all cases,
however, the continued presence of light hydrocarbons implies a resupply of methane to the
2
surface. We suggest that these three bodies have undergone internal melting and geochemical
evolution similar to the larger dwarf planets and distinct from all smaller KBOs. The feature
identification presented in this paper is the first step of analysis, and additional insight into the
relative abundances and mixing states of materials on these surfaces will come from future
spectral modeling of these data.
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.
The dynamic geophysical environment of (101955) Bennu based on OSIRIS-REx mea...Sérgio Sacani
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.
Modern water at low latitudes on Mars: Potential evidence from dune surfacesSérgio Sacani
Landforms on the Martian surface are critical to understanding the nature of surface processes in the recent
past. However, modern hydroclimatic conditions on Mars remain enigmatic, as explanations for the formation
of observed landforms are ambiguous. We report crusts, cracks, aggregates, and bright polygonal ridges on the
surfaces of hydrated salt-rich dunes of southern Utopia Planitia (~25°N) from in situ exploration by the Zhurong
rover. These surface features were inferred to form after 1.4 to 0.4 million years ago. Wind and CO2 frost processes can be ruled out as potential mechanisms. Instead, involvement of saline water from thawed frost/snow is
the most likely cause. This discovery sheds light on more humid conditions of the modern Martian climate and
provides critical clues to future exploration missions searching for signs of extant life, particularly at low latitudes with comparatively warmer, more amenable surface temperatures.
The document contains a 10 question quiz about the electromagnetic spectrum and related topics like radiation, global warming, and the greenhouse effect. The questions cover topics such as the different types of radiation, how they are used and their effects, how food is cooked in microwaves, what gases cause global warming, and what the greenhouse effect has on Earth.
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.
The Moonraker mission is a proposed ESA M-class mission to study Enceladus through multiple flybys. Its goals are to 1) assess the habitability of Enceladus' subsurface ocean by analyzing plume composition, 2) understand communication between the ocean and surface, and 3) determine Enceladus' formation conditions. It would carry advanced instruments to precisely measure species, isotopes, and physical properties in the plume and on the surface. The mission aims to characterize Enceladus' potential as an abiotic and biological oasis.
Exploring Martian Magnetic Fields with a HelicopterSérgio Sacani
The era of helicopter-based surveys on Mars has already begun, creating opportunities for future aerial science
investigations with a range of instruments. We argue that magnetometer-based studies can make use of aerial
technology to answer some of the key questions regarding early Mars evolution. As such, we discuss mission
concepts for a helicopter equipped with a magnetometer on Mars, measurements it would provide, and survey
designs that could be implemented. For a range of scenarios, we build magnetization models and test how well
structures can be resolved using a range of different inversion approaches. With this work, we provide modeling
ground work and recommendations to plan the future of aerial Mars exploration.
The operational environment and rotational acceleration of asteroid (101955) ...Sérgio Sacani
During its approach to asteroid (101955) Bennu, NASA’s Origins, Spectral Interpretation,
Resource Identification, and Security-Regolith Explorer (OSIRIS-REx) spacecraft surveyed
Bennu’s immediate environment, photometric properties, and rotation state. Discovery of
a dusty environment, a natural satellite, or unexpected asteroid characteristics would have
had consequences for the mission’s safety and observation strategy. Here we show that
spacecraft observations during this period were highly sensitive to satellites (sub-meter
scale) but reveal none, although later navigational images indicate that further investigation is
needed. We constrain average dust production in September 2018 from Bennu’s surface
to an upper limit of 150 g s–1 averaged over 34 min. Bennu’s disk-integrated photometric
phase function validates measurements from the pre-encounter astronomical campaign.
We demonstrate that Bennu’s rotation rate is accelerating continuously at 3.63 ± 0.52 × 10–6
degrees day–2, likely due to the Yarkovsky–O’Keefe–Radzievskii–Paddack (YORP) effect, with
evolutionary implications.
Molecular gas clumps_from_the_destruction_of_icy_bodies_in_beta_pictoris_debr...Sérgio Sacani
1) ALMA observations detected carbon monoxide gas orbiting in a debris disk around the young star Beta Pictoris, with a total mass equivalent to 0.0023 times the mass of Earth's Moon.
2) The gas is distributed asymmetrically, with 30% located in a single clump 85 AU from the star. This gas clump is aligned with the orbit of an inner planet in the system.
3) The gas must be continuously replenished, likely from the destruction of icy planetesimals and comets through collisions within the debris disk. The collisions may be enhanced in the gas clump due to resonances with an unseen giant planet or from remnants of a large collision between
Molecular Gas Clumps from the Destruction of Icy Bodies in the β Pictoris Deb...GOASA
1) ALMA observations detected carbon monoxide gas orbiting in a debris disk around the young star Beta Pictoris, with a total mass equivalent to 0.0023 times the mass of Earth's Moon.
2) The gas is distributed asymmetrically, with 30% located in a single clump 85 AU from the star. This gas clump is aligned with the orbit of an inner planet in the system.
3) The gas must be continuously replenished, likely from the destruction of icy planetesimals and comets through collisions within the debris disk. The collisions may be enhanced in the gas clump due to resonances with an unseen giant planet or the remnants of a large collision between
This document analyzes structural mapping data of the central uplift region of Martin Crater on Mars to test predictions of acoustic fluidization models of central peak formation. The mapping shows the megablocks in the uplift are intricately interconnected with correlated bedding planes across boundaries, forming large folds accommodated by fracturing with little internal strain. Block separation measurements are far less than required for acoustic fluidization. The data are inconsistent with the block model of fluidization and suggest fluidization played a minor role, while not proposing an alternative formation mechanism.
The document summarizes key information about the geology of Venus. It states that Venus' surface is only about 500 million years old, as evidenced by impact craters, yet erosion rates are very low. Notable surface features include pancake-shaped volcanoes, coronae, and tectonic ridges and cracks. Venus has a slow 243-day rotation period that results in low wind speeds and erosion. Its atmosphere is extremely hot and dense.
An ESA Study For The Search For Life On MarsFaith Brown
This document proposes a hypothetical strategy to search for life on Mars using robotic missions. It discusses the following key points:
1. Mars and early Earth had similar environments that could have supported the development of life, so life may have arisen on Mars as well in a primitive prokaryotic form.
2. A robotic mission should carefully select landing sites with good exobiological potential to find chemical or morphological biosignatures. Samples would be collected and analyzed using integrated instruments on a lander and rover.
3. The goal is to obtain environmental data, look for microscopic evidence of life, analyze biogeochemistry, and identify potential niches for extant life to increase the chances of detecting past or present
The harps n-rocky_planet_search_hd219134b_transiting_rocky_planetSérgio Sacani
Usando o espectrógrafo HARPS-N acoplado ao Telescopio Nazionale Galileo no Observatório de Roque de Los Muchachos, nas Ilhas Canárias, os astrônomos descobriram três exoplanetas, classificados como Super-Terras e um gigante gasoso orbitando uma estrela próxima, chamada de HD 219134.
A HD 219134, também conhecida como HR 8832 é uma estrela do tipo anã-K de quinta magnitude, localizada a aproximadamente 21 anos-luz de distância da Terra, na constelação de Cassiopeia.
A estrela é levemente mais fria e menos massiva que o nosso sol. Ela é tão brilhante que pode ser observada a olho nu.
O sistema planetário HD 219134, abriga um planeta gigante gasoso externo e três planetas internos classificados como super-Terras, um dos quais transita em frente à estrela.
The Expansion of the X-Ray Nebula Around η CarSérgio Sacani
1. The author analyzes over 20 years of Chandra X-ray images to measure for the first time the expansion of the X-ray nebula around η Carinae.
2. A combined Chandra image reveals a faint, nearly uniform elliptical shell surrounding the X-ray bright ring, with a similar orientation and shape as the Homunculus nebula but about 3 times larger.
3. The author measures proper motions of brighter regions associated with the X-ray emitting ring, such as the S-ridge and W-arc. Motions are consistent with optical studies of ejecta from the 1840s Great Eruption.
This document reports on high-resolution images from the MESSENGER spacecraft that reveal unusual landforms on Mercury characterized by irregular, shallow depressions known as hollows. The hollows range in size and are commonly found in clusters associated with high-reflectance materials within impact craters. The most likely formation mechanisms involve recent loss of volatile materials through processes like sublimation or pyroclastic volcanism. These features suggest Mercury's interior contains more volatile materials than predicted, challenging models of the planet's formation.
The document summarizes findings from studying asteroid 4 Vesta using data from NASA's Dawn spacecraft. It finds that Vesta has experienced a violent collisional history, with large impacts creating steep slopes and resurfacing much of the surface. While no unambiguous volcanic deposits were found, some dark material in impact craters may be from excavated subsurface volcanic features. Smooth ponds found on Vesta are also seen on asteroid Eros and are thought to form from impact ejecta collecting in depressions.
