This document summarizes a study analyzing the effects of target material properties and layering on determining crater ages for the Raditladi and Rachmaninoff basins on Mercury. The authors derive model ages of about 3.6 billion years for Rachmaninoff basin and 1.1 billion years for Raditladi basin. They also constrain the age of smooth plains within the basin floors, suggesting volcanic activity on Mercury may have continued until around 1 billion years ago or less. The study addresses the importance of considering terrain parameters such as mechanical properties and layering in the age determination process.
Ancient igneous intrusions_and_early_expansion_of_the_moon_revealed_by_grailSérgio Sacani
1) Application of gravity gradiometry to data from the GRAIL mission revealed numerous linear gravity anomalies on the Moon with lengths of hundreds of kilometers.
2) Inversion of the anomalies indicates they are dense vertical intrusions or dikes formed by ancient magmatism during extension of the lunar lithosphere before the end of heavy bombardment.
3) The distribution, orientation, and size of the intrusions suggest they formed as the Moon's radius increased by 0.6-4.9 km early in its history, consistent with predictions of thermal evolution models.
This document provides a summary of an anonymous student's education and research experience. The student received their PhD from MIT in earth and planetary sciences, focusing on high degree mantle melts. They are currently a postdoctoral researcher at MIT studying magma production in the Aleutian arc. The student has extensive experience conducting high-pressure experiments and geochemical modeling to study mantle melting processes.
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
The petrochemistry of_jake_m_a_martian_mugeariteSérgio Sacani
The rock "Jake_M" was the first rock analyzed by Curiosity on Mars. It has a distinct chemical composition compared to other known Martian rocks. Jake_M has a basaltic composition but is alkaline, with over 15% normative nepheline content. Its chemical makeup is similar to terrestrial mugearites, fractionated alkaline rocks found at ocean islands and rifts. This suggests Jake_M formed through extensive fractional crystallization of an alkaline magma at elevated pressure, possibly with water. The discovery of an alkaline rock expands the diversity of known Martian igneous compositions.
A habitable fluvio_lacustrine_at_gale_crater_mars1Sérgio Sacani
The Curiosity rover discovered fine-grained sedimentary rocks in Yellowknife Bay, Gale crater, Mars that are inferred to represent an ancient lake environment. Analysis found the environment would have been habitable by microorganisms, with a neutral pH, low salinity, and variable redox states of iron and sulfur. Key biogenic elements like carbon, hydrogen, oxygen, sulfur, nitrogen and phosphorus were detected, suggesting the environment could have supported a Martian biosphere based on chemolithoautotrophy. The habitable conditions were likely present for hundreds to tens of thousands of years. These results highlight the potential for fluvial-lacustrine environments on Mars after the Noachian period to
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
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 document discusses soft rocks in Argentina. It begins by defining soft rocks as sedimentary, pyroclastic, chemical sedimentary, and some metamorphic rocks with low to moderate lithification and minerals with Mohs hardness less than 3.5, such as limestone, gypsum, and shale. In Argentina, soft rocks are widespread but have not received much study despite impacts on engineering projects like dams and tunnels. The document reviews various studies of soft rock properties in Argentina, finding strengths typically between 2 and 38 MPa and high deformability. More research is needed to better understand the geomechanics of these weak rocks.
Ancient igneous intrusions_and_early_expansion_of_the_moon_revealed_by_grailSérgio Sacani
1) Application of gravity gradiometry to data from the GRAIL mission revealed numerous linear gravity anomalies on the Moon with lengths of hundreds of kilometers.
2) Inversion of the anomalies indicates they are dense vertical intrusions or dikes formed by ancient magmatism during extension of the lunar lithosphere before the end of heavy bombardment.
3) The distribution, orientation, and size of the intrusions suggest they formed as the Moon's radius increased by 0.6-4.9 km early in its history, consistent with predictions of thermal evolution models.
This document provides a summary of an anonymous student's education and research experience. The student received their PhD from MIT in earth and planetary sciences, focusing on high degree mantle melts. They are currently a postdoctoral researcher at MIT studying magma production in the Aleutian arc. The student has extensive experience conducting high-pressure experiments and geochemical modeling to study mantle melting processes.
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
The petrochemistry of_jake_m_a_martian_mugeariteSérgio Sacani
The rock "Jake_M" was the first rock analyzed by Curiosity on Mars. It has a distinct chemical composition compared to other known Martian rocks. Jake_M has a basaltic composition but is alkaline, with over 15% normative nepheline content. Its chemical makeup is similar to terrestrial mugearites, fractionated alkaline rocks found at ocean islands and rifts. This suggests Jake_M formed through extensive fractional crystallization of an alkaline magma at elevated pressure, possibly with water. The discovery of an alkaline rock expands the diversity of known Martian igneous compositions.
A habitable fluvio_lacustrine_at_gale_crater_mars1Sérgio Sacani
The Curiosity rover discovered fine-grained sedimentary rocks in Yellowknife Bay, Gale crater, Mars that are inferred to represent an ancient lake environment. Analysis found the environment would have been habitable by microorganisms, with a neutral pH, low salinity, and variable redox states of iron and sulfur. Key biogenic elements like carbon, hydrogen, oxygen, sulfur, nitrogen and phosphorus were detected, suggesting the environment could have supported a Martian biosphere based on chemolithoautotrophy. The habitable conditions were likely present for hundreds to tens of thousands of years. These results highlight the potential for fluvial-lacustrine environments on Mars after the Noachian period to
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
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 document discusses soft rocks in Argentina. It begins by defining soft rocks as sedimentary, pyroclastic, chemical sedimentary, and some metamorphic rocks with low to moderate lithification and minerals with Mohs hardness less than 3.5, such as limestone, gypsum, and shale. In Argentina, soft rocks are widespread but have not received much study despite impacts on engineering projects like dams and tunnels. The document reviews various studies of soft rock properties in Argentina, finding strengths typically between 2 and 38 MPa and high deformability. More research is needed to better understand the geomechanics of these weak rocks.
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.
Curiosity at gale_crater_characterization_and_analysis_of_the_rocknest_sand_s...Sérgio Sacani
The Rocknest sand shadow analyzed by the Curiosity rover on Mars was similar to coarse-grained ripples analyzed by previous rovers. It consisted of an upper layer of very coarse sand grains armoring the surface, underlain by finer grains. Analysis found the sand was around 55% crystalline material of basaltic composition and 45% amorphous iron-rich glass. This amorphous component contained the volatiles detected and was similar to soils analyzed at other Mars sites, implying the materials were locally derived from similar basaltic sources globally on Mars.
The x-ray diffraction analysis of soil samples from Rocknest at Gale Crater on Mars revealed:
1) Crystalline components including plagioclase, olivine, augite, pigeonite, and minor amounts of other phases.
2) 27±14% of the soil was amorphous material, likely containing multiple iron-bearing and volatile phases including possibly hisingerite.
3) The crystalline components are similar to martian basalts and meteorites, while the amorphous component is similar to soils on Earth like those on Mauna Kea, Hawaii.
Linne simple lunar mare crater geometry from lro observationsSérgio Sacani
This document analyzes the geometry of Linne crater on the Moon using high-resolution topographic data from LRO. The key findings are:
1) Linne's crater cavity is best described as a truncated cone, not a "bowl" as previously thought, with an inner wall slope of 33 degrees.
2) Linne's continuous ejecta blanket thickness decays with a power law exponent of -3.84, steeper than the typical -2.75 for craters on Earth.
3) When compared to other simple craters on the Moon, Mars, and Earth, Linne's normalized crater shape parameter suggests it represents an archetypal, well-preserved simple mare
The document discusses the Malampaya gas field located offshore the Philippines. It provides details on the geological setting and depositional environment of the field. The Malampaya reservoir consists of Oligocene-Miocene carbonates deposited during the drifting stage in a reef environment along the continental margin. Stratigraphic correlations of well data using diagenetic units revealed heterogeneity in the reservoir porosity and permeability.
1) Gale Crater is a potential landing site for the Mars Science Laboratory rover. It contains a large mound of layered sediment in the crater's center over 5 km thick.
2) Previous studies have proposed various origins for the mound materials, including lacustrine, aeolian, pyroclastic, and spring deposits. However, the exact origin remains uncertain.
3) This study uses high-resolution imagery and spectral data to characterize the geomorphology and stratigraphy of the mound and crater in order to better understand the depositional environment(s) and evaluate hypotheses for the mound's origin.
Constraints on Ceres’ internal structure and evolution from its shape and gra...Sérgio Sacani
Ceres is the largest body in the asteroid belt with a radius of
approximately 470 km. In part due to its large mass, Ceres more closely approaches
hydrostatic equilibrium than major asteroids. Pre-Dawn mission
shape observations of Ceres revealed a shape consistent with a hydrostatic
ellipsoid of revolution. The Dawn spacecraft Framing Camera has been imaging
Ceres since March 2015, which has led to high-resolution shape models
of the dwarf planet, while the gravity field has been globally determined to
a spherical harmonic degree 14 (equivalent to a spatial wavelength of 211 km)
and locally to 18 (a wavelength of 164 km). We use these shape and gravity
models to constrain Ceres’ internal structure. We find a negative correlation
and admittance between topography and gravity at degree 2 and order
2. Low admittances between spherical harmonic degrees 3 and 16 are well
explained by Airy isostatic compensation mechanism. Different models of isostasy
give crustal densities between 1200 and 1400 kg=m3 with our preferred model
This document discusses using laser ablation and laser pressure techniques to deflect asteroids. It involves using solar-pumped laser pulses from spacecraft to ablate and apply pressure to the asteroid's surface, reducing its momentum and pushing it off course. Key points discussed include:
- Laser ablation involves vaporizing surface material with high-power laser pulses, ejecting a plume that applies force opposite the direction of ablation.
- Laser pressure is a secondary force generated from thermal stresses within the ablated layer that pressurizes subsurface layers.
- Spacecraft would use solar arrays to power lasers, either indirectly by first converting sunlight to electricity or directly through solar-pumped lasers.
- Challenges
Multi wavelenth observations and surveys of galaxy clustersJoana Santos
This document provides an overview of galaxy clusters, focusing on their baryonic components (intracluster medium and galaxies) and how they relate to the cluster's physical properties like mass. It discusses that galaxy clusters form hierarchically through gravitational collapse. The intracluster medium, which makes up most of the baryonic mass, emits X-rays and has been heated to temperatures of millions of degrees. The document reviews properties of the intracluster medium like density, temperature, metallicity, and how they can be measured from X-ray spectra. It also discusses upcoming surveys that will advance the study of galaxy clusters.
An almost dark galaxy with the mass of the Small Magellanic CloudSérgio Sacani
This document describes the discovery and characterization of an almost dark galaxy named Nube. Deep imaging with GTC revealed Nube has an extremely low surface brightness of 26.7 mag/arcsec^2 and a stellar mass of 4x10^8 solar masses. Follow-up observations with GBT detected HI emission from Nube, suggesting it is located 107 Mpc away. At this distance, Nube has a large half-mass radius of 6.9 kpc and low effective stellar density, making it the most extended low-surface brightness galaxy found. Its properties are difficult to reproduce in CDM simulations but are consistent with an ultra-light dark matter particle model.