Spirals and clumps in V960 Mon: signs of planet formation via gravitational i...Sérgio Sacani
The formation of giant planets has traditionally been divided into two pathways: core accretion and gravitational instability. However, in recent years, gravitational instability has become less favored, primarily due
to the scarcity of observations of fragmented protoplanetary disks around young stars and low occurrence rate
of massive planets on very wide orbits. In this study, we present a SPHERE/IRDIS polarized light observation
of the young outbursting object V960 Mon. The image reveals a vast structure of intricately shaped scattered
light with several spiral arms. This finding motivated a re-analysis of archival ALMA 1.3 mm data acquired
just two years after the onset of the outburst of V960 Mon. In these data, we discover several clumps of continuum emission aligned along a spiral arm that coincides with the scattered light structure. We interpret the
localized emission as fragments formed from a spiral arm under gravitational collapse. Estimating the mass of
solids within these clumps to be of several Earth masses, we suggest this observation to be the first evidence of
gravitational instability occurring on planetary scales. This study discusses the significance of this finding for
planet formation and its potential connection with the outbursting state of V960 Mon.
Ages and stratigraphy of lunar mare basalts a synthesisSérgio Sacani
This document summarizes ages and stratigraphy of lunar mare basalts based on a synthesis of crater counting efforts over more than 10 years. The key points are:
1) Lunar volcanism was active for almost 3 billion years, starting around 3.9-4 billion years ago and ceasing around 1.2 billion years ago.
2) Most basalts erupted during the late Imbrian period around 3.6-3.8 billion years ago.
3) Significantly fewer basalts were emplaced during the Eratosthenian period.
4) Basalts of possible Copernican age have only been found in limited areas of Oceanus Procellarum.
Similar to Craters, boulders and regolith of (101955) Bennu indicative of an old and dynamic surface (20)
SDSS1335+0728: The awakening of a ∼ 106M⊙ black hole⋆Sérgio Sacani
Context. The early-type galaxy SDSS J133519.91+072807.4 (hereafter SDSS1335+0728), which had exhibited no prior optical variations during the preceding two decades, began showing significant nuclear variability in the Zwicky Transient Facility (ZTF) alert stream from December 2019 (as ZTF19acnskyy). This variability behaviour, coupled with the host-galaxy properties, suggests that SDSS1335+0728 hosts a ∼ 106M⊙ black hole (BH) that is currently in the process of ‘turning on’. Aims. We present a multi-wavelength photometric analysis and spectroscopic follow-up performed with the aim of better understanding the origin of the nuclear variations detected in SDSS1335+0728. Methods. We used archival photometry (from WISE, 2MASS, SDSS, GALEX, eROSITA) and spectroscopic data (from SDSS and LAMOST) to study the state of SDSS1335+0728 prior to December 2019, and new observations from Swift, SOAR/Goodman, VLT/X-shooter, and Keck/LRIS taken after its turn-on to characterise its current state. We analysed the variability of SDSS1335+0728 in the X-ray/UV/optical/mid-infrared range, modelled its spectral energy distribution prior to and after December 2019, and studied the evolution of its UV/optical spectra. Results. From our multi-wavelength photometric analysis, we find that: (a) since 2021, the UV flux (from Swift/UVOT observations) is four times brighter than the flux reported by GALEX in 2004; (b) since June 2022, the mid-infrared flux has risen more than two times, and the W1−W2 WISE colour has become redder; and (c) since February 2024, the source has begun showing X-ray emission. From our spectroscopic follow-up, we see that (i) the narrow emission line ratios are now consistent with a more energetic ionising continuum; (ii) broad emission lines are not detected; and (iii) the [OIII] line increased its flux ∼ 3.6 years after the first ZTF alert, which implies a relatively compact narrow-line-emitting region. Conclusions. We conclude that the variations observed in SDSS1335+0728 could be either explained by a ∼ 106M⊙ AGN that is just turning on or by an exotic tidal disruption event (TDE). If the former is true, SDSS1335+0728 is one of the strongest cases of an AGNobserved in the process of activating. If the latter were found to be the case, it would correspond to the longest and faintest TDE ever observed (or another class of still unknown nuclear transient). Future observations of SDSS1335+0728 are crucial to further understand its behaviour. Key words. galaxies: active– accretion, accretion discs– galaxies: individual: SDSS J133519.91+072807.4
Discovery of An Apparent Red, High-Velocity Type Ia Supernova at 𝐳 = 2.9 wi...Sérgio Sacani
We present the JWST discovery of SN 2023adsy, a transient object located in a host galaxy JADES-GS
+
53.13485
−
27.82088
with a host spectroscopic redshift of
2.903
±
0.007
. The transient was identified in deep James Webb Space Telescope (JWST)/NIRCam imaging from the JWST Advanced Deep Extragalactic Survey (JADES) program. Photometric and spectroscopic followup with NIRCam and NIRSpec, respectively, confirm the redshift and yield UV-NIR light-curve, NIR color, and spectroscopic information all consistent with a Type Ia classification. Despite its classification as a likely SN Ia, SN 2023adsy is both fairly red (
�
(
�
−
�
)
∼
0.9
) despite a host galaxy with low-extinction and has a high Ca II velocity (
19
,
000
±
2
,
000
km/s) compared to the general population of SNe Ia. While these characteristics are consistent with some Ca-rich SNe Ia, particularly SN 2016hnk, SN 2023adsy is intrinsically brighter than the low-
�
Ca-rich population. Although such an object is too red for any low-
�
cosmological sample, we apply a fiducial standardization approach to SN 2023adsy and find that the SN 2023adsy luminosity distance measurement is in excellent agreement (
≲
1
�
) with
Λ
CDM. Therefore unlike low-
�
Ca-rich SNe Ia, SN 2023adsy is standardizable and gives no indication that SN Ia standardized luminosities change significantly with redshift. A larger sample of distant SNe Ia is required to determine if SN Ia population characteristics at high-
�
truly diverge from their low-
�
counterparts, and to confirm that standardized luminosities nevertheless remain constant with redshift.
Evidence of Jet Activity from the Secondary Black Hole in the OJ 287 Binary S...Sérgio Sacani
Wereport the study of a huge optical intraday flare on 2021 November 12 at 2 a.m. UT in the blazar OJ287. In the binary black hole model, it is associated with an impact of the secondary black hole on the accretion disk of the primary. Our multifrequency observing campaign was set up to search for such a signature of the impact based on a prediction made 8 yr earlier. The first I-band results of the flare have already been reported by Kishore et al. (2024). Here we combine these data with our monitoring in the R-band. There is a big change in the R–I spectral index by 1.0 ±0.1 between the normal background and the flare, suggesting a new component of radiation. The polarization variation during the rise of the flare suggests the same. The limits on the source size place it most reasonably in the jet of the secondary BH. We then ask why we have not seen this phenomenon before. We show that OJ287 was never before observed with sufficient sensitivity on the night when the flare should have happened according to the binary model. We also study the probability that this flare is just an oversized example of intraday variability using the Krakow data set of intense monitoring between 2015 and 2023. We find that the occurrence of a flare of this size and rapidity is unlikely. In machine-readable Tables 1 and 2, we give the full orbit-linked historical light curve of OJ287 as well as the dense monitoring sample of Krakow.
Candidate young stellar objects in the S-cluster: Kinematic analysis of a sub...Sérgio Sacani
Context. The observation of several L-band emission sources in the S cluster has led to a rich discussion of their nature. However, a definitive answer to the classification of the dusty objects requires an explanation for the detection of compact Doppler-shifted Brγ emission. The ionized hydrogen in combination with the observation of mid-infrared L-band continuum emission suggests that most of these sources are embedded in a dusty envelope. These embedded sources are part of the S-cluster, and their relationship to the S-stars is still under debate. To date, the question of the origin of these two populations has been vague, although all explanations favor migration processes for the individual cluster members. Aims. This work revisits the S-cluster and its dusty members orbiting the supermassive black hole SgrA* on bound Keplerian orbits from a kinematic perspective. The aim is to explore the Keplerian parameters for patterns that might imply a nonrandom distribution of the sample. Additionally, various analytical aspects are considered to address the nature of the dusty sources. Methods. Based on the photometric analysis, we estimated the individual H−K and K−L colors for the source sample and compared the results to known cluster members. The classification revealed a noticeable contrast between the S-stars and the dusty sources. To fit the flux-density distribution, we utilized the radiative transfer code HYPERION and implemented a young stellar object Class I model. We obtained the position angle from the Keplerian fit results; additionally, we analyzed the distribution of the inclinations and the longitudes of the ascending node. Results. The colors of the dusty sources suggest a stellar nature consistent with the spectral energy distribution in the near and midinfrared domains. Furthermore, the evaporation timescales of dusty and gaseous clumps in the vicinity of SgrA* are much shorter ( 2yr) than the epochs covered by the observations (≈15yr). In addition to the strong evidence for the stellar classification of the D-sources, we also find a clear disk-like pattern following the arrangements of S-stars proposed in the literature. Furthermore, we find a global intrinsic inclination for all dusty sources of 60 ± 20◦, implying a common formation process. Conclusions. The pattern of the dusty sources manifested in the distribution of the position angles, inclinations, and longitudes of the ascending node strongly suggests two different scenarios: the main-sequence stars and the dusty stellar S-cluster sources share a common formation history or migrated with a similar formation channel in the vicinity of SgrA*. Alternatively, the gravitational influence of SgrA* in combination with a massive perturber, such as a putative intermediate mass black hole in the IRS 13 cluster, forces the dusty objects and S-stars to follow a particular orbital arrangement. Key words. stars: black holes– stars: formation– Galaxy: center– galaxies: star formation
JAMES WEBB STUDY THE MASSIVE BLACK HOLE SEEDSSérgio Sacani
The pathway(s) to seeding the massive black holes (MBHs) that exist at the heart of galaxies in the present and distant Universe remains an unsolved problem. Here we categorise, describe and quantitatively discuss the formation pathways of both light and heavy seeds. We emphasise that the most recent computational models suggest that rather than a bimodal-like mass spectrum between light and heavy seeds with light at one end and heavy at the other that instead a continuum exists. Light seeds being more ubiquitous and the heavier seeds becoming less and less abundant due the rarer environmental conditions required for their formation. We therefore examine the different mechanisms that give rise to different seed mass spectrums. We show how and why the mechanisms that produce the heaviest seeds are also among the rarest events in the Universe and are hence extremely unlikely to be the seeds for the vast majority of the MBH population. We quantify, within the limits of the current large uncertainties in the seeding processes, the expected number densities of the seed mass spectrum. We argue that light seeds must be at least 103 to 105 times more numerous than heavy seeds to explain the MBH population as a whole. Based on our current understanding of the seed population this makes heavy seeds (Mseed > 103 M⊙) a significantly more likely pathway given that heavy seeds have an abundance pattern than is close to and likely in excess of 10−4 compared to light seeds. Finally, we examine the current state-of-the-art in numerical calculations and recent observations and plot a path forward for near-future advances in both domains.