This document describes a model of crater formation on the Moon and terrestrial planets based on the current understanding of the impactor population in the inner Solar System. The model calculates impact rates spatially across planetary surfaces to account for nonuniform cratering. It finds that the lunar cratering rate varies with latitude and longitude, being about 25% lower in some regions and higher in others. The model reconciles measured lunar crater size-frequency distributions with observations of near-Earth objects, assuming the presence of a porous lunar megaregolith affects the size of small craters. It provides revised estimates of the ages of some lunar and planetary geological features based on crater counts and the derived crater chronology.
The colision between_the_milky_way_and_andromedaSérgio Sacani
The document summarizes a simulation of the future collision between the Milky Way and Andromeda galaxies. It finds that given current observational constraints on their distance, velocity, and masses:
1) The Milky Way and Andromeda are likely to collide in a few billion years, within the lifetime of the Sun.
2) During the interaction, there is a chance the Sun could be pulled into an extended tidal tail between the galaxies.
3) Eventually, after the merger is complete, the Sun would most likely be scattered to the outer halo of the merged galaxy at a distance over 30 kpc.
Martian soil as revealed by ground-penetrating radar at the Tianwen-1 landing...Sérgio Sacani
Much of the Martian surface is covered by a weathering layer (regolith or soil) produced
by long-term surface processes such as impact gardening, eolian erosion, water weathering,
and glacial modifications. China’s first Martian mission, Tianwen-1, employed the Mars
Rover Penetrating Radar (RoPeR) to unveil the detailed structure of the regolith layer and
assess its loss tangent. The RoPeR radargram revealed the local regolith layer to be highly
heterogeneous and geologically complex and characterized by structures that resemble partial
or complete crater walls and near-surface impact lenses at a very shallow depth. However,
comparable radar data from the Lunar far side are rather uniform, despite the two surfaces
being geologically contemporary. The close-to-surface crater presented in this study shows
no detectable surface expression, which suggests an accelerated occultation rate for small
craters on the surface of Mars as compared to the rate on the Moon. This is probably due to
the relentless eolian processes on the Martian surface that led to the burial of the crater and
thus shielded it from further erosion. The high loss tangent indicates that the regolith at the
Tianwen-1 landing site is not dominated by water ice.
well logging project report_ongc project studentknigh7
This dissertation report discusses characterizing oil and gas reservoirs using open hole wireline logging tools and techniques. It provides background on reservoir properties that can be measured using logs like resistivity, porosity, and saturation. It also describes the various electrical, radioactive, sonic, and other open hole wireline logging tools and their measurement principles.
1) Barnard 68 is considered a stable dense molecular cloud core, but observations indicate it should be gravitationally unstable and collapsing.
2) The authors argue Barnard 68 is experiencing a collision with another small core that will trigger its gravitational collapse within the next 200,000 years, forming a low-mass star.
3) Such core mergers may play an important role in triggering star formation and shaping properties of molecular cores and the stellar initial mass function.
Scientists have analyzed data from HED meteorites, which are believed to originate from asteroid 4 Vesta, to help interpret upcoming data from NASA's Dawn spacecraft about Vesta's composition. A mixing model based on the three main rock types of HED meteorites allows researchers to estimate abundances of major and minor elements on Vesta's surface that will be detected by Dawn's GRaND instrument. This integrated approach combining laboratory analysis of meteorite samples and remote sensing from Dawn will provide valuable information about Vesta's igneous history and differentiation.
This document presents the results of a study of 32 Bok globules, which are small, isolated molecular clouds that often contain young stellar objects. Millimeter and submillimeter continuum images were used to detect dust emission from star-forming cores within the globules. These data, along with infrared images and spectral energy distributions, were analyzed to determine the physical properties and evolutionary stages of the embedded sources. Submillimeter dust emission was detected in 26 globules, and the analysis identified 9 starless cores, 9 Class 0 protostars, and 12 Class I young stellar objects. The study found evidence that at least two-thirds of the globules studied were forming multiple stars within distances of 1,000-50,000 AU of each
Exploring the nature and synchronicity of early cluster formation in the Larg...Sérgio Sacani
We analyse Hubble Space Telescope observations of six globular clusters in the Large Magel- lanic Cloud (LMC) from programme GO-14164 in Cycle 23. These are the deepest available observations of the LMC globular cluster population; their uniformity facilitates a precise comparison with globular clusters in the Milky Way. Measuring the magnitude of the main- sequence turn-off point relative to template Galactic globular clusters allows the relative ages of the clusters to be determined with a mean precision of 8.4 per cent, and down to 6 per cent for individual objects. We find that the mean age of our LMC cluster ensemble is identical to the mean age of the oldest metal-poor clusters in the Milky Way halo to 0.2 ± 0.4 Gyr. This provides the most sensitive test to date of the synchronicity of the earliest epoch of globular cluster formation in two independent galaxies. Horizontal branch magnitudes and subdwarf fitting to the main sequence allow us to determine distance estimates for each cluster and examine their geometric distribution in the LMC. Using two different methods, we find an average distance to the LMC of 18.52 ± 0.05.
Evidence for water_ice_near_mercury_north_pole_from_messenger _neutron_spectr...Sérgio Sacani
MESSENGER neutron spectrometer measurements show evidence for water ice near Mercury's north pole. Analysis of fast and epithermal neutron fluxes found a 1.1% decrease in fast neutrons and a 2.4% decrease in epithermal neutrons near the north pole compared to lower latitudes. This signal is consistent with a hydrogen-rich layer more than tens of centimeters thick beneath a surficial layer less than 25% water-equivalent hydrogen that is around 10-20 centimeters thick. The buried hydrogen-rich layer appears to be nearly pure water ice, and the total mass of water ice at Mercury's poles is estimated to be between 2×10^16 to 10^18 grams.
This document summarizes the Regolith & Environment Science, and Oxygen & Lunar Volatile Extraction (RESOLVE) mission architecture for prospecting and utilizing lunar resources. Key aspects include:
The RESOLVE rover payload will conduct a 10-day surface mission at the Cabeus crater near the lunar south pole in May 2016. The payload will acquire samples up to 1m deep and characterize volatiles and perform ISRU demonstrations to extract oxygen.
A solar-powered rover was selected as the architecture to survive a long mission, range far from the landing site, and have the lowest risk. The 243kg rover will survey 3,000m powered by a 250W solar array and 3,
Different Martian Crustal Seismic Velocities across the Dichotomy Boundary fr...Sérgio Sacani
Article This article is protected by copyright. All rights reserved.
Abstract
We have observed both minor-arc (R1) and major-arc (R2) Rayleigh waves for the largest marsquake (magnitude
of 4.7 ± 0.2) ever recorded. Along the R1 path (in the lowlands), inversion results show that a simple, two-layer
model with an interface located at 21 - 29 km and an upper crustal shear-wave velocity of 3.05 - 3.17 km/s can fit the
group velocity measurements. Along the R2 path, observations can be explained by upper crustal thickness models
constrained from gravity data and upper crustal shear-wave velocities of 2.61 - 3.27 km/s and 3.28 - 3.52 km/s in the
lowlands and highlands, respectively. The shear-wave velocity being faster in the highlands than in the lowlands
indicates the possible existence of sedimentary rocks, and relatively higher porosity in the lowlands.
A rock composition_for_earth_sized_exoplanetsSérgio Sacani
1) Researchers measured the mass of Kepler-78b, an Earth-sized exoplanet orbiting its host star every 8.5 hours, to be 1.69 ± 0.41 M⊕ using Doppler spectroscopy of the star's radial velocity variations.
2) Given the planet's radius of 1.20 ± 0.09 R⊕, its mean density of 5.3 ± 1.8 g/cm3 is similar to Earth's, suggesting a rocky composition of iron and rock.
3) Kepler-78b is the smallest exoplanet yet characterized with both an accurate mass and radius measurement, extending measurements of planetary composition into the size range of Earth and Venus.
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.
Curiosity at gale_crater_characterization_and_analysis_of_the_rocknest_sand_s...Sérgio Sacani
The Rocknest sand shadow analyzed by the Curiosity rover on Mars was similar to coarse-grained ripples analyzed by previous rovers. It consisted of an upper layer of very coarse sand grains armoring the surface, underlain by finer grains. Analysis found the sand was around 55% crystalline material of basaltic composition and 45% amorphous iron-rich glass. This amorphous component contained the volatiles detected and was similar to soils analyzed at other Mars sites, implying the materials were locally derived from similar basaltic sources globally on Mars.
The x-ray diffraction analysis of soil samples from Rocknest at Gale Crater on Mars revealed:
1) Crystalline components including plagioclase, olivine, augite, pigeonite, and minor amounts of other phases.
2) 27±14% of the soil was amorphous material, likely containing multiple iron-bearing and volatile phases including possibly hisingerite.
3) The crystalline components are similar to martian basalts and meteorites, while the amorphous component is similar to soils on Earth like those on Mauna Kea, Hawaii.
Linne simple lunar mare crater geometry from lro observationsSérgio Sacani
This document analyzes the geometry of Linne crater on the Moon using high-resolution topographic data from LRO. The key findings are:
1) Linne's crater cavity is best described as a truncated cone, not a "bowl" as previously thought, with an inner wall slope of 33 degrees.
2) Linne's continuous ejecta blanket thickness decays with a power law exponent of -3.84, steeper than the typical -2.75 for craters on Earth.
3) When compared to other simple craters on the Moon, Mars, and Earth, Linne's normalized crater shape parameter suggests it represents an archetypal, well-preserved simple mare
The document discusses the Malampaya gas field located offshore the Philippines. It provides details on the geological setting and depositional environment of the field. The Malampaya reservoir consists of Oligocene-Miocene carbonates deposited during the drifting stage in a reef environment along the continental margin. Stratigraphic correlations of well data using diagenetic units revealed heterogeneity in the reservoir porosity and permeability.
1) Gale Crater is a potential landing site for the Mars Science Laboratory rover. It contains a large mound of layered sediment in the crater's center over 5 km thick.
2) Previous studies have proposed various origins for the mound materials, including lacustrine, aeolian, pyroclastic, and spring deposits. However, the exact origin remains uncertain.
3) This study uses high-resolution imagery and spectral data to characterize the geomorphology and stratigraphy of the mound and crater in order to better understand the depositional environment(s) and evaluate hypotheses for the mound's origin.
Constraints on Ceres’ internal structure and evolution from its shape and gra...Sérgio Sacani
Ceres is the largest body in the asteroid belt with a radius of
approximately 470 km. In part due to its large mass, Ceres more closely approaches
hydrostatic equilibrium than major asteroids. Pre-Dawn mission
shape observations of Ceres revealed a shape consistent with a hydrostatic
ellipsoid of revolution. The Dawn spacecraft Framing Camera has been imaging
Ceres since March 2015, which has led to high-resolution shape models
of the dwarf planet, while the gravity field has been globally determined to
a spherical harmonic degree 14 (equivalent to a spatial wavelength of 211 km)
and locally to 18 (a wavelength of 164 km). We use these shape and gravity
models to constrain Ceres’ internal structure. We find a negative correlation
and admittance between topography and gravity at degree 2 and order
2. Low admittances between spherical harmonic degrees 3 and 16 are well
explained by Airy isostatic compensation mechanism. Different models of isostasy
give crustal densities between 1200 and 1400 kg=m3 with our preferred model
Constraints on Ceres’ internal structure and evolution from its shape and gra...
Similar to The effects of_the_target_material_properties_and layering_on_the_crater_chronology_the_case_of raditladi_and_rachmaninoff_basins_on_mercury
This document discusses using laser ablation and laser pressure techniques to deflect asteroids. It involves using solar-pumped laser pulses from spacecraft to ablate and apply pressure to the asteroid's surface, reducing its momentum and pushing it off course. Key points discussed include:
- Laser ablation involves vaporizing surface material with high-power laser pulses, ejecting a plume that applies force opposite the direction of ablation.
- Laser pressure is a secondary force generated from thermal stresses within the ablated layer that pressurizes subsurface layers.
- Spacecraft would use solar arrays to power lasers, either indirectly by first converting sunlight to electricity or directly through solar-pumped lasers.
- Challenges
Multi wavelenth observations and surveys of galaxy clustersJoana Santos
This document provides an overview of galaxy clusters, focusing on their baryonic components (intracluster medium and galaxies) and how they relate to the cluster's physical properties like mass. It discusses that galaxy clusters form hierarchically through gravitational collapse. The intracluster medium, which makes up most of the baryonic mass, emits X-rays and has been heated to temperatures of millions of degrees. The document reviews properties of the intracluster medium like density, temperature, metallicity, and how they can be measured from X-ray spectra. It also discusses upcoming surveys that will advance the study of galaxy clusters.
An almost dark galaxy with the mass of the Small Magellanic CloudSérgio Sacani
This document describes the discovery and characterization of an almost dark galaxy named Nube. Deep imaging with GTC revealed Nube has an extremely low surface brightness of 26.7 mag/arcsec^2 and a stellar mass of 4x10^8 solar masses. Follow-up observations with GBT detected HI emission from Nube, suggesting it is located 107 Mpc away. At this distance, Nube has a large half-mass radius of 6.9 kpc and low effective stellar density, making it the most extended low-surface brightness galaxy found. Its properties are difficult to reproduce in CDM simulations but are consistent with an ultra-light dark matter particle model.
This document describes a model of crater formation on the Moon and terrestrial planets based on the current understanding of the impactor population in the inner Solar System. The model calculates impact rates spatially across planetary surfaces to account for nonuniform cratering. It finds that the lunar cratering rate varies with latitude and longitude, being about 25% lower in some regions and higher in others. The model reconciles measured lunar crater size-frequency distributions with observations of near-Earth objects, assuming the presence of a porous lunar megaregolith affects the size of small craters. It provides revised estimates of the ages of some lunar and planetary geological features based on crater counts and the derived crater chronology.
The colision between_the_milky_way_and_andromedaSérgio Sacani
The document summarizes a simulation of the future collision between the Milky Way and Andromeda galaxies. It finds that given current observational constraints on their distance, velocity, and masses:
1) The Milky Way and Andromeda are likely to collide in a few billion years, within the lifetime of the Sun.
2) During the interaction, there is a chance the Sun could be pulled into an extended tidal tail between the galaxies.
3) Eventually, after the merger is complete, the Sun would most likely be scattered to the outer halo of the merged galaxy at a distance over 30 kpc.
Martian soil as revealed by ground-penetrating radar at the Tianwen-1 landing...Sérgio Sacani
Much of the Martian surface is covered by a weathering layer (regolith or soil) produced
by long-term surface processes such as impact gardening, eolian erosion, water weathering,
and glacial modifications. China’s first Martian mission, Tianwen-1, employed the Mars
Rover Penetrating Radar (RoPeR) to unveil the detailed structure of the regolith layer and
assess its loss tangent. The RoPeR radargram revealed the local regolith layer to be highly
heterogeneous and geologically complex and characterized by structures that resemble partial
or complete crater walls and near-surface impact lenses at a very shallow depth. However,
comparable radar data from the Lunar far side are rather uniform, despite the two surfaces
being geologically contemporary. The close-to-surface crater presented in this study shows
no detectable surface expression, which suggests an accelerated occultation rate for small
craters on the surface of Mars as compared to the rate on the Moon. This is probably due to
the relentless eolian processes on the Martian surface that led to the burial of the crater and
thus shielded it from further erosion. The high loss tangent indicates that the regolith at the
Tianwen-1 landing site is not dominated by water ice.
well logging project report_ongc project studentknigh7
This dissertation report discusses characterizing oil and gas reservoirs using open hole wireline logging tools and techniques. It provides background on reservoir properties that can be measured using logs like resistivity, porosity, and saturation. It also describes the various electrical, radioactive, sonic, and other open hole wireline logging tools and their measurement principles.
1) Barnard 68 is considered a stable dense molecular cloud core, but observations indicate it should be gravitationally unstable and collapsing.
2) The authors argue Barnard 68 is experiencing a collision with another small core that will trigger its gravitational collapse within the next 200,000 years, forming a low-mass star.
3) Such core mergers may play an important role in triggering star formation and shaping properties of molecular cores and the stellar initial mass function.
Scientists have analyzed data from HED meteorites, which are believed to originate from asteroid 4 Vesta, to help interpret upcoming data from NASA's Dawn spacecraft about Vesta's composition. A mixing model based on the three main rock types of HED meteorites allows researchers to estimate abundances of major and minor elements on Vesta's surface that will be detected by Dawn's GRaND instrument. This integrated approach combining laboratory analysis of meteorite samples and remote sensing from Dawn will provide valuable information about Vesta's igneous history and differentiation.
This document presents the results of a study of 32 Bok globules, which are small, isolated molecular clouds that often contain young stellar objects. Millimeter and submillimeter continuum images were used to detect dust emission from star-forming cores within the globules. These data, along with infrared images and spectral energy distributions, were analyzed to determine the physical properties and evolutionary stages of the embedded sources. Submillimeter dust emission was detected in 26 globules, and the analysis identified 9 starless cores, 9 Class 0 protostars, and 12 Class I young stellar objects. The study found evidence that at least two-thirds of the globules studied were forming multiple stars within distances of 1,000-50,000 AU of each
Exploring the nature and synchronicity of early cluster formation in the Larg...Sérgio Sacani
We analyse Hubble Space Telescope observations of six globular clusters in the Large Magel- lanic Cloud (LMC) from programme GO-14164 in Cycle 23. These are the deepest available observations of the LMC globular cluster population; their uniformity facilitates a precise comparison with globular clusters in the Milky Way. Measuring the magnitude of the main- sequence turn-off point relative to template Galactic globular clusters allows the relative ages of the clusters to be determined with a mean precision of 8.4 per cent, and down to 6 per cent for individual objects. We find that the mean age of our LMC cluster ensemble is identical to the mean age of the oldest metal-poor clusters in the Milky Way halo to 0.2 ± 0.4 Gyr. This provides the most sensitive test to date of the synchronicity of the earliest epoch of globular cluster formation in two independent galaxies. Horizontal branch magnitudes and subdwarf fitting to the main sequence allow us to determine distance estimates for each cluster and examine their geometric distribution in the LMC. Using two different methods, we find an average distance to the LMC of 18.52 ± 0.05.
Evidence for water_ice_near_mercury_north_pole_from_messenger _neutron_spectr...Sérgio Sacani
MESSENGER neutron spectrometer measurements show evidence for water ice near Mercury's north pole. Analysis of fast and epithermal neutron fluxes found a 1.1% decrease in fast neutrons and a 2.4% decrease in epithermal neutrons near the north pole compared to lower latitudes. This signal is consistent with a hydrogen-rich layer more than tens of centimeters thick beneath a surficial layer less than 25% water-equivalent hydrogen that is around 10-20 centimeters thick. The buried hydrogen-rich layer appears to be nearly pure water ice, and the total mass of water ice at Mercury's poles is estimated to be between 2×10^16 to 10^18 grams.
This document summarizes the Regolith & Environment Science, and Oxygen & Lunar Volatile Extraction (RESOLVE) mission architecture for prospecting and utilizing lunar resources. Key aspects include:
The RESOLVE rover payload will conduct a 10-day surface mission at the Cabeus crater near the lunar south pole in May 2016. The payload will acquire samples up to 1m deep and characterize volatiles and perform ISRU demonstrations to extract oxygen.
A solar-powered rover was selected as the architecture to survive a long mission, range far from the landing site, and have the lowest risk. The 243kg rover will survey 3,000m powered by a 250W solar array and 3,
Different Martian Crustal Seismic Velocities across the Dichotomy Boundary fr...Sérgio Sacani
Article This article is protected by copyright. All rights reserved.
Abstract
We have observed both minor-arc (R1) and major-arc (R2) Rayleigh waves for the largest marsquake (magnitude
of 4.7 ± 0.2) ever recorded. Along the R1 path (in the lowlands), inversion results show that a simple, two-layer
model with an interface located at 21 - 29 km and an upper crustal shear-wave velocity of 3.05 - 3.17 km/s can fit the
group velocity measurements. Along the R2 path, observations can be explained by upper crustal thickness models
constrained from gravity data and upper crustal shear-wave velocities of 2.61 - 3.27 km/s and 3.28 - 3.52 km/s in the
lowlands and highlands, respectively. The shear-wave velocity being faster in the highlands than in the lowlands
indicates the possible existence of sedimentary rocks, and relatively higher porosity in the lowlands.
A rock composition_for_earth_sized_exoplanetsSérgio Sacani
1) Researchers measured the mass of Kepler-78b, an Earth-sized exoplanet orbiting its host star every 8.5 hours, to be 1.69 ± 0.41 M⊕ using Doppler spectroscopy of the star's radial velocity variations.
2) Given the planet's radius of 1.20 ± 0.09 R⊕, its mean density of 5.3 ± 1.8 g/cm3 is similar to Earth's, suggesting a rocky composition of iron and rock.
3) Kepler-78b is the smallest exoplanet yet characterized with both an accurate mass and radius measurement, extending measurements of planetary composition into the size range of Earth and Venus.