Anti-Universe And Emergent Gravity and the Dark UniverseSérgio Sacani
Recent theoretical progress indicates that spacetime and gravity emerge together from the entanglement structure of an underlying microscopic theory. These ideas are best understood in Anti-de Sitter space, where they rely on the area law for entanglement entropy. The extension to de Sitter space requires taking into account the entropy and temperature associated with the cosmological horizon. Using insights from string theory, black hole physics and quantum information theory we argue that the positive dark energy leads to a thermal volume law contribution to the entropy that overtakes the area law precisely at the cosmological horizon. Due to the competition between area and volume law entanglement the microscopic de Sitter states do not thermalise at sub-Hubble scales: they exhibit memory effects in the form of an entropy displacement caused by matter. The emergent laws of gravity contain an additional ‘dark’ gravitational force describing the ‘elastic’ response due to the entropy displacement. We derive an estimate of the strength of this extra force in terms of the baryonic mass, Newton’s constant and the Hubble acceleration scale a0 = cH0, and provide evidence for the fact that this additional ‘dark gravity force’ explains the observed phenomena in galaxies and clusters currently attributed to dark matter.
The binding of cosmological structures by massless topological defectsSérgio Sacani
Assuming spherical symmetry and weak field, it is shown that if one solves the Poisson equation or the Einstein field
equations sourced by a topological defect, i.e. a singularity of a very specific form, the result is a localized gravitational
field capable of driving flat rotation (i.e. Keplerian circular orbits at a constant speed for all radii) of test masses on a thin
spherical shell without any underlying mass. Moreover, a large-scale structure which exploits this solution by assembling
concentrically a number of such topological defects can establish a flat stellar or galactic rotation curve, and can also deflect
light in the same manner as an equipotential (isothermal) sphere. Thus, the need for dark matter or modified gravity theory is
mitigated, at least in part.
EWOCS-I: The catalog of X-ray sources in Westerlund 1 from the Extended Weste...Sérgio Sacani
Context. With a mass exceeding several 104 M⊙ and a rich and dense population of massive stars, supermassive young star clusters
represent the most massive star-forming environment that is dominated by the feedback from massive stars and gravitational interactions
among stars.
Aims. In this paper we present the Extended Westerlund 1 and 2 Open Clusters Survey (EWOCS) project, which aims to investigate
the influence of the starburst environment on the formation of stars and planets, and on the evolution of both low and high mass stars.
The primary targets of this project are Westerlund 1 and 2, the closest supermassive star clusters to the Sun.
Methods. The project is based primarily on recent observations conducted with the Chandra and JWST observatories. Specifically,
the Chandra survey of Westerlund 1 consists of 36 new ACIS-I observations, nearly co-pointed, for a total exposure time of 1 Msec.
Additionally, we included 8 archival Chandra/ACIS-S observations. This paper presents the resulting catalog of X-ray sources within
and around Westerlund 1. Sources were detected by combining various existing methods, and photon extraction and source validation
were carried out using the ACIS-Extract software.
Results. The EWOCS X-ray catalog comprises 5963 validated sources out of the 9420 initially provided to ACIS-Extract, reaching a
photon flux threshold of approximately 2 × 10−8 photons cm−2
s
−1
. The X-ray sources exhibit a highly concentrated spatial distribution,
with 1075 sources located within the central 1 arcmin. We have successfully detected X-ray emissions from 126 out of the 166 known
massive stars of the cluster, and we have collected over 71 000 photons from the magnetar CXO J164710.20-455217.
The debris of the ‘last major merger’ is dynamically youngSérgio Sacani
The Milky Way’s (MW) inner stellar halo contains an [Fe/H]-rich component with highly eccentric orbits, often referred to as the
‘last major merger.’ Hypotheses for the origin of this component include Gaia-Sausage/Enceladus (GSE), where the progenitor
collided with the MW proto-disc 8–11 Gyr ago, and the Virgo Radial Merger (VRM), where the progenitor collided with the
MW disc within the last 3 Gyr. These two scenarios make different predictions about observable structure in local phase space,
because the morphology of debris depends on how long it has had to phase mix. The recently identified phase-space folds in Gaia
DR3 have positive caustic velocities, making them fundamentally different than the phase-mixed chevrons found in simulations
at late times. Roughly 20 per cent of the stars in the prograde local stellar halo are associated with the observed caustics. Based
on a simple phase-mixing model, the observed number of caustics are consistent with a merger that occurred 1–2 Gyr ago.
We also compare the observed phase-space distribution to FIRE-2 Latte simulations of GSE-like mergers, using a quantitative
measurement of phase mixing (2D causticality). The observed local phase-space distribution best matches the simulated data
1–2 Gyr after collision, and certainly not later than 3 Gyr. This is further evidence that the progenitor of the ‘last major merger’
did not collide with the MW proto-disc at early times, as is thought for the GSE, but instead collided with the MW disc within
the last few Gyr, consistent with the body of work surrounding the VRM.
Observation of Io’s Resurfacing via Plume Deposition Using Ground-based Adapt...Sérgio Sacani
Since volcanic activity was first discovered on Io from Voyager images in 1979, changes
on Io’s surface have been monitored from both spacecraft and ground-based telescopes.
Here, we present the highest spatial resolution images of Io ever obtained from a groundbased telescope. These images, acquired by the SHARK-VIS instrument on the Large
Binocular Telescope, show evidence of a major resurfacing event on Io’s trailing hemisphere. When compared to the most recent spacecraft images, the SHARK-VIS images
show that a plume deposit from a powerful eruption at Pillan Patera has covered part
of the long-lived Pele plume deposit. Although this type of resurfacing event may be common on Io, few have been detected due to the rarity of spacecraft visits and the previously low spatial resolution available from Earth-based telescopes. The SHARK-VIS instrument ushers in a new era of high resolution imaging of Io’s surface using adaptive
optics at visible wavelengths.
Earliest Galaxies in the JADES Origins Field: Luminosity Function and Cosmic ...Sérgio Sacani
We characterize the earliest galaxy population in the JADES Origins Field (JOF), the deepest
imaging field observed with JWST. We make use of the ancillary Hubble optical images (5 filters
spanning 0.4−0.9µm) and novel JWST images with 14 filters spanning 0.8−5µm, including 7 mediumband filters, and reaching total exposure times of up to 46 hours per filter. We combine all our data
at > 2.3µm to construct an ultradeep image, reaching as deep as ≈ 31.4 AB mag in the stack and
30.3-31.0 AB mag (5σ, r = 0.1” circular aperture) in individual filters. We measure photometric
redshifts and use robust selection criteria to identify a sample of eight galaxy candidates at redshifts
z = 11.5 − 15. These objects show compact half-light radii of R1/2 ∼ 50 − 200pc, stellar masses of
M⋆ ∼ 107−108M⊙, and star-formation rates of SFR ∼ 0.1−1 M⊙ yr−1
. Our search finds no candidates
at 15 < z < 20, placing upper limits at these redshifts. We develop a forward modeling approach to
infer the properties of the evolving luminosity function without binning in redshift or luminosity that
marginalizes over the photometric redshift uncertainty of our candidate galaxies and incorporates the
impact of non-detections. We find a z = 12 luminosity function in good agreement with prior results,
and that the luminosity function normalization and UV luminosity density decline by a factor of ∼ 2.5
from z = 12 to z = 14. We discuss the possible implications of our results in the context of theoretical
models for evolution of the dark matter halo mass function.
THE IMPORTANCE OF MARTIAN ATMOSPHERE SAMPLE RETURN.Sérgio Sacani
The return of a sample of near-surface atmosphere from Mars would facilitate answers to several first-order science questions surrounding the formation and evolution of the planet. One of the important aspects of terrestrial planet formation in general is the role that primary atmospheres played in influencing the chemistry and structure of the planets and their antecedents. Studies of the martian atmosphere can be used to investigate the role of a primary atmosphere in its history. Atmosphere samples would also inform our understanding of the near-surface chemistry of the planet, and ultimately the prospects for life. High-precision isotopic analyses of constituent gases are needed to address these questions, requiring that the analyses are made on returned samples rather than in situ.
Multi-source connectivity as the driver of solar wind variability in the heli...Sérgio Sacani
The ambient solar wind that flls the heliosphere originates from multiple
sources in the solar corona and is highly structured. It is often described
as high-speed, relatively homogeneous, plasma streams from coronal
holes and slow-speed, highly variable, streams whose source regions are
under debate. A key goal of ESA/NASA’s Solar Orbiter mission is to identify
solar wind sources and understand what drives the complexity seen in the
heliosphere. By combining magnetic feld modelling and spectroscopic
techniques with high-resolution observations and measurements, we show
that the solar wind variability detected in situ by Solar Orbiter in March
2022 is driven by spatio-temporal changes in the magnetic connectivity to
multiple sources in the solar atmosphere. The magnetic feld footpoints
connected to the spacecraft moved from the boundaries of a coronal hole
to one active region (12961) and then across to another region (12957). This
is refected in the in situ measurements, which show the transition from fast
to highly Alfvénic then to slow solar wind that is disrupted by the arrival of
a coronal mass ejection. Our results describe solar wind variability at 0.5 au
but are applicable to near-Earth observatories.
Gliese 12 b: A Temperate Earth-sized Planet at 12 pc Ideal for Atmospheric Tr...Sérgio Sacani
Recent discoveries of Earth-sized planets transiting nearby M dwarfs have made it possible to characterize the
atmospheres of terrestrial planets via follow-up spectroscopic observations. However, the number of such planets
receiving low insolation is still small, limiting our ability to understand the diversity of the atmospheric
composition and climates of temperate terrestrial planets. We report the discovery of an Earth-sized planet
transiting the nearby (12 pc) inactive M3.0 dwarf Gliese 12 (TOI-6251) with an orbital period (Porb) of 12.76 days.
The planet, Gliese 12 b, was initially identified as a candidate with an ambiguous Porb from TESS data. We
confirmed the transit signal and Porb using ground-based photometry with MuSCAT2 and MuSCAT3, and
validated the planetary nature of the signal using high-resolution images from Gemini/NIRI and Keck/NIRC2 as
well as radial velocity (RV) measurements from the InfraRed Doppler instrument on the Subaru 8.2 m telescope
and from CARMENES on the CAHA 3.5 m telescope. X-ray observations with XMM-Newton showed the host
star is inactive, with an X-ray-to-bolometric luminosity ratio of log 5.7 L L X bol » - . Joint analysis of the light
curves and RV measurements revealed that Gliese 12 b has a radius of 0.96 ± 0.05 R⊕,a3σ mass upper limit of
3.9 M⊕, and an equilibrium temperature of 315 ± 6 K assuming zero albedo. The transmission spectroscopy metric
(TSM) value of Gliese 12 b is close to the TSM values of the TRAPPIST-1 planets, adding Gliese 12 b to the small
list of potentially terrestrial, temperate planets amenable to atmospheric characterization with JWST.
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.
Travis Hills of MN is Making Clean Water Accessible to All Through High Flux ...Travis Hills MN
By harnessing the power of High Flux Vacuum Membrane Distillation, Travis Hills from MN envisions a future where clean and safe drinking water is accessible to all, regardless of geographical location or economic status.
Microbial interaction
Microorganisms interacts with each other and can be physically associated with another organisms in a variety of ways.
One organism can be located on the surface of another organism as an ectobiont or located within another organism as endobiont.
Microbial interaction may be positive such as mutualism, proto-cooperation, commensalism or may be negative such as parasitism, predation or competition
Types of microbial interaction
Positive interaction: mutualism, proto-cooperation, commensalism
Negative interaction: Ammensalism (antagonism), parasitism, predation, competition
I. Mutualism:
It is defined as the relationship in which each organism in interaction gets benefits from association. It is an obligatory relationship in which mutualist and host are metabolically dependent on each other.
Mutualistic relationship is very specific where one member of association cannot be replaced by another species.
Mutualism require close physical contact between interacting organisms.
Relationship of mutualism allows organisms to exist in habitat that could not occupied by either species alone.
Mutualistic relationship between organisms allows them to act as a single organism.
Examples of mutualism:
i. Lichens:
Lichens are excellent example of mutualism.
They are the association of specific fungi and certain genus of algae. In lichen, fungal partner is called mycobiont and algal partner is called
II. Syntrophism:
It is an association in which the growth of one organism either depends on or improved by the substrate provided by another organism.
In syntrophism both organism in association gets benefits.
Compound A
Utilized by population 1
Compound B
Utilized by population 2
Compound C
utilized by both Population 1+2
Products
In this theoretical example of syntrophism, population 1 is able to utilize and metabolize compound A, forming compound B but cannot metabolize beyond compound B without co-operation of population 2. Population 2is unable to utilize compound A but it can metabolize compound B forming compound C. Then both population 1 and 2 are able to carry out metabolic reaction which leads to formation of end product that neither population could produce alone.
Examples of syntrophism:
i. Methanogenic ecosystem in sludge digester
Methane produced by methanogenic bacteria depends upon interspecies hydrogen transfer by other fermentative bacteria.
Anaerobic fermentative bacteria generate CO2 and H2 utilizing carbohydrates which is then utilized by methanogenic bacteria (Methanobacter) to produce methane.
ii. Lactobacillus arobinosus and Enterococcus faecalis:
In the minimal media, Lactobacillus arobinosus and Enterococcus faecalis are able to grow together but not alone.
The synergistic relationship between E. faecalis and L. arobinosus occurs in which E. faecalis require folic acid
PPT on Direct Seeded Rice presented at the three-day 'Training and Validation Workshop on Modules of Climate Smart Agriculture (CSA) Technologies in South Asia' workshop on April 22, 2024.
Describing and Interpreting an Immersive Learning Case with the Immersion Cub...Leonel Morgado
Current descriptions of immersive learning cases are often difficult or impossible to compare. This is due to a myriad of different options on what details to include, which aspects are relevant, and on the descriptive approaches employed. Also, these aspects often combine very specific details with more general guidelines or indicate intents and rationales without clarifying their implementation. In this paper we provide a method to describe immersive learning cases that is structured to enable comparisons, yet flexible enough to allow researchers and practitioners to decide which aspects to include. This method leverages a taxonomy that classifies educational aspects at three levels (uses, practices, and strategies) and then utilizes two frameworks, the Immersive Learning Brain and the Immersion Cube, to enable a structured description and interpretation of immersive learning cases. The method is then demonstrated on a published immersive learning case on training for wind turbine maintenance using virtual reality. Applying the method results in a structured artifact, the Immersive Learning Case Sheet, that tags the case with its proximal uses, practices, and strategies, and refines the free text case description to ensure that matching details are included. This contribution is thus a case description method in support of future comparative research of immersive learning cases. We then discuss how the resulting description and interpretation can be leveraged to change immersion learning cases, by enriching them (considering low-effort changes or additions) or innovating (exploring more challenging avenues of transformation). The method holds significant promise to support better-grounded research in immersive learning.
The cost of acquiring information by natural selectionCarl Bergstrom
This is a short talk that I gave at the Banff International Research Station workshop on Modeling and Theory in Population Biology. The idea is to try to understand how the burden of natural selection relates to the amount of information that selection puts into the genome.
It's based on the first part of this research paper:
The cost of information acquisition by natural selection
Ryan Seamus McGee, Olivia Kosterlitz, Artem Kaznatcheev, Benjamin Kerr, Carl T. Bergstrom
bioRxiv 2022.07.02.498577; doi: https://doi.org/10.1101/2022.07.02.498577
CLASS 12th CHEMISTRY SOLID STATE ppt (Animated)eitps1506
Description:
Dive into the fascinating realm of solid-state physics with our meticulously crafted online PowerPoint presentation. This immersive educational resource offers a comprehensive exploration of the fundamental concepts, theories, and applications within the realm of solid-state physics.
From crystalline structures to semiconductor devices, this presentation delves into the intricate principles governing the behavior of solids, providing clear explanations and illustrative examples to enhance understanding. Whether you're a student delving into the subject for the first time or a seasoned researcher seeking to deepen your knowledge, our presentation offers valuable insights and in-depth analyses to cater to various levels of expertise.
Key topics covered include:
Crystal Structures: Unravel the mysteries of crystalline arrangements and their significance in determining material properties.
Band Theory: Explore the electronic band structure of solids and understand how it influences their conductive properties.
Semiconductor Physics: Delve into the behavior of semiconductors, including doping, carrier transport, and device applications.
Magnetic Properties: Investigate the magnetic behavior of solids, including ferromagnetism, antiferromagnetism, and ferrimagnetism.
Optical Properties: Examine the interaction of light with solids, including absorption, reflection, and transmission phenomena.
With visually engaging slides, informative content, and interactive elements, our online PowerPoint presentation serves as a valuable resource for students, educators, and enthusiasts alike, facilitating a deeper understanding of the captivating world of solid-state physics. Explore the intricacies of solid-state materials and unlock the secrets behind their remarkable properties with our comprehensive presentation.
PPT on Alternate Wetting and Drying presented at the three-day 'Training and Validation Workshop on Modules of Climate Smart Agriculture (CSA) Technologies in South Asia' workshop on April 22, 2024.