A recently formed ocean inside Saturn’s moon MimasSérgio Sacani
Moons potentially harbouring a global ocean are tending to become relatively common objects in the Solar System1. The presence of these long-lived global oceans is generally betrayed by surface modification owing to internal dynamics2. Hence, Mimas would be the most unlikely place to look for the presence of a global ocean3. Here, from detailed analysis of Mimas’s orbital motion based on Cassini data, with a particular focus on Mimas’s periapsis drift, we show that its heavily cratered icy shell hides a global ocean, at a depth of 20–30 kilometres. Eccentricity damping implies that the ocean is likely to be less than 25 million years old and still evolving. Our simulations show that the ocean–ice interface reached a depth of less than 30 kilometres only recently (less than 2–3 million years ago), a time span too short for signs of activity at Mimas’s surface to have appeared.
A giant thin stellar stream in the Coma Galaxy ClusterSérgio Sacani
The study of dynamically cold stellar streams reveals information about the gravitational potential where they reside and provides
important constraints on the properties of dark matter. However, the intrinsic faintness of these streams makes their detection beyond
Local environments highly challenging. Here, we report the detection of an extremely faint stellar stream (µg,max = 29.5 mag arcsec−2
)
with an extraordinarily coherent and thin morphology in the Coma Galaxy Cluster. This Giant Coma Stream spans ∼510 kpc in length
and appears as a free-floating structure located at a projected distance of 0.8 Mpc from the center of Coma. We do not identify any
potential galaxy remnant or core, and the stream structure appears featureless in our data. We interpret the Giant Coma Stream as
being a recently accreted, tidally disrupting passive dwarf. Using the Illustris-TNG50 simulation, we identify a case with similar
characteristics, showing that, although rare, these types of streams are predicted to exist in Λ-CDM. Our work unveils the presence
of free-floating, extremely faint and thin stellar streams in galaxy clusters, widening the environmental context in which these objects
are found ahead of their promising future application in the study of the properties of dark matter.
This document summarizes a study that estimates the dynamical surface mass density between 1.5 and 4 kpc from the Galactic plane using kinematics of thick disk stars. The authors derive an exact analytical expression for the surface density based on assumptions about the stellar population and Galactic potential. Their expression matches expectations of visible mass alone, with no evidence for additional dark matter required. They extrapolate a local dark matter density of 0±1 mM⊙ pc−3, excluding all current spherical dark matter halo models at over 4σ confidence. Only a highly prolate dark matter halo could potentially reconcile the observations with models, but this is unlikely according to ΛCDM.
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.
Science with small telescopes - exoplanetsguest8aa6ebb
The search for extrasolar planets has become one of the most attractive problems in modern astrophysics. The biggest observatories in the world are involved in this task as well as little amateur instruments. There is also a huge variety of astronomical methods used for their investigation. Here I present the projects for searching for exoplanets by transit method and our observations of the planet WASP-2b. We observed a transit on 3/4 August 2008 with a 354 mm Schmidt-Cassegrain Celestron telescope and CCD SBIG STL 11000M camera. By precise photometry made using MaximDL software we obtained the light curve of the star system. Decrease of brightness by 0.02m is detected. Analyzing our data we estimate the radius of the planet and inclination of its orbit. Our results are in good correlation with the published information in literature.
Similar to The effects of_the_target_material_properties_and layering_on_the_crater_chronology_the_case_of raditladi_and_rachmaninoff_basins_on_mercury (20)
The binding of cosmological structures by massless topological defectsSérgio Sacani
Assuming spherical symmetry and weak field, it is shown that if one solves the Poisson equation or the Einstein field
equations sourced by a topological defect, i.e. a singularity of a very specific form, the result is a localized gravitational
field capable of driving flat rotation (i.e. Keplerian circular orbits at a constant speed for all radii) of test masses on a thin
spherical shell without any underlying mass. Moreover, a large-scale structure which exploits this solution by assembling
concentrically a number of such topological defects can establish a flat stellar or galactic rotation curve, and can also deflect
light in the same manner as an equipotential (isothermal) sphere. Thus, the need for dark matter or modified gravity theory is
mitigated, at least in part.
EWOCS-I: The catalog of X-ray sources in Westerlund 1 from the Extended Weste...Sérgio Sacani
Context. With a mass exceeding several 104 M⊙ and a rich and dense population of massive stars, supermassive young star clusters
represent the most massive star-forming environment that is dominated by the feedback from massive stars and gravitational interactions
among stars.
Aims. In this paper we present the Extended Westerlund 1 and 2 Open Clusters Survey (EWOCS) project, which aims to investigate
the influence of the starburst environment on the formation of stars and planets, and on the evolution of both low and high mass stars.
The primary targets of this project are Westerlund 1 and 2, the closest supermassive star clusters to the Sun.
Methods. The project is based primarily on recent observations conducted with the Chandra and JWST observatories. Specifically,
the Chandra survey of Westerlund 1 consists of 36 new ACIS-I observations, nearly co-pointed, for a total exposure time of 1 Msec.
Additionally, we included 8 archival Chandra/ACIS-S observations. This paper presents the resulting catalog of X-ray sources within
and around Westerlund 1. Sources were detected by combining various existing methods, and photon extraction and source validation
were carried out using the ACIS-Extract software.
Results. The EWOCS X-ray catalog comprises 5963 validated sources out of the 9420 initially provided to ACIS-Extract, reaching a
photon flux threshold of approximately 2 × 10−8 photons cm−2
s
−1
. The X-ray sources exhibit a highly concentrated spatial distribution,
with 1075 sources located within the central 1 arcmin. We have successfully detected X-ray emissions from 126 out of the 166 known
massive stars of the cluster, and we have collected over 71 000 photons from the magnetar CXO J164710.20-455217.
The debris of the ‘last major merger’ is dynamically youngSérgio Sacani
The Milky Way’s (MW) inner stellar halo contains an [Fe/H]-rich component with highly eccentric orbits, often referred to as the
‘last major merger.’ Hypotheses for the origin of this component include Gaia-Sausage/Enceladus (GSE), where the progenitor
collided with the MW proto-disc 8–11 Gyr ago, and the Virgo Radial Merger (VRM), where the progenitor collided with the
MW disc within the last 3 Gyr. These two scenarios make different predictions about observable structure in local phase space,
because the morphology of debris depends on how long it has had to phase mix. The recently identified phase-space folds in Gaia
DR3 have positive caustic velocities, making them fundamentally different than the phase-mixed chevrons found in simulations
at late times. Roughly 20 per cent of the stars in the prograde local stellar halo are associated with the observed caustics. Based
on a simple phase-mixing model, the observed number of caustics are consistent with a merger that occurred 1–2 Gyr ago.
We also compare the observed phase-space distribution to FIRE-2 Latte simulations of GSE-like mergers, using a quantitative
measurement of phase mixing (2D causticality). The observed local phase-space distribution best matches the simulated data
1–2 Gyr after collision, and certainly not later than 3 Gyr. This is further evidence that the progenitor of the ‘last major merger’
did not collide with the MW proto-disc at early times, as is thought for the GSE, but instead collided with the MW disc within
the last few Gyr, consistent with the body of work surrounding the VRM.
Observation of Io’s Resurfacing via Plume Deposition Using Ground-based Adapt...Sérgio Sacani
Since volcanic activity was first discovered on Io from Voyager images in 1979, changes
on Io’s surface have been monitored from both spacecraft and ground-based telescopes.
Here, we present the highest spatial resolution images of Io ever obtained from a groundbased telescope. These images, acquired by the SHARK-VIS instrument on the Large
Binocular Telescope, show evidence of a major resurfacing event on Io’s trailing hemisphere. When compared to the most recent spacecraft images, the SHARK-VIS images
show that a plume deposit from a powerful eruption at Pillan Patera has covered part
of the long-lived Pele plume deposit. Although this type of resurfacing event may be common on Io, few have been detected due to the rarity of spacecraft visits and the previously low spatial resolution available from Earth-based telescopes. The SHARK-VIS instrument ushers in a new era of high resolution imaging of Io’s surface using adaptive
optics at visible wavelengths.
Earliest Galaxies in the JADES Origins Field: Luminosity Function and Cosmic ...Sérgio Sacani
We characterize the earliest galaxy population in the JADES Origins Field (JOF), the deepest
imaging field observed with JWST. We make use of the ancillary Hubble optical images (5 filters
spanning 0.4−0.9µm) and novel JWST images with 14 filters spanning 0.8−5µm, including 7 mediumband filters, and reaching total exposure times of up to 46 hours per filter. We combine all our data
at > 2.3µm to construct an ultradeep image, reaching as deep as ≈ 31.4 AB mag in the stack and
30.3-31.0 AB mag (5σ, r = 0.1” circular aperture) in individual filters. We measure photometric
redshifts and use robust selection criteria to identify a sample of eight galaxy candidates at redshifts
z = 11.5 − 15. These objects show compact half-light radii of R1/2 ∼ 50 − 200pc, stellar masses of
M⋆ ∼ 107−108M⊙, and star-formation rates of SFR ∼ 0.1−1 M⊙ yr−1
. Our search finds no candidates
at 15 < z < 20, placing upper limits at these redshifts. We develop a forward modeling approach to
infer the properties of the evolving luminosity function without binning in redshift or luminosity that
marginalizes over the photometric redshift uncertainty of our candidate galaxies and incorporates the
impact of non-detections. We find a z = 12 luminosity function in good agreement with prior results,
and that the luminosity function normalization and UV luminosity density decline by a factor of ∼ 2.5
from z = 12 to z = 14. We discuss the possible implications of our results in the context of theoretical
models for evolution of the dark matter halo mass function.
THE IMPORTANCE OF MARTIAN ATMOSPHERE SAMPLE RETURN.Sérgio Sacani
The return of a sample of near-surface atmosphere from Mars would facilitate answers to several first-order science questions surrounding the formation and evolution of the planet. One of the important aspects of terrestrial planet formation in general is the role that primary atmospheres played in influencing the chemistry and structure of the planets and their antecedents. Studies of the martian atmosphere can be used to investigate the role of a primary atmosphere in its history. Atmosphere samples would also inform our understanding of the near-surface chemistry of the planet, and ultimately the prospects for life. High-precision isotopic analyses of constituent gases are needed to address these questions, requiring that the analyses are made on returned samples rather than in situ.
Multi-source connectivity as the driver of solar wind variability in the heli...Sérgio Sacani
The ambient solar wind that flls the heliosphere originates from multiple
sources in the solar corona and is highly structured. It is often described
as high-speed, relatively homogeneous, plasma streams from coronal
holes and slow-speed, highly variable, streams whose source regions are
under debate. A key goal of ESA/NASA’s Solar Orbiter mission is to identify
solar wind sources and understand what drives the complexity seen in the
heliosphere. By combining magnetic feld modelling and spectroscopic
techniques with high-resolution observations and measurements, we show
that the solar wind variability detected in situ by Solar Orbiter in March
2022 is driven by spatio-temporal changes in the magnetic connectivity to
multiple sources in the solar atmosphere. The magnetic feld footpoints
connected to the spacecraft moved from the boundaries of a coronal hole
to one active region (12961) and then across to another region (12957). This
is refected in the in situ measurements, which show the transition from fast
to highly Alfvénic then to slow solar wind that is disrupted by the arrival of
a coronal mass ejection. Our results describe solar wind variability at 0.5 au
but are applicable to near-Earth observatories.