Craters, boulders and regolith of (101955) Bennu indicative of an old and dynamic surface
1. Articles
https://doi.org/10.1038/s41561-019-0326-6
1
Southwest Research Institute, Boulder, CO, USA. 2
Smithsonian Institution National Museum of Natural History, Washington, DC, USA. 3
Lunar and Planetary
Laboratory, University of Arizona, Tucson, AZ, USA. 4
The Johns Hopkins University Applied Physics Laboratory, Laurel, MD, USA. 5
Lockheed Martin Space,
Littleton, CO, USA. 6
Department of Geology, Rowan University, Glassboro, NJ, USA. 7
Planetary Science Institute, Tucson, AZ, USA. 8
Université Côte d’Azur,
Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, Nice, France. 9
Department of Aerospace Engineering, University of Maryland, College Park, MD,
USA. 10
INAF–Osservatorio Astronomico di Padova, Padova, Italy. 11
Hawaiʻi Institute of Geophysics and Planetology, University of Hawaiʻi at Mānoa, Honolulu,
HI, USA. 12
SETI Institute, Mountain View, CA, USA. 13
Space Science Institute, Boulder, CO, USA. 14
The Centre for Research in Earth and Space Science,
York University, Toronto, Ontario, Canada. 15
NASA Goddard Space Flight Center, Greenbelt, MD, USA. 16
Jet Propulsion Laboratory, California Institute of
Technology, Pasadena, CA, USA. 17
Department of Geoscience, University of Calgary, Calgary, AB, Canada. 18
NASA Ames Research Center, Moffett Field, CA,
USA. 19
Smead Department of Aerospace Engineering, University of Colorado, Boulder, CO, USA. 20
Department of Earth, Ocean and Atmospheric Sciences,
University of British Columbia, Vancouver, British Columbia, Canada. 21
A list of participants and their affiliations appears in the online version of the paper.
*e-mail: kwalsh@boulder.swri.edu
N
ASA’s OSIRIS-REx (Origins, Spectral Interpretation, Resource
Identification, and Security-Regolith Explorer) asteroid
sample return mission arrived at near-Earth asteroid (NEA)
(101955) Bennu on 3 December 2018. An imaging campaign dur-
ing the Approach phase of the mission collected panchromatic
images with the OSIRIS-REx Camera Suite (OCAMS) PolyCam
imager1–3
. Images collected by the OCAMS MapCam imager1
dur-
ing the Preliminary Survey phase of the mission were combined
with approach-phase imaging to produce a three-dimensional shape
model of the asteroid, revealing a spheroidal spinning-top shape with
a diameter of 492 ± 20 m (ref. 4
), as predicted by radar observations5
.
Over the past three decades, ground-based and spacecraft obser-
vations of asteroids, combined with theoretical and computational
advances, have transformed our understanding of small NEAs
(diameters <~10 km). Observations of NEA shapes, spins and sizes
combined with theoretical analyses that have provided insight into
their interior properties suggest that NEAs with diameters >~200 m
are ‘rubble piles’: gravitationally bound, unconsolidated fragments
with very low bulk tensile strength6,7
.
Rubble-pile asteroids originate from the main asteroid belt,
where catastrophic collisions between larger objects create a popu-
lation of gravitationally reaccumulated remnants8
. Small asteroids
have limited collisional lifetimes in the main belt (~0.1 to 1 billion
years), and their residence time in the main belt can be shorter than
the age of the Solar System due to Yarkovsky drift-induced ejec-
tion9
. After departing the main belt, NEAs are subject to further
evolutionary processes, such as rotational spin-up due to thermal
torques or tidal effects caused by close planetary flybys7
. These pro-
cesses can alter their global and surface morphologies. Studies of
the rubble-pile NEA (25143) Itokawa found large boulders exposed
on its surface, seemingly rapid degradation of impact craters and
evidence of substantial movement of surface material10
. This sug-
gests that Itokawa has undergone dynamical events10–12
that operate
on timescales shorter than its expected residence time in near-Earth
space (~10 million years)7
.
Detailed study of Bennu’s surface geology, particularly the
abundance of its craters and morphology of its boulders, provides
constraints on the surface age, which is important to disentangle
evolutionary processes that operated in near-Earth space from
those that operated in the main belt.
Rubble-pile nature of Bennu
The measured density of 1,190 kg m−3
and inferred high bulk
porosity of Bennu4,13
and the lack of either high surface slopes or
Craters, boulders and regolith of (101955) Bennu
indicative of an old and dynamic surface
K. J. Walsh 1
*, E. R. Jawin2
, R.-L. Ballouz 3
, O. S. Barnouin 4
, E. B. Bierhaus5
, H. C. Connolly Jr. 6
,
J. L. Molaro7
, T. J. McCoy2
, M. Delbo’8
, C. M. Hartzell 9
, M. Pajola 10
, S. R. Schwartz3
, D. Trang11
,
E. Asphaug3
, K. J. Becker 3
, C. B. Beddingfield12
, C. A. Bennett3
, W. F. Bottke1
, K. N. Burke 3
, B. C. Clark13
,
M. G. Daly 14
, D. N. DellaGiustina 3
, J. P. Dworkin 15
, C. M. Elder16
, D. R. Golish3
, A. R. Hildebrand17
,
R. Malhotra3
, J. Marshall12
, P. Michel 8
, M. C. Nolan 3
, M. E. Perry4
, B. Rizk 3
, A. Ryan8
, S. A. Sandford18
,
D. J. Scheeres 19
, H. C. M. Susorney20
, F. Thuillet8
, D. S. Lauretta3
and The OSIRIS-REx Team21
Small, kilometre-sized near-Earth asteroids are expected to have young and frequently refreshed surfaces for two reasons:
collisional disruptions are frequent in the main asteroid belt where they originate, and thermal or tidal processes act on them
once they become near-Earth asteroids. Here we present early measurements of numerous large candidate impact craters on
near-Earth asteroid (101955) Bennu by the OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, and Security-
Regolith Explorer) mission, which indicate a surface that is between 100 million and 1 billion years old, predating Bennu’s
expected duration as a near-Earth asteroid. We also observe many fractured boulders, the morphology of which suggests an
influence of impact or thermal processes over a considerable amount of time since the boulders were exposed at the surface.
However, the surface also shows signs of more recent mass movement: clusters of boulders at topographic lows, a deficiency
of small craters and infill of large craters. The oldest features likely record events from Bennu’s time in the main asteroid belt.
Nature Geoscience | www.nature.com/naturegeoscience
2. Articles NaTuRE GEOScIEncE
substantial topographic relief indicate that Bennu is a rubble pile.
Bennu’s density requires 25–50% macroporosity if it is constructed
primarily of CI (bulk density of 1,570 kg m−3
) or CM (bulk density
of 2,200 kg m−3
) chondrite-like material14
. If the microporosity pres-
ent in these meteorite classes is also considered15
, the total porosity
of Bennu may be as high as 60%. In addition, the slope at each point
on the surface of Bennu—determined from the combination of the
shape, mass and spin state—shows a relaxed distribution with val-
ues averaging approximately 17°, and almost entirely below typical
angles of approximately 30° allowed by the angle of repose of terres-
trial materials and found on other similarly sized NEAs13,16
.
Boulders dominate the local topography of Bennu, some with
heights >20 m (Fig. 1a). The most prominent boulder on Bennu
was first detected with ground-based radar and estimated to be 10
to 20 m in diameter2
. This same boulder is apparent in PolyCam
images and measures approximately 56 m in its longest dimension
(Fig. 1a). There are three identified boulders with long axes exceed-
ing 40 m and more than 200 boulders larger than 10 m2
. Boulders in
the tens-of-metres size range are larger than plausible ejecta from
any of the large crater candidates on Bennu17
, and also unlikely to
be meteorites that Bennu could have accreted in its current orbit,
suggesting instead that their origins trace back to the formation of
Bennu in the asteroid belt.
Boulders on Bennu have albedo and colour diversity1
, with some
showing these differences within distinct metre-sized clasts in an
otherwise unfragmented rock. We interpret such assemblages as
impact breccias (Fig. 1b). Processes capable of creating breccias
spanning tens of metres with metre-sized clasts imply energetic
events that far exceed what Bennu can support18,19
.
The possible inherited origin of Bennu’s largest boulders sup-
ports the idea that rubble piles form as reaccumulated remnants
of disruptive collisions of larger asteroids in the main asteroid
belt8
. Furthermore, the existence of breccias suggests that they
are a record of the parent body’s accretion, that they formed dur-
ing impact regolith gardening on the surface of that parent body
or that they originated during the catastrophic disruption event
that formed Bennu. The noted albedo and colour diversity of the
boulders, and the distinct metre-scale components visible in some
of them, may point to the compositional diversity of Bennu’s parent
body and/or its catastrophic impactor.
Boulder geology of Bennu
The spatial distribution of boulders on the surface of Bennu is not
uniform. We find concentrations of boulders in some local topo-
graphic lows4
(tens-of-metres elevation differences relative to the
surrounding terrain), with boulder abundances up to an order of
magnitude greater than the global average (Fig. 2). These collec-
tions of boulders stand in contrast to topographic lows on Itokawa,
which are distinct for their lack of large boulders and collections of
small grains11
.