Gliese 12 b: A Temperate Earth-sized Planet at 12 pc Ideal for Atmospheric Tr...Sérgio Sacani
Recent discoveries of Earth-sized planets transiting nearby M dwarfs have made it possible to characterize the
atmospheres of terrestrial planets via follow-up spectroscopic observations. However, the number of such planets
receiving low insolation is still small, limiting our ability to understand the diversity of the atmospheric
composition and climates of temperate terrestrial planets. We report the discovery of an Earth-sized planet
transiting the nearby (12 pc) inactive M3.0 dwarf Gliese 12 (TOI-6251) with an orbital period (Porb) of 12.76 days.
The planet, Gliese 12 b, was initially identified as a candidate with an ambiguous Porb from TESS data. We
confirmed the transit signal and Porb using ground-based photometry with MuSCAT2 and MuSCAT3, and
validated the planetary nature of the signal using high-resolution images from Gemini/NIRI and Keck/NIRC2 as
well as radial velocity (RV) measurements from the InfraRed Doppler instrument on the Subaru 8.2 m telescope
and from CARMENES on the CAHA 3.5 m telescope. X-ray observations with XMM-Newton showed the host
star is inactive, with an X-ray-to-bolometric luminosity ratio of log 5.7 L L X bol » - . Joint analysis of the light
curves and RV measurements revealed that Gliese 12 b has a radius of 0.96 ± 0.05 R⊕,a3σ mass upper limit of
3.9 M⊕, and an equilibrium temperature of 315 ± 6 K assuming zero albedo. The transmission spectroscopy metric
(TSM) value of Gliese 12 b is close to the TSM values of the TRAPPIST-1 planets, adding Gliese 12 b to the small
list of potentially terrestrial, temperate planets amenable to atmospheric characterization with JWST.
Gliese 12 b, a temperate Earth-sized planet at 12 parsecs discovered with TES...Sérgio Sacani
We report on the discovery of Gliese 12 b, the nearest transiting temperate, Earth-sized planet found to date. Gliese 12 is a
bright (V = 12.6 mag, K = 7.8 mag) metal-poor M4V star only 12.162 ± 0.005 pc away from the Solar system with one of the
lowest stellar activity levels known for M-dwarfs. A planet candidate was detected by TESS based on only 3 transits in sectors
42, 43, and 57, with an ambiguity in the orbital period due to observational gaps. We performed follow-up transit observations
with CHEOPS and ground-based photometry with MINERVA-Australis, SPECULOOS, and Purple Mountain Observatory,
as well as further TESS observations in sector 70. We statistically validate Gliese 12 b as a planet with an orbital period of
12.76144 ± 0.00006 d and a radius of 1.0 ± 0.1 R⊕, resulting in an equilibrium temperature of ∼315 K. Gliese 12 b has excellent
future prospects for precise mass measurement, which may inform how planetary internal structure is affected by the stellar
compositional environment. Gliese 12 b also represents one of the best targets to study whether Earth-like planets orbiting cool
stars can retain their atmospheres, a crucial step to advance our understanding of habitability on Earth and across the galaxy.
The importance of continents, oceans and plate tectonics for the evolution of...Sérgio Sacani
Within the uncertainties of involved astronomical and biological parameters, the Drake Equation
typically predicts that there should be many exoplanets in our galaxy hosting active, communicative
civilizations (ACCs). These optimistic calculations are however not supported by evidence, which is
often referred to as the Fermi Paradox. Here, we elaborate on this long-standing enigma by showing
the importance of planetary tectonic style for biological evolution. We summarize growing evidence
that a prolonged transition from Mesoproterozoic active single lid tectonics (1.6 to 1.0 Ga) to modern
plate tectonics occurred in the Neoproterozoic Era (1.0 to 0.541 Ga), which dramatically accelerated
emergence and evolution of complex species. We further suggest that both continents and oceans
are required for ACCs because early evolution of simple life must happen in water but late evolution
of advanced life capable of creating technology must happen on land. We resolve the Fermi Paradox
(1) by adding two additional terms to the Drake Equation: foc
(the fraction of habitable exoplanets
with significant continents and oceans) and fpt
(the fraction of habitable exoplanets with significant
continents and oceans that have had plate tectonics operating for at least 0.5 Ga); and (2) by
demonstrating that the product of foc
and fpt
is very small (< 0.00003–0.002). We propose that the lack
of evidence for ACCs reflects the scarcity of long-lived plate tectonics and/or continents and oceans on
exoplanets with primitive life.
A Giant Impact Origin for the First Subduction on EarthSérgio Sacani
Hadean zircons provide a potential record of Earth's earliest subduction 4.3 billion years ago. Itremains enigmatic how subduction could be initiated so soon after the presumably Moon‐forming giant impact(MGI). Earlier studies found an increase in Earth's core‐mantle boundary (CMB) temperature due to theaccumulation of the impactor's core, and our recent work shows Earth's lower mantle remains largely solid, withsome of the impactor's mantle potentially surviving as the large low‐shear velocity provinces (LLSVPs). Here,we show that a hot post‐impact CMB drives the initiation of strong mantle plumes that can induce subductioninitiation ∼200 Myr after the MGI. 2D and 3D thermomechanical computations show that a high CMBtemperature is the primary factor triggering early subduction, with enrichment of heat‐producing elements inLLSVPs as another potential factor. The models link the earliest subduction to the MGI with implications forunderstanding the diverse tectonic regimes of rocky planets.
Climate extremes likely to drive land mammal extinction during next supercont...Sérgio Sacani
Mammals have dominated Earth for approximately 55 Myr thanks to their
adaptations and resilience to warming and cooling during the Cenozoic. All
life will eventually perish in a runaway greenhouse once absorbed solar
radiation exceeds the emission of thermal radiation in several billions of
years. However, conditions rendering the Earth naturally inhospitable to
mammals may develop sooner because of long-term processes linked to
plate tectonics (short-term perturbations are not considered here). In
~250 Myr, all continents will converge to form Earth’s next supercontinent,
Pangea Ultima. A natural consequence of the creation and decay of Pangea
Ultima will be extremes in pCO2 due to changes in volcanic rifting and
outgassing. Here we show that increased pCO2, solar energy (F⨀;
approximately +2.5% W m−2 greater than today) and continentality (larger
range in temperatures away from the ocean) lead to increasing warming
hostile to mammalian life. We assess their impact on mammalian
physiological limits (dry bulb, wet bulb and Humidex heat stress indicators)
as well as a planetary habitability index. Given mammals’ continued survival,
predicted background pCO2 levels of 410–816 ppm combined with increased
F⨀ will probably lead to a climate tipping point and their mass extinction.
The results also highlight how global landmass configuration, pCO2 and F⨀
play a critical role in planetary habitability.
Constraints on Neutrino Natal Kicks from Black-Hole Binary VFTS 243Sérgio Sacani
The recently reported observation of VFTS 243 is the first example of a massive black-hole binary
system with negligible binary interaction following black-hole formation. The black-hole mass (≈10M⊙)
and near-circular orbit (e ≈ 0.02) of VFTS 243 suggest that the progenitor star experienced complete
collapse, with energy-momentum being lost predominantly through neutrinos. VFTS 243 enables us to
constrain the natal kick and neutrino-emission asymmetry during black-hole formation. At 68% confidence
level, the natal kick velocity (mass decrement) is ≲10 km=s (≲1.0M⊙), with a full probability distribution
that peaks when ≈0.3M⊙ were ejected, presumably in neutrinos, and the black hole experienced a natal
kick of 4 km=s. The neutrino-emission asymmetry is ≲4%, with best fit values of ∼0–0.2%. Such a small
neutrino natal kick accompanying black-hole formation is in agreement with theoretical predictions.
Detectability of Solar Panels as a TechnosignatureSérgio Sacani
In this work, we assess the potential detectability of solar panels made of silicon on an Earth-like
exoplanet as a potential technosignature. Silicon-based photovoltaic cells have high reflectance in the
UV-VIS and in the near-IR, within the wavelength range of a space-based flagship mission concept
like the Habitable Worlds Observatory (HWO). Assuming that only solar energy is used to provide
the 2022 human energy needs with a land cover of ∼ 2.4%, and projecting the future energy demand
assuming various growth-rate scenarios, we assess the detectability with an 8 m HWO-like telescope.
Assuming the most favorable viewing orientation, and focusing on the strong absorption edge in the
ultraviolet-to-visible (0.34 − 0.52 µm), we find that several 100s of hours of observation time is needed
to reach a SNR of 5 for an Earth-like planet around a Sun-like star at 10pc, even with a solar panel
coverage of ∼ 23% land coverage of a future Earth. We discuss the necessity of concepts like Kardeshev
Type I/II civilizations and Dyson spheres, which would aim to harness vast amounts of energy. Even
with much larger populations than today, the total energy use of human civilization would be orders of
magnitude below the threshold for causing direct thermal heating or reaching the scale of a Kardashev
Type I civilization. Any extraterrrestrial civilization that likewise achieves sustainable population
levels may also find a limit on its need to expand, which suggests that a galaxy-spanning civilization
as imagined in the Fermi paradox may not exist.
Jet reorientation in central galaxies of clusters and groups: insights from V...Sérgio Sacani
Recent observations of galaxy clusters and groups with misalignments between their central AGN jets
and X-ray cavities, or with multiple misaligned cavities, have raised concerns about the jet – bubble
connection in cooling cores, and the processes responsible for jet realignment. To investigate the
frequency and causes of such misalignments, we construct a sample of 16 cool core galaxy clusters and
groups. Using VLBA radio data we measure the parsec-scale position angle of the jets, and compare
it with the position angle of the X-ray cavities detected in Chandra data. Using the overall sample
and selected subsets, we consistently find that there is a 30% – 38% chance to find a misalignment
larger than ∆Ψ = 45◦ when observing a cluster/group with a detected jet and at least one cavity. We
determine that projection may account for an apparently large ∆Ψ only in a fraction of objects (∼35%),
and given that gas dynamical disturbances (as sloshing) are found in both aligned and misaligned
systems, we exclude environmental perturbation as the main driver of cavity – jet misalignment.
Moreover, we find that large misalignments (up to ∼ 90◦
) are favored over smaller ones (45◦ ≤ ∆Ψ ≤
70◦
), and that the change in jet direction can occur on timescales between one and a few tens of Myr.
We conclude that misalignments are more likely related to actual reorientation of the jet axis, and we
discuss several engine-based mechanisms that may cause these dramatic changes.