ThebouldersonBennu’ssurfacealsoexhibitdiversityinsize,geo-
logic context and morphology. To date, boulders >8 m in diameter
have been adequately resolved with PolyCam images, for which we
have measured a size-frequency distribution best fit with a power-
law index of –2.9 ± 0.3 (ref. 2
). Many of these boulders appear to be
resting on top of the surface, while some are partially buried, point-
ing to active burial and/or exhumation processes. Several examples
of imbricated boulders have been identified, although these loca-
tions are smaller in extent than the imbricated regions observed
on Itokawa11
, with no obvious correlation between imbrication and
fine-grained deposits. Both rounded and angular boulders are pres-
ent on the surface, which may suggest a variety of formation mecha-
nisms, compositions and/or boulder evolutionary processes.
We observe fractured boulders exhibiting multiple fracture
types. Some of the most dramatic examples include large, linear
fractures that appear to split boulders into two or more pieces
(Fig. 1c,d). These occur at all resolvable scales and within some
of the largest boulders on the surface. In contrast, other boulders
exhibit nonlinear fractures that suggest some interaction between
the fracture-driving mechanisms and the rock bulk structure
(Fig. 1e). We also found examples of discrete, yet tightly clustered
metre-scale boulders that appear to have fractured in situ, and
remain in clusters with minimal displacement (Fig. 1f). Complex
networks of fractures also occur in some boulders (Fig. 1c,d), with
many deep fractures crossing each other at various angles, although
some are clearly linear. These numerous and morphologically var-
ied fractures may be produced by one or a combination of processes,
such as large-scale impact events, micrometeoroid impacts and
thermal fatigue. The latter two processes may also be responsible
for the shallow fractures and surficial features observed on visibly
textured boulders, which indicate exfoliation, near-surface disag-
gregation or regolith production processes (for example, refs. 20–22
).
20 m
N
8 mN
N 14 mN12 m
10 m
N
a
c
b
d
e f
10 m
N
Fig. 1 | The boulders of Bennu can be large and are sometimes fractured
or brecciated. a, A boulder located at 48° S and 125° E with a diameter of
approximately 56 m and height of over 20 m relative to the surrounding
surface of Bennu. b, A brecciated boulder located at 6° S and 247° E that
is approximately 21 m in diameter with large constituent pieces showing
measurable geometric albedo differences1
. c, A boulder with a diameter
of approximately 40 m located at 42° N and 129° E that shows a complex
web of large fractures. d, A boulder with a diameter of approximately
20 m located at 11° S and 258° E with a single linear fracture. e, A boulder
with a diameter of approximately 10 m located at 5° N and 310° E with a
nonlinear fracture (red arrow). f, A cluster of metre-sized boulders centred
at 44° N and 111° E. Images taken on: a, 1 December 2018 from a spacecraft
distance of 31.5 km; b,d, 2 December 2018 from a distance of 24.0 km;
c, 2 December 2018 from a distance of 23.8 km; e, 2 December 2018 from
a distance of 24.2 km; f, 2 December 2018 from a distance of 23.6 km.
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3. ArticlesNaTuRE GEOScIEncE
Although boulder fracture could potentially represent past pro-
cessing on Bennu’s parent body, the abundance of fractured boul-
ders and some cases where boulders appear to have disaggregated
in situ points to surface processes active in Bennu’s recent geologic
history, since it evolved to a near-Earth orbit. However, these frac-
ture formation mechanisms need time to operate, suggesting that
the surface has not been dynamically refreshed since Bennu’s transi-
tion from the main belt to its near-Earth orbit, where a typical NEA’s
dynamical lifetime is on the order of 10 million years23
. Breakdown
due to micrometeoroid bombardment and thermal fatigue is pre-
dicted to be faster and slower, respectively, in the main belt than
in near-Earth space20,22,24
. However, the relative efficiencies of these
and other active processes are not well constrained, making it dif-
ficult to use fractures to assess absolute surface age. Some processes
also act over multiple timescales, such as thermal fatigue, which
may generate fractures over different spatial scales owing to diurnal
and annual thermal cycles.
Craters of Bennu
Bennu has experienced a number of impacts that have transformed
its surface. We have identified several tens of candidate impact cra-
ters, which range in size from approximately 10 m to more than
150 m in diameter. The characteristics of distinct candidate impact
craters include circular features with raised rims and depressed
floors, and/or clear textural differences (apparent concentration
or lack of boulders) between the interior and exterior of the crater.
Less-distinct candidate craters have subdued rims or an absence of
raised rims, shallow interiors, and lack of contrast between the inte-
rior and exterior boulder populations. Based on current image data,
we have identified 12 distinct, and at least 40 less-distinct, candidate
craters. Notably, several large distinct craters are located on Bennu’s
equatorial ridge, suggesting that the ridge is an old feature (Fig. 3).
We used the population of large distinct candidate craters (diam-
eter D > 50 m) to estimate the age of Bennu’s surface. Assuming
that the craters record impact events, they are primarily a record
of Bennu’s history in the main asteroid belt25
. Crater scaling laws
can convert impact parameters to crater diameters, although for
small rubble-pile bodies there is added uncertainty due to their
microgravity regime26,27
. By applying Bennu’s physical properties
to these scaling relationships (for example, a crater scaling law for
dry soil with a strength of 0.18 MPa (ref. 26
)), we can estimate the
ratio of crater to projectile diameters. The size-frequency distri-
bution of main-belt projectiles striking Bennu is assumed to fol-
low the collisional evolution results25
, while the intrinsic collision
probability of Bennu with a main-belt projectile is assumed to be
fairly similar to Gaspra, a relatively low inclination asteroid residing
in the innermost region of the main belt (where the intrinsic
collisional probability is Pi = 2.8 × 10−18
km−2
yr−1
)28
. These compo-
nents, when combined with Bennu’s cross-section28
, can be fit to
Bennu’s D > 50 m craters. We find that it would take between 100
million and 1 billion years to explain the origin of Bennu’s largest
crater candidates (Fig. 3d).
However, cratering into low-strength material under low-grav-
ity conditions may lead to larger crater diameters, which in turn
could lead to younger age estimates27
. Conversely, cratering into
high-porosity material may lead to reduced diameters and older age
estimates29
. It is possible that determining the surface exposure age
of the returned sample will quantitatively constrain Bennu’s crater
retention age and provide a better understanding of which aspects
play dominant roles in crater formation on Bennu and other high-
porosity, low-strength targets.
The imaging and topographic data allowed identification of
craters approximately 10 m and larger. The observations show a
depletion of small craters (~10 m < D < 50 m) relative to expecta-
tions based on the production rate of large craters (Fig. 3d). The
depletion of small craters has also been found on other NEAs
including Itokawa and Eros30,31
. The prevalence of boulders on
the surface can potentially stifle the formation of small craters,
whereby impactors strike and break boulders rather than making
craters32
. Conversely, the depletion of small craters may reflect,
0° 50° E 100° E 150° E 200° E 250° E 300° E 350° E
Longitude
80° S
60° S
40° S
20° S
0
20° N
40° N
60° N
80° N
Latitude
0
N(D>8m,within25m)perkm2
1,000
2,000
3,000
4,000
5,000
6,000
7,000
8,000
Fig. 2 | Boulder abundance map of the surface of Bennu. The abundance of
boulders for each location on the surface of Bennu based on a 49,152-facet
shape model of the surface, where the boulder abundance (N) is calculated
by counting the number of boulders larger than 8 m within a radius of 25 m
in each facet and then normalized to square kilometre.
15 mN
9 mN
30 mN
a
c
b
1
100
N(>D)km–2
Crater diameter (m)
1 Gyr
500 Myr
100 Myr
All
Distinct
10
10
d
Fig. 3 | Examples of Bennu’s craters. a, A feature on Bennu’s surface
that meets all of the criteria to be considered a distinct candidate crater,
including clear topography associated with its rim. This candidate crater
is centred at 3° S and 152° E and has a diameter of 81 m. b, A distinct
candidate crater located at 5° S and 126° E with diameter of 44 m differs in
texture between the inside and outside of its rim and shows a distinct lack
of boulders. c, Example of a less-distinct candidate crater located at 54° N
and 68° E, with some textural differences between the inside and outside
of the circular feature, but that shows only hints of a circular shape with no
clear topography. d, The established ‘distinct’ candidate craters provide a
lower bound on age by comparing their distributions to the expected crater
production function (see Methods), and we use the entire population of
less-distinct candidate craters to estimate an upper bound. In both groups,
the change in size-frequency distribution appears around D = 50 m. Images
taken on: a,b, 2 December 2018 from a distance of 23.7 km; c, 2 December
2018 from a distance of 23.5 km.
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4. Articles NaTuRE GEOScIEncE
as previously postulated, crater erasure due to surface material
movement and/or seismic shaking33,34
. There are clear examples on
some large candidate craters on Bennu of material movement and
crater infill, where the thickness of the fill layer is comparable to
the depth of small craters (Fig. 4)4
.
Regolith of Bennu
The interiors of many small candidate impact craters (D < 20 m) are
largely devoid of resolvable boulders (Fig. 3). These locations may
be reservoirs for smaller particles produced or exposed during the
crater formation process. Similarly, boulder-fracturing processes or
abrasion and mechanical erosion between boulders during surface
material movement could each contribute to the production of fine
grains more widely across the surface of Bennu.
Thereissomeevidencethatfine-grainedmaterial(ofthecentime-
tre-scale sizes that are ingestible by the OSIRIS-REx sample mecha-
nism35
and of smaller, micrometre-scale sizes) is present despite not
being resolved with current imaging. The measured thermal inertia
is consistent with a population of centimetre-sized particles2
. The
phase reddening observed with the MapCam images suggest some
photometric contribution by micrometre-sized particles2
. Thermal
emission spectra14
exhibit evidence of a surface dominated by parti-
cles greater than 125 µm at spatial scales of approximately 80 m, but
these data cannot provide more specific information on the range of
particle sizes greater than 125 µm or rule out the presence of a small
fraction of particles smaller than 125 µm.
Finally, certain regions only a few metres in size have large albedo
differences and lack observable boulders, suggesting that they are
dominated by unresolved (<1 m) particles1
. Other fine-particulate
patches appear as surficial layers indiscriminately draped over boul-
der and inter-boulder areas alike2
. However, low-albedo deposits do
not mask the outlines of boulders. The dark material comprising
these patches may be dust or fine particles.
History of Bennu
The large boulders on the surface of Bennu may provide informa-
tion about the composition and geology of its parent body, as well
as the collision that disrupted it. The observed impact breccias
may have formed during the evolution of its parent body, through
repeated impact events on its surface over most of Solar System his-
tory, or during the large impact event that resulted in the formation
of Bennu. Alternatively, these breccias may even date to the accre-
tion of the original parent body in the protoplanetary disk.
The retention of large craters on Bennu’s equatorial ridge
requires that the surface age predates the expected approximately
10-million-year duration as a NEA. There is no clear geologic indi-
cation of the process that formed the ridge, and given its relation
to the large craters it could be a feature preserved from the forma-
tion of Bennu36
, which would make it the oldest feature on its sur-
face4,13,31
. Bennu’s surface therefore also recorded processes from its
time in the main belt; the formation timescales of the largest craters
suggest that Bennu recorded hundreds of millions of years of his-
tory during this period.
Bennu retains very old craters despite evidence of continued and
varied surface evolution. The processes that have removed small
craters may be size limited or spatially localized and therefore can-
not efficiently erase larger craters. The crater infill observed on the
largest distinct crater has deposited an approximately 5-m-thick
layer of material inside the crater and has partially degraded a large
swath of the crater rim (Fig. 4). If surface material movement of
this scale were to act widely and frequently, it could contribute to
large-scale resurfacing of the asteroid. However, the old age of the
surface of Bennu indicates that this type of event may either be
localized, or of low frequency, possibly occurring only during its
time as an NEA.
Resurfacing and surface movement will have influenced and
resorted the fine-grained surface material that is the final target of
the OSIRIS-REx mission37
. The returned sample of this material
will tell us about processes that occurred since Bennu has been a
NEA, while Bennu was in the main belt, and likely processes that
occurred on its original parent body and in the solar nebula long
before Bennu formed.
Online content
Any methods, additional references, Nature Research reporting
summaries, source data, statements of data availability and asso-
ciated accession codes are available at https://doi.org/10.1038/
s41561-019-0326-6.
260° E 270° E 280° E 290° E
Longitude
30° S
25° S
20° S
15° S
10° S
5° S
0
5° N
10° N
15° N
Latitude
5 10 15 20 25
Elevation (m)
1
2
3
4
250° E
0
5
10
15
20
25
30
0 20 40 60 80 100Elevation(m)
Distance from crater centre (m)
1
2
3
4
N
40 m
ca b
Fig. 4 | Flow of material into a D = 160 m candidate crater. a, A large candidate crater is centred near the equator at 8° S and 269° E, and initial
measurements indicate a diameter of 160 m. The drawn circle outlines the crater rim and four dotted lines indicate profiles along which elevation was
extracted radially from the centre of the crater outward. b, The elevation profiles for the different regions of the crater, where the profiles 1 and 2 show
that the southwest region of the crater is elevated relative to the rest of the crater shown with profiles 3 and 4. The mass movement appears to have
overtopped the crater rim and covered parts of the crater with metres of material. c, Image showing the relationship between the material flow and the
candidate crater. White arrows indicate the crater rim, and yellow arrows indicate the edge of the flow which has entered the crater from the west (the
flow correlates with the elevated portion of topographic profiles 1 and 2). Stratigraphic relationships show that the flow occurred after the formation of
the crater. Leftmost yellow arrow indicates additional material movement that has partly buried the westernmost portion of a larger boulder (which is also
shown in Fig. 1c). Image used for c was taken on 1 December 2018 from a distance of 31.8 km.
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6. Articles NaTuRE GEOScIEncE
craters to estimate a range of possible surface ages based on the impactor size
distribution found in the main belt, an average main-belt impact probability and
impact velocity (Pi = 2.8 × 10–18
km–2
yr–1
and vi = 5.3 km s–1
)25,39
, and a crater scaling
law for dry soil with a strength of 0.18 MPa (ref. 26
). The clearly established ‘distinct’
candidate craters, normalized to one square kilometre, provide a lower bound on
age, and we use the entire population of less-distinct candidate craters to estimate
an upper bound. In both groups, the change in size-frequency distribution appears
around D = 50 m. Image ocams20181202t083822s735_pol_iofl2pan_64172 was
used for Fig. 3a,b and was taken on 2 December 2018 from a spacecraft range of
23.7 km. Image for Fig. 3c was ocams20181202t091159s321_pol_iofl2pan_64104
and was taken on 2 December 2018 from a spacecraft range of 23.5 km. Image
ocams20181201t051455s588_pol_iofl2pan_63071 was used for Fig. 4c and was
taken on 1 December 2018 from a spacecraft distance of 31.8 km.
Many of the geologic assessments relied on elevation, which was derived from
shape model v14. The construction of the shape model, and different versions of the
shape model, and calculation of elevation is described in detail in a companion paper4
.
Data availability
Raw through to calibrated datasets 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, global mosaics and elevation
maps, will be available in the PDS one year after departure from the asteroid.
References
38. Ernst, C. M., Barnouin, O. S. & Daly, R. T. The Small Body Mapping Tool
(SBMT) for accessing, visualizing, and analyzing spacecraft data in three
dimensions. In Lunar Planetary Sci. Conf. 49 abstr. 1043 (2018).
39. Marchi et al. The cratering history of (2867) Steins. Planet. Space Sci. 58,
1116–1123 (2010).
Methods
Initial boulder identification was carried out following the methods outlined
in ref. 2
. Subsequent detailed mapping and geologic analyses of boulders were
performed by a visual analysis of PolyCam and MapCam data using the Small
Body Mapping Tool (SBMT), which projects spacecraft images onto a shape
model38
. Boulders were mapped by drawing an ellipse around the resolved boulder
margins; this method allows for the analysis of both long and intermediate axis
lengths, as well as boulder orientation. Boulders were viewed under a range of
viewing geometries including various phase angles and illumination angles.
Detailed boulder morphology was assessed using a combination of unprojected
images which facilitated fine-scale analyses, and projected images within SBMT,
which provides geologic context. Boulder abundance (Fig. 2) was calculated using
a 49,152-facet shape model4
, where the boulder abundance was calculated by
counting the number of boulders larger than 8 m within a 25 m radius in each facet
and then normalizing to 1 km2
. Image for Fig. 1a is ocams20181201t055746s307_
pol_iofl2pan_63551 taken on 1 December 2018 from a spacecraft distance of
31.5 km. Fig. 1b,d is from image ocams20181202t072303s706_pol_iofl2pan_63785
taken on 2 Decemeber 2018 with a spacecraft distance 24.0 km. Fig. 1c is taken
from image ocams20181202t082747s619_pol_iofl2pan_63714 taken on 2
December 2018 with a spacecraft distance of 23.8 km. Fig. 1e is taken from image
20181202T064001S485_pol_iofL2pan taken on 2 December 2018 with a spacecraft
distance of 24.2 km. Fig. 1f is taken from image20181202T084918S806_pol_
iofL2pan taken on 2 December 2018 with a spacecraft distance of 23.6 km.