The solar dynamo begins near the surfaceSérgio Sacani
The magnetic dynamo cycle of the Sun features a distinct pattern: a propagating
region of sunspot emergence appears around 30° latitude and vanishes near the
equator every 11 years (ref. 1). Moreover, longitudinal flows called torsional oscillations
closely shadow sunspot migration, undoubtedly sharing a common cause2. Contrary
to theories suggesting deep origins of these phenomena, helioseismology pinpoints
low-latitude torsional oscillations to the outer 5–10% of the Sun, the near-surface
shear layer3,4. Within this zone, inwardly increasing differential rotation coupled with
a poloidal magnetic field strongly implicates the magneto-rotational instability5,6,
prominent in accretion-disk theory and observed in laboratory experiments7.
Together, these two facts prompt the general question: whether the solar dynamo is
possibly a near-surface instability. Here we report strong affirmative evidence in stark
contrast to traditional models8 focusing on the deeper tachocline. Simple analytic
estimates show that the near-surface magneto-rotational instability better explains
the spatiotemporal scales of the torsional oscillations and inferred subsurface
magnetic field amplitudes9. State-of-the-art numerical simulations corroborate these
estimates and reproduce hemispherical magnetic current helicity laws10. The dynamo
resulting from a well-understood near-surface phenomenon improves prospects
for accurate predictions of full magnetic cycles and space weather, affecting the
electromagnetic infrastructure of Earth.
Extensive Pollution of Uranus and Neptune’s Atmospheres by Upsweep of Icy Mat...Sérgio Sacani
In the Nice model of solar system formation, Uranus and Neptune undergo an orbital upheaval,
sweeping through a planetesimal disk. The region of the disk from which material is accreted by
the ice giants during this phase of their evolution has not previously been identified. We perform
direct N-body orbital simulations of the four giant planets to determine the amount and origin of solid
accretion during this orbital upheaval. We find that the ice giants undergo an extreme bombardment
event, with collision rates as much as ∼3 per hour assuming km-sized planetesimals, increasing the
total planet mass by up to ∼0.35%. In all cases, the initially outermost ice giant experiences the
largest total enhancement. We determine that for some plausible planetesimal properties, the resulting
atmospheric enrichment could potentially produce sufficient latent heat to alter the planetary cooling
timescale according to existing models. Our findings suggest that substantial accretion during this
phase of planetary evolution may have been sufficient to impact the atmospheric composition and
thermal evolution of the ice giants, motivating future work on the fate of deposited solid material.
Exomoons & Exorings with the Habitable Worlds Observatory I: On the Detection...Sérgio Sacani
The highest priority recommendation of the Astro2020 Decadal Survey for space-based astronomy
was the construction of an observatory capable of characterizing habitable worlds. In this paper series
we explore the detectability of and interference from exomoons and exorings serendipitously observed
with the proposed Habitable Worlds Observatory (HWO) as it seeks to characterize exoplanets, starting
in this manuscript with Earth-Moon analog mutual events. Unlike transits, which only occur in systems
viewed near edge-on, shadow (i.e., solar eclipse) and lunar eclipse mutual events occur in almost every
star-planet-moon system. The cadence of these events can vary widely from ∼yearly to multiple events
per day, as was the case in our younger Earth-Moon system. Leveraging previous space-based (EPOXI)
lightcurves of a Moon transit and performance predictions from the LUVOIR-B concept, we derive
the detectability of Moon analogs with HWO. We determine that Earth-Moon analogs are detectable
with observation of ∼2-20 mutual events for systems within 10 pc, and larger moons should remain
detectable out to 20 pc. We explore the extent to which exomoon mutual events can mimic planet
features and weather. We find that HWO wavelength coverage in the near-IR, specifically in the 1.4 µm
water band where large moons can outshine their host planet, will aid in differentiating exomoon signals
from exoplanet variability. Finally, we predict that exomoons formed through collision processes akin
to our Moon are more likely to be detected in younger systems, where shorter orbital periods and
favorable geometry enhance the probability and frequency of mutual events.
Emergent ribozyme behaviors in oxychlorine brines indicate a unique niche for...Sérgio Sacani
Mars is a particularly attractive candidate among known astronomical objects
to potentially host life. Results from space exploration missions have provided
insights into Martian geochemistry that indicate oxychlorine species, particularly perchlorate, are ubiquitous features of the Martian geochemical landscape. Perchlorate presents potential obstacles for known forms of life due to
its toxicity. However, it can also provide potential benefits, such as producing
brines by deliquescence, like those thought to exist on present-day Mars. Here
we show perchlorate brines support folding and catalysis of functional RNAs,
while inactivating representative protein enzymes. Additionally, we show
perchlorate and other oxychlorine species enable ribozyme functions,
including homeostasis-like regulatory behavior and ribozyme-catalyzed
chlorination of organic molecules. We suggest nucleic acids are uniquely wellsuited to hypersaline Martian environments. Furthermore, Martian near- or
subsurface oxychlorine brines, and brines found in potential lifeforms, could
provide a unique niche for biomolecular evolution.
Continuum emission from within the plunging region of black hole discsSérgio Sacani
The thermal continuum emission observed from accreting black holes across X-ray bands has the potential to be leveraged as a
powerful probe of the mass and spin of the central black hole. The vast majority of existing ‘continuum fitting’ models neglect
emission sourced at and within the innermost stable circular orbit (ISCO) of the black hole. Numerical simulations, however,
find non-zero emission sourced from these regions. In this work, we extend existing techniques by including the emission
sourced from within the plunging region, utilizing new analytical models that reproduce the properties of numerical accretion
simulations. We show that in general the neglected intra-ISCO emission produces a hot-and-small quasi-blackbody component,
but can also produce a weak power-law tail for more extreme parameter regions. A similar hot-and-small blackbody component
has been added in by hand in an ad hoc manner to previous analyses of X-ray binary spectra. We show that the X-ray spectrum
of MAXI J1820+070 in a soft-state outburst is extremely well described by a full Kerr black hole disc, while conventional
models that neglect intra-ISCO emission are unable to reproduce the data. We believe this represents the first robust detection of
intra-ISCO emission in the literature, and allows additional constraints to be placed on the MAXI J1820 + 070 black hole spin
which must be low a• < 0.5 to allow a detectable intra-ISCO region. Emission from within the ISCO is the dominant emission
component in the MAXI J1820 + 070 spectrum between 6 and 10 keV, highlighting the necessity of including this region. Our
continuum fitting model is made publicly available.
Continuum emission from within the plunging region of black hole discs
The effects of_the_target_material_properties_and layering_on_the_crater_chronology_the_case_of raditladi_and_rachmaninoff_basins_on_mercury
1. The effects of the target material properties and layering on the
crater chronology: the case of Raditladi and Rachmaninoff basins
on Mercury
S. Marchia,∗, M. Massironib , G. Cremonesec, E. Martellatod , L. Giacominib , L. Procktere
arXiv:1105.5272v1 [astro-ph.EP] 25 May 2011
a Departement Cassiop´ e, Universite de Nice - Sophia Antipolis, Observatoire de la Cˆ te d’Azur, CNRS, Nice, France
e o
b Department of Geosciences, Padova University, Italy
c
INAF-Padova, Italy
d Center of Studies and Activities for Space, Padova University, Italy
e Applied Physics Laboratory, Johns Hopkins University, USA
Abstract
In this paper we present a crater age determination of several terrains associated with the Ra-
ditladi and Rachmaninoff basins. These basins were discovered during the first and third MES-
SENGER flybys of Mercury, respectively. One of the most interesting features of both basins is
their relatively fresh appearance. The young age of both basins is confirmed by our analysis on
the basis of age determination via crater chronology. The derived Rachmaninoff and Raditladi
basin model ages are about 3.6 Ga and 1.1 Ga, respectively. Moreover, we also constrain the age
of the smooth plains within the basins’ floors. This analysis shows that Mercury had volcanic
activity until recent time, possibly to about 1 Ga or less. We find that some of the crater size-
frequency distributions investigated suggest the presence of a layered target. Therefore, within
this work we address the importance of considering terrain parameters, as geo-mechanical prop-
erties and layering, into the process of age determination. We also comment on the likelihood of
the availability of impactors able to form basins with the sizes of Rachmaninoff and Raditladi in
relatively recent times.
Keywords: Mercury, Raditladi basin, Rachmaninoff basin, Craters, Age determination
1. Introduction
During MESSENGER’s third flyby of Mercury, a 290-km-diameter peak-ring (double-ring)
impact basin, centered at 27.6◦ N, 57.6◦ E, was discovered and subsequently named Rachmani-
noff. In terms of size and morphology, the Rachmaninoff basin closely resembles the 265-km-
diameter Raditladi peak-ring basin, located at 27◦ N, 119◦ E west of the Caloris basin, that was
discovered during MESSENGER’s first flyby [24]. The image-mosaic of Rachmaninoff and its
ejecta has a spatial resolution of 500 m/pixel and it is derived from images obtained by MES-
SENGER’s Mercury Dual Imaging System (MDIS) narrow-angle camera [8], while Raditladi
∗ Correspondingauthor
Email address: marchi@oca.eu (S. Marchi)
Preprint submitted to Planetary and Space Science May 27, 2011
2. basin and surrounding areas were imaged at 280 m/pixel. Both basins and surrounding areas
were also imaged with a set of 11 filters of the MDIS wide-angle camera (WAC), whose wave-
lengths range from 430 to 1020 nm [8]. These images were used to obtain color maps with a
resolution of about 5 km/pixel and 2.4 km/pixel for Rachmaninoff and Raditladi, respectively.
The two basins appeared to be remarkably young because of the small number of impact craters
seen within their rims [31, 24, 25]. For this reason it has been argued that they were likely formed
well after the end of the late heavy bombardment of the inner Solar System at about 3.8 Ga [31].
In particular, for Raditladi it has been pointed out that the basin could be as young as 1 Ga or
less [31, 25].
Interestingly, both basin floors are partially covered by smooth plains. In the case of Rach-
maninoff, an inner floor filled with spectrally distinct smooth plains has been observed and this,
combined with the small number of overimposed craters, implies a volcanic origin [25]. The
estimate of the temporal extent of the volcanic activity and, in particular, the timing of the most
recent activity may represent a key element in our understanding of the global thermal evolution
of Mercury, and helps to constrain the duration of the geologic activity on the planet in light of
the new data provided by MESSENGER. Moreover, Raditladi may be the youngest impact basin
discovered on Mercury so far, and therefore it is important to understanding the recent impact
history of the planet.
For all these reasons, the age determination of Rachmaninoff and Raditladi basins and their geo-
logically different terrains is of a great interest. In this paper, we will present a revised Mercury
crater chronology, and show how to take into account for the crustal properties of the target (§ 3).
This chronology will be then applied to Rachmaninoff and Raditladi basins (§ 4).
2. The Model Production Function chronology
In this paper we date the Raditladi and Rachmaninoff basin units by means of the the Model
Production Function (MPF) chronology of Mercury [16, 17]. This chronology relies on the
knowledge of the impactor flux on Mercury and on the computed ratio of impactors between
Mercury and the Moon. The absolute age calibration is provided by the Apollo sample radio-
metric ages. The crater scaling law enables computation of the crater size-frequency distribution
(SFD) using a combination of the impactor SFD and the inferred physical properties of the target.