Crater identification and measurement was performed using a combination
of projected and unprojected PolyCam and MapCam images, as well as
stereophotoclinometry-derived topography data4
. All mapping was carried out in
SBMT by mapping ellipses around the maximum extent of the resolvable crater
rim. Multiple members of the team mapped the surface for craters and only those
mapped by multiple members as distinct crater candidates were counted in the
‘distinct’ category for the purposes of analysis. All mapped individual craters were
included in the ‘non-distinct’ group. To calculate surface age, we used the largest
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7. ArticlesNaTuRE GEOScIEncE
The OSIRIS-REx Team
D. E. Highsmith22
, J. Small22
, D. Vokrouhlický23
, N. E. Bowles24
, E. Brown24
, K. L. Donaldson Hanna24
,
T. Warren24
, C. Brunet25
, R. A. Chicoine25
, S. Desjardins25
, D. Gaudreau25
, T. Haltigin25
,
S. Millington-Veloza25
, A. Rubi25
, J. Aponte26
, N. Gorius26
, A. Lunsford26
, B. Allen27
, J. Grindlay27
,
D. Guevel27
, D. Hoak27
, J. Hong27
, D. L. Schrader28
, J. Bayron29
, O. Golubov30
, P. Sánchez30
, J. Stromberg31
,
M. Hirabayashi32
, C. M. Hartzell9
, S. Oliver33
, M. Rascon33
, A. Harch34
, J. Joseph34
, S. Squyres34
,
D. Richardson35
, J. P. Emery36
, L. McGraw36
, R. Ghent37
, R. P. Binzel38
, M. M. Al Asad20
, C. L. Johnson7,20
,
L. Philpott20
, H. C. M. Susorney20
, E. A. Cloutis39
, R. D. Hanna40
, H. C. Connolly Jr.6
, F. Ciceri17
,
A. R. Hildebrand17
, E.-M. Ibrahim17
, L. Breitenfeld41
, T. Glotch41
, A. D. Rogers41
, B. E. Clark42
, S. Ferrone42
,
C. A. Thomas43
, H. Campins44
, Y. Fernandez44
, W. Chang45
, A. Cheuvront46
, D. Trang11
, S. Tachibana47
,
H. Yurimoto47
, J. R. Brucato48
, G. Poggiali48
, M. Pajola10
, E. Dotto49
, E. Mazzotta Epifani49
,
M. K. Crombie50
, C. Lantz51
, M. R. M. Izawa52
, J. de Leon53
, J. Licandro53
, J. L. Rizos Garcia53
, S. Clemett54
,
K. Thomas-Keprta54
, S. Van wal55
, M. Yoshikawa55
, J. Bellerose16
, S. Bhaskaran16
, C. Boyles16
,
S. R. Chesley16
, C. M. Elder16
, D. Farnocchia16
, A. Harbison16
, B. Kennedy16
, A. Knight16
,
N. Martinez-Vlasoff16
, N. Mastrodemos16
, T. McElrath16
, W. Owen16
, R. Park16
, B. Rush16
, L. Swanson16
,
Y. Takahashi16
, D. Velez16
, K. Yetter16
, C. Thayer56
, C. Adam57
, P. Antreasian57
, J. Bauman57
, C. Bryan57
,
B. Carcich57
, M. Corvin57
, J. Geeraert57
, J. Hoffman57
, J. M. Leonard57
, E. Lessac-Chenen57
, A. Levine57
,
J. McAdams57
, L. McCarthy57
, D. Nelson57
, B. Page57
, J. Pelgrift57
, E. Sahr57
, K. Stakkestad57
,
D. Stanbridge57
, D. Wibben57
, B. Williams57
, K. Williams57
, P. Wolff57
, P. Hayne58
, D. Kubitschek58
,
M. A. Barucci59
, J. D. P. Deshapriya59
, S. Fornasier59
, M. Fulchignoni59
, P. Hasselmann59
, F. Merlin59
,
A. Praet59
, E. B. Bierhaus5
, O. Billett5
, A. Boggs5
, B. Buck5
, S. Carlson-Kelly5
, J. Cerna5
, K. Chaffin5
,
E. Church5
, M. Coltrin5
, J. Daly5
, A. Deguzman5
, R. Dubisher5
, D. Eckart5
, D. Ellis5
, P. Falkenstern5
,
A. Fisher5
, M. E. Fisher5
, P. Fleming5
, K. Fortney5
, S. Francis5
, S. Freund5
, S. Gonzales5
, P. Haas5
,
A. Hasten5
, D. Hauf5
, A. Hilbert5
, D. Howell5
, F. Jaen5
, N. Jayakody5
, M. Jenkins5
, K. Johnson5
,
M. Lefevre5
, H. Ma5
, C. Mario5
, K. Martin5
, C. May5
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, C. Miller5
, G. Miller5
,
A. Mirfakhrai5
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,
M. Skeen5
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,
S. Bendall3
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, D. Blum3
, W. V. Boynton3
, J. Brodbeck3
, K. N. Burke3
,
M. Chojnacki3
, A. Colpo3
, J. Contreras3
, J. Cutts3
, C. Y. Drouet d’Aubigny3
, D. Dean3
, D. N. DellaGiustina3
,
B. Diallo3
, D. Drinnon3
, K. Drozd3
, H. L. Enos3
, R. Enos3
, C. Fellows3
, T. Ferro3
, M. R. Fisher3
, G. Fitzgibbon3
,
M. Fitzgibbon3
, J. Forelli3
, T. Forrester3
, I. Galinsky3
, R. Garcia3
, A. Gardner3
, D. R. Golish3
, N. Habib3
,
D. Hamara3
, D. Hammond3
, K. Hanley3
, K. Harshman3
, C. W. Hergenrother3
, K. Herzog3
, D. Hill3
,
C. Hoekenga3
, S. Hooven3
, E. S. Howell3
, E. Huettner3
, A. Janakus3
, J. Jones3
, T. R. Kareta3
, J. Kidd3
,
K. Kingsbury3
, S. S. Balram-Knutson3
, L. Koelbel3
, J. Kreiner3
, D. Lambert3
, D. S. Lauretta3
, C. Lewin3
,
B. Lovelace3
, M. Loveridge3
, M. Lujan3
, C. K. Maleszewski3
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22
Aerospace Corporation, Chantilly, VA, USA. 23
Astronomical Institute, Charles University, Prague, Czech Republic. 24
Atmospheric, Oceanic and Planetary
Physics, University of Oxford, Oxford, UK. 25
Canadian Space Agency, Saint-Hubert, Quebec, Canada. 26
Catholic University of America, Washington, DC,
USA. 27
Center for Astrophysics, Harvard University, Cambridge, MA, USA. 28
Center for Meteorite Studies, Arizona State University, Tempe, AZ, USA.
29
City University of New York, New York, NY, USA. 30
Colorado Center for Astrodynamics Research, University of Colorado, Boulder, CO, USA.
31
Commonwealth Scientific and Industrial Research Organisation (CSIRO), Canberra, Australian Capital Territory, Australia. 32
Department of Aerospace
Engineering, Auburn University, Auburn, AL, USA. 33
Department of Astronomy and Steward Observatory, University of Arizona, Tuscon, AZ, USA.
34
Department of Astronomy, Cornell University, Ithaca, NY, USA. 35
Department of Astronomy, University of Maryland, College Park, MD, USA.
36
Department of Earth and Planetary Sciences, University of Tennessee, Knoxville, TN, USA. 37
Department of Earth Sciences, University of Toronto,
Toronto, Ontario, Canada. 38
Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA, USA.
39
Department of Geography, University of Winnipeg, Winnipeg, Manitoba, Canada. 40
Department of Geological Sciences, Jackson School of Geosciences,
University of Texas, Austin, TX, USA. 41
Department of Geosciences, Stony Brook University, Stony Brook, NY, USA. 42
Department of Physics and
Astronomy, Ithaca College, Ithaca, NY, USA. 43
Department of Physics and Astronomy, Northern Arizona University, Flagstaff, AZ, USA. 44
Department of
Physics, University of Central Florida, Orlando, FL, USA. 45
Edge Space Systems, Greenbelt, MD, USA. 46
General Dynamics C4 Systems, Denver, CO, USA.
47
Hokkaido University, Sapporo, Japan. 48
INAF–Astrophysical Observatory of Arcetri, Florence, Italy. 49
INAF–Osservatorio Astronomico di Roma, Rome,
Italy. 50
Indigo Information Services, Tucson, AZ, USA. 51
Institut d’Astrophysique Spatiale, CNRS/Université Paris Sud, Orsay, France. 52
Institute for Planetary
Materials, Okayama University–Misasa, Misasa, Japan. 53
Instituto de Astrofísica de Canarias and Departamento de Astrofísica, Universidad de La
Laguna, Tenerife, Spain. 54
Jacobs Technology, Houston, TX, USA. 55
JAXA Institute of Space and Astronautical Science, Sagamihara, Japan. 56
Kavli Institute
for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA, USA. 57
KinetX Aerospace, Inc., Simi Valley, CA, USA.
58
Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO, USA. 59
LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne
Université, Univ. Paris Diderot, Sorbonne Paris Cité, Meudon, France. 60
Macdonald, Dettwiler, and Associates, Brampton, Ontario, Canada. 61
Malin Space
Science Systems, San Diego, CA, USA. 62
Mars Space Flight Facility, Arizona State University, Tempe, AZ, USA. 63
Mines ParisTech, Paris, France. 64
Nagoya
University, Nagoya, Japan. 65
NASA Headquarters, Washington, DC, USA. 66
NASA Johnson Space Center, Houston, TX, USA. 67
NASA Langley Research
Center, Hampton, VA, USA. 68
NASA Marshall Space Flight Center, Huntsville, AL, USA. 69
Research School of Earth Sciences, Australian National University,
Canberra, Australian Capital Territory, Australia. 70
Royal Ontario Museum, Toronto, Ontario, Canada. 71
School of Earth and Planetary Sciences, Curtin
University, Perth, Western Australia, Australia. 72
School of Earth and Space Exploration, Arizona State University, Tempe, AZ, USA. 73
School of Physical
Sciences, The Open University, Milton Keynes, UK. 74
Southwest Meteorite Laboratory, Payson, AZ, USA. 75
Space Systems Laboratory, Department of
Aeronautics and Astronautics, Massachusetts Institute of Technology, Cambridge, MA, USA. 76
US Geological Survey Astrogeology Science Center,
Flagstaff, AZ, USA. 77
London Stereoscopic Company, London, UK. 78
Université de Lorraine, Nancy, France.
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