The computed crater SFD per unit surface and unit time is the so-called MPF. The present model
involves several improvements with respect to the model presented in [16] and [17], thus it will
be described in detail in the next sections.
2.1. The impactor SFD and the crater scaling law
In the following analysis, we use the present Near-Earth Object (NEO) population as the
prime source of impactors. This assumption is justified by the presumably young ages (i.e. low
crater density) of the terrains studied in this paper. In particular, we use the NEO SFD as modeled
by [2, 3]. This NEO SFD is in good agreement with the observed NEO population, fireballs and
bolide events [see 16, for further details].
Concerning the crater scaling law, we adopted the so-called Pi-scaling law in the formulation
by [12]. Unlike previous approaches, our methodology explicitly takes into account the crustal
properties of the target. In fact, surfaces react differently to impact processes, depending on
the bulk density, strength and bulk structure of the target material. These latter parameters are
2
3. taken into account by the scaling law, and are tabulated for several materials like cohesive soils,
hard-rock and porous materials [e.g. 20, 12]. On a planetary body, terrain properties may vary
from place to place according to the local geological history and as a function of the depth in the
target crust. Therefore, impacts of different sizes taking place on a particular terrain may require
different estimates of the target properties.
The Pi-scaling law allows computation of the transient crater diameter (Dt ) as a function of
impact conditions and target properties, and reads:
2ν 2+µ ν(2+µ) µ
− 2+µ
gd ρ µ
Y 2
ρ µ
Dt = kd 2 + (1)
2v⊥ δ ρv2
⊥ δ
where g is the target gravitational acceleration, v⊥ is the perpendicular component of the
impactor velocity, δ is the projectile density, ρ and Y are the density and tensile strength of the
target, k and µ depend on the cohesion of the target material and ν on its porosity1. Therefore,
the nature of the terrain affects the crater efficiency and the functional dependence of the crater
size with respect to the input parameters (e.g. impactor size and velocity). Equation 1 accounts
both for the strength and gravity regimes, allowing a smooth transition between the two regimes.
The impactor size (d sg ) for which we have the transition between the two regimes is determined
by equating the two additive terms in equ. 1, therefore:
2+µ
ν
v2 Y 2
ρ
d sg = 2 ⊥ (2)
g ρv2
⊥ δ
The transient crater diameter is converted into final crater diameter (D) according to the
following expressions:
D = 1.3Dt if Dt ≤ D⋆ /1.3 (3)
D1.18
t
D = 1.4 0.18 if Dt > D⋆ /1.3 (4)
D⋆
where D⋆ is the observed simple-to-complex transition crater diameter, which for Mercury
is 11 km [23]. The conversion between transient crater to final crater is rather uncertain and
several estimates are available [e.g. 11, 19, 7]. Here we have used the factor 1.3 from transient
to final simple craters2 . For the complex craters, we use the expression proposed by [7], where
the constant factor has been set to 1.40 in order to have continuity with the simple crater regime
(1.4 = 1.31.18 ). We note that the effects of the material parameters on the transient crater size
depend on whether a crater is formed in the strength or gravity regime. For the strength regime,
D ∝ ρ−0.1 or ∝ ρ−0.2 , while D ∝ Y −0.2 or ∝ Y −0.3 according to the values for µ and ν given above.
In the gravity regime, D ∝ ρ−0.3 . In all cases, the dependence of D on both ρ and Y is mitigated
by the low exponents.
1 The values used are: k = 1.03 and µ = 0.41 for cohesive soils, while k = 0.93 and µ = 0.55 for rocks. ν has been set
to 0.4 in all cases [12].
2 The factor has been retrieved at http://keith.aa.washington.edu/craterdata/scaling/theory.pdf on January 2011.
3
4. 2.2. Inhomogeneities of the target material parameters
The application of the crater scaling law is not straightforward, since the physical parameters
of the terrains are poorly constrained for Mercury and the crater scaling law has been derived for
idealized uniform target properties. So far, no detailed and systematic study has been performed
to develop a crater scaling law for a layered target [e.g. 20, 5], although numerical modeling
of terrestrial craters has shown that the target layering plays an important role in the cratering
process [e.g. 6, and references therein]. On the other hand, we think that it is worth attempting
to simulate a more realistic situation instead of using the same average values for craters whose
sizes can vary by order of magnitudes and consequently involved different layers of a planetary
crust. In this context, geological analysis of the terrains can provide valuable information, at
least to constrain the surface properties of the target.
In this work, we assumed that the density and strength of Mercury varies as a function of the
depth, in analogy to that inferred for the Moon [16, and references therein]. In figure 1 (left
panels) the assumed density and strength profiles are indicated. These profiles are consistent
with the upper lunar structure [13], and were adopted also for Mercury. In particular, we have
considered a more or less fractured upper crust on top of a bulk silicic lower crust which in turn
overlays a peridotitic mantle. However, it must be emphasized that the depths at which these
layers occur may vary from place to place (see § 3).
For each impactor size, we have assigned average values for the target density and strength. Over
a wide range of parameters, the transient crater radius (Rt ) is about 10 − 20 times larger that the
impactor radius r and the depth of the crater is typically between one-fourth and one-third of the
crater size [20]. Thus the thickness of the excavated material is roughly between 2.5 − 7 impactor
radii. Here we have adopted an intermediate value, namely averaging the density and strength up
to a depth of 5r (see fig. 1, right panels) Given the limited variation in the density and strength
profile, the choice of the actual depth to average the density and strength for a given impactor
radius has a low influence (< 5%) on the scaling law.
In addition to the density and strength profiles, we also consider a transition of the crater scaling
law (from cohesive-soil to hard-rock) according to the size of the impactor. In fact, the density
and strength profiles shown in fig. 1 describe a material of increasing coherence for increasing
depth. This is the result of the continuous bombardment of planetary surfaces that produces
comminution and fracturing of the upper crustal layers gradually deacreasing with depth as ob-
served in seismic profiles of the lunar crust underneath the Mare Cognitum [32, 28, 14]. In this
respect, craters that affect only the upper fractured layers form in the cohesive-soil regime, while
larger ones in hard-rock regime. Therefore the depth of the transition (H) from the superficial
fractured layer to the unfractured lower crust is an important parameter. The depth (and therefore
the crater size) at which the transition from one regime to the other occurs can vary from place
to place. For instance, the thickness of the cohesive layer may be only of a few meters on recent
lunar mare material [26], while it is expected to be of several kilometers on the highlands3. In
the examples of fig. 1, it is assumed that H = 10 km [13].
The details of the transition are not easy to model. A simplified study of impact processes on a
layered target was performed by [26]. They simulated a two-layer structure, formed by a loose,
granular layer on top a more competent material. It was observed that the craters had the usual
shapes for diameters less than about 4 times of the top layer thickness. Larger craters devel-
oped central mounds, flat floors and concentric rims indicating the presence of the underlying
3 Note that, in principle, the above scenario maybe locally reversed, e.g. in the presence of fresh solidified lava on top
of an older fractured layer.
4
5. layer. According to these results, we simplify the problem by considering a sharp transition in
the crater scaling law, at Dt = 4H. This implies a transition as a function of impactor radius
at r = H/5 − H/10. The effect of the transition in the scaling law is reported in fig. 2 for two
depths of transitions. Note that the position of the sharp transition varies according to the depth
assumed. In this paper, we use an intermediate value and set the transition at r = H/7.5. In a
more realistic situation, a gradual transition should be predicted given that the target gradually
changes its properties as function of the depth. Therefore, our simplified model is not expected
to be accurate close to the transition region, nevertheless we believe it provides a reasonable way
to approach the cratering scaling law for a layered target.
2.3. Deriving the Model Production Function
The NEO population and the crater scaling described in the previous section are used to derive
the MPF per unit time (see fig. 3). The main outcome of our model is that the adopted transition
in the crater scaling law results into a “S-shaped” feature (or flexure) in the MPF. The position
of such feature, which is determined by H, is not known a-priori. However, as discussed in [17],
in some cases H can be constrained by the shape of the observed crater SFD. Furthermore, the
geological analysis of the terrains can help to derive the expected range of variation for H. For
instance, lava emplacements may partly strengthen or even completely replace the pre-existing
fractured layer. Hence in this latter cases the fractured horizon can be confined within a very thin
regolith cover, negligible for our calculation (H ∼ 0). For young units with poor crater statistics,
the choice of H may affect the age determinations by up to a factor of 3-4. Thus, in order to
derive a more accurate age estimate, it is of paramount importance to adapt the crater production
function to the nature of the terrains investigated.
The absolute age is given by the lunar chronology, which expresses the lunar crater cumulative
number at 1 km (N1 ) as a function of time (t), using the following equation:
N1 (t) = a(ebt − 1) + ct (5)
−15 −3
where a = 1.23 × 10 , b = 7.85, c = 1.30 × 10 [16]. The MPF function at a time t is
given by:
N1 (t)
MPF(t) = MPF(1yr) · (6)
N1 (1yr)
The MPF(t) is used to derive the model cratering age by a best fit procedure that minimizes
the reduced chi squared value, χ2 . Data points are weighted according to their measurement
r
errors. The formal errors on the best age correspond to a 50% increase of the χ2 around the
r
minimum value.
It must be realized that the formal statistical error on the model age only reflects the quality
of the crater SFDs. On top of that, other sources of uncertainties are present. They stem from
the uncertainties involved in the physical parameters used in the model, although we want to
stress here that the model ages are not very sensitive to details of the density and strength profile
[see § 3.1 of 16]. A more important issue is the applicability of the present NEO population
in the past. The N1 (t) chronology function assumes a linear dependence with time in the last ∼
3.8 Ga, corresponding to an impactor population in a steady state. On the other hand, dynamical
studies of recent main belt asteroid family formation suggested that the present NEO flux may be
higher that the average steady flux by a factor of 2 [4]. This result also agrees to what found by
5
6. cratering studies of young lunar terrains [< 0.8 Ga; e.g. 16]. Concerning the layering structure,
as described above, the choice of H might affect the age estimate by a factor of 3-4 at most. The
uncertainty due to the layering is, nevertheless, typically present only for young terrains where
the crater SFD has a limited range of crater dimensions. The layering affects the specific shape
of the crater SFD, and has to be evaluated case by case, as it will be discussed in detail in the
following sections. Finally, it must be noted that wavy features in the crater SFD can be due also
to other processes than layering, like for instance partial crater obliteration due to subsequent lava
flows. Therefore, the nature of the S-shaped feature must be constrained as much as possible by
geological analysis in order to achieve a more reliable age determination.
3. Geological analysis and model ages
Geological maps of the Rachmaninoff and Raditladi basins were constructed considering
both floors and ejecta. For the floor terrains, the geological units were identified on the base of
their different surface morphologies and spectral characteristics (i.e., albedo), along with an anal-
ysis of their stratigraphic relationships. The ejecta units, surrounding the basins, were outlined
considering exclusively the area of continuous ejecta blankets, which are easily detectable thanks
to their characteristic hummocky surface. The geological maps also take into account tectonic
features affecting the areas.
Crater age determination is based on the primary craters, i.e. those formed by impacts with ob-
jects in heliocentric orbits. Hence, a crucial point in assessing age by crater counts is to identify
and avoid secondary craters. Most of the secondaries are recognizable because they are directly
related to their primaries (e.g., the secondaries are arranged in radial patterns around the pri-
mary), or occurr in loops, cluster and chains. The contribution of far-field secondaries, which are
normally not distinguishable from primary craters [e.g. 18], has been neglected. Although this is
a reasonable assumption for Rachmaninoff and Raditladi basins given their low crater densities
and thus their presumable relatively young ages, MPF model ages may overestimate real ages.
3.1. Rachmaninoff basin
The Rachmaninoff basin is surrounded by a continuous ejecta blanket and includes an inte-
rior peak ring structure, about 136 km in diameter, with extended smooth plains filling its floor.
Most of the basin walls are modified into terraces. Several different geological units have been
distinguished inside the floor on the basis of their different relative albedo and surface texture
(fig. 4). The inner smooth plains are mostly within the peak ring except in the southern quadrant
of Rachmaninoff, where the smooth plains cover or embay the peak ring structure and some of
the annular units within the rim. This observation suggests an origin of volcanic emplacement.
In the WAC enhanced-color images these plains show a yellow to reddish tone which stands out
from the darker and bluer color of the other units within the basin and surrounding regions [25].
This clearly supports a different composition and origin of these inner smooth plains. Several
discontinuous and concentric troughs possibly due to the uplift and extension of the basin floor,
affect the area enclosed by the peak ring [25] and have been interpreted to be graben. The an-
nular region between the peak ring and the rim basin includes seven different units. The most
prominent is made up of bright materials, apparently younger than all the other units and possibly
related to explosive volcanism [25]. Peak ring and terrace material boundaries stand out for their
relief, whereas hummocky, dark, irregular and annular smooth plains do not show unequivocal
6
7. Table 1: Statistics of all the features detected on Rachmaninoff and Raditladi basin floors and ejecta. “All” indicates
all crater-like features, “Bon” the bonafide craters, “Sec” secondary craters (which includes chain, cluster and elliptical
craters), “End” endogenic (volcanic and tectonic) features. “Inn. pl.” and “Ann. un.” stand for inner plain and annular
unit, respectively.
Rach Rad
Count Inn. pl. Ann. un. Ejecta Inn. pl. Ann. un. Ejecta
All 37 119 1154 231 214 1518
Bon 13 51 180 79 96 452
Sec 1 46 974 34 91 1029
End 23 22 0 118 27 37
stratigraphic relationships with each other [25]. This suggests an almost coeval origin of these
units that may consist of impact melts and breccias. This is furthermore confirmed by the WAC
images, where annular units do not reveal any color variations and are characterized by uniform
blue color similar to the surrounding terrain. To shed more light on the origin of the floor ma-
terial we dated the Rachmaninoff basin using crater statistics of annular units and inner plains
separately. Bright material was neglected in the crater counts due to its limited extent. Craters in
the ejecta blanket were counted as well (fig. 4).
Easily recognizable secondary craters (either elliptical in shape or arranged in loops and chains)
have not been detected within the Rachmaninoff inner plains but numerous pits up to 3.5 km in
diameter have been found in close proximity to the concentric grabens. These features are very
unlikely to be impact craters and in our interpretation are most probably of tectonic (structural
pits, fault bounded depressions, en-echelon structures) and/or volcanic (more or less irregular
vents) origin (fig. 5, panels A and B). For this reason their counts were neglected for the purposes
of age determination. Clusters and chains of secondaries with irregular and elliptical shapes were
recognized in the western sector of the annular units and appear to be directly related to a nearby
60 km primary peak crater overlying the Rachmaninoff ejecta (fig. 5, panels C and D). Self sec-
ondaries are numerous within the ejecta blanket.
The resulting crater count statistics are reported in Table 1 where for each terrain, all crater-like
features, bonafide craters, secondary craters and endogenic (namely volcanic or tectonic) fea-
tures are listed. It is interesting to compare the SFDs of all the counts (fig. 6). According to our
best interpretation of the detected features, the inner plains contain more endogenic features than
bonafide craters. Hence, in our opinion the uneven distribution in R plots of crater-like features
smaller than 4 km, which is generally attributed to the effect of far field secondaries on Mercury
[31], are in this case dominated by tectonic and volcanic features. For the annular units, both
the secondary crater and endogenic SFDs have steeper slopes with respect to the bonafide crater
SFD, moreover they are limited to features smaller than 4-5 km. Hence, for the annular units as
well as the inner plains, the identification of endogenic features is clearly very important since
it heavily affects the final bonafide crater SFD. On the ejecta, most of the crater-like features
appear to be self secondaries mostly arranged into clusters and chains and/or with an elliptical
shape. All the terrains were dated using their bonafide crater SFDs.
The MPF fits of the observed crater SFDs are shown in figure 7. The lower panel shows the
distribution of bonafide primary impact craters detected on the ejecta blanket. A remarkable fea-
ture in the crater SFD of the ejecta is the presence of a flexure point at about D = 15 km. The
actual shape of the bonafide crater SFD is partially due to the feature selection. Nevertheless, we
think that at the large crater sizes relevant here, our selection is reliable and, consequently, the
7
8. observed flexure point is likely a real feature possibly reflecting a layered target with an upper
weak horizon. Hence the MPF best fit is achieved with H = 3 km and gives a model age of
3.54 ± 0.1 Ga.
In fig. 7 (upper panel) the bonafide crater SFD on inner plains and annular units are shown. Note
that, unlike the ejecta, both cases do not show the presence of a flexure point. This may be due to
a real absence of an upper weak horizon or to the lack of large craters that would have otherwise
allowed to retrieve information on the geomechanical properties of the deep crustal layers. The
annular units are composed of breccias more or less welded by impact melts which can have only
partially strengthened the fractured material either pre-dating or originating from the Rachmani-
noff impact. Hence, it is reasonable to assume at least the same H of the crust beneath the ejecta.
This leads to a model age of 3.6 ± 0.1 Ga, which is consistent with the model age of the ejecta
and likely dates the Rachmaninoff impact event.
The inner plains are characterized by much poorer statistics within a small range of diameters,
therefore the crater SFD cannot be used to infer H. Nevertheless, geological analysis suggest that
the inner plains are younger volcanic flows on the basis of their different albedo, color and over-
lapping relationship with respect to the unit emplaced between the peak-ring and the basin rim
[25]. This would make possible also the scenario in which the former fractured horizon, either
pre-dating or originating from the impact itself, was completely hardened by the rising magmas
and emplacement of lava fields (fig. 8a). In this case, the MPF acceptably fits the bonafide crater
size distribution giving a model age of 0.7 ± 0.2 Ga (fig. 7). By contrast the fit would be very
poor if the all crater-like features would be taken into account. This is not surprising considering
the strong contribution we infer that tectonic and volcanic features have on the inner plains statis-
tics. Another possible scenario is that the magmatic activity within Rachmaninoff was unable to
totally strengthen the upper weak layer comprising of fractured material originated by the impact
itself or inherited by primordial events. This could be due to either weakly sustained volcanism,
which emplaced a thin volcanic sequence on top of a fractured material, and/or, a magma influx
concentrated along few well defined conduits within a still fractured crust underneath the basin
(fig. 8b). In this case we also computed the model age using H = 3 km as for the annular units
and ejecta, obtaining a value of 1.5 ± 0.4 Ga. In both cases (upper weak crustal layer absent
or preserved) the inner plains turn out to be remarkably young, and demonstrate that a recent
volcanic activity occurred within the basin.
3.2. Raditladi basin
Raditladi contains an interior peak-ring structure 125 km in diameter and its walls appear to
be degraded, with terraces most pronounced within the north and west sides of the rim [24]. A
continuous ejecta blanket with no visible system of rays surrounds the basin and extends up to
225 km from the basin rim (Fig. 9). The floor is partially filled with smooth, bright reddish plains
material that clearly embays the rim and the central peak ring [1, 24]. The northern and southern
sectors of the basin floor consist of dark, relatively blue hummocky plains material confined be-
tween the rim and the peak ring. Troughs are found close to the center of the basin arranged in
a partially concentric pattern, ∼70 km in diameter, and are interpreted either as graben resulting
from post-impact uplift of the basin floor, or as circular dikes possibly representing fissural feed-
ing vents [9, 25]. Floor material was subdivided into two different units following [24]: smooth
and hummocky plains. Smooth plains may have a volcanic origin, as appears to be the case
for plains in the nearby Caloris basin [9, 27], however no clear stratigraphic relation with the
hummocky plains has been found, suggesting that all the different terrains within Raditladi basin
8
9. may be coeval and directly related to the impact [25]. With respect to the ejecta area, we have
selected the hummocky continuous ejecta blanket surrounding the basin.
We performed a crater count of the inner plains within the peak ring and the annular units en-
closed between the basin rim and the peak ring. Counts were also performed on the ejecta
blankets.
Within the inner plains, numerous small graben-related pits up to 5 km in diameter are identified;
as for the case of Rachmaninoff, they are most probably tectonically-originated features and/or
volcanic vents (fig. 10, panels A and B). Specifically, two peculiar pits in the northern inner
plains were interpreted as volcanic vents for the dark material on the crater floor [9]. Secondary
craters have been found associated to a 23-km crater within the inner plains (fig. 10, panels A
and C). Some secondaries are also present on the annular plains, whereas the ejecta blanket is
characterized by numerous self secondary craters, occurring mainly in clusters and chains. Fig-
ure 9 shows the bonafide craters. The statistics of all the identified features are reported in table
1, whereas the corresponding SFDs are shown in fig. 11.
The cumulative bonafide crater SFDs for different terrains of the Raditladi basin are shown in
fig. 12, along with the MPF model ages.
The measured crater SFD on the ejecta blanket shows a flexure at about D = 2 − 3 km. The
position of the flexure is well above the size of craters that can no longer be distinguished be-
cause of the image resolution, nevertheless the contribution of secondary craters at these crater
sizes might be important. In the assumption that this feature is due to the layering, the best fit
achieved for H = 0.4 km gives a model age of 1.3 ± 0.1 Ga. The best fit for the annular units is
achieved using H = 0.7 km and the resulting model age is 1.1 ± 0.1 Ga. These values are con-
sistent with both the layering and model age inferred for the ejecta blankets. For this reason the
basin formation can be reliably fixed at around 1.1-1.3 Ga in accordance with the age suggested
by [31] on the basis of a relative-chronology approach. As for the Rachmaninoff basin, the poor
statistics and the limited range of diameters imply that the inner plains SFD cannot be used to
constrain H. We derived the model age with both the same H of the annular units (H = 0.7 km),
and a negligible thickness (H ∼ 0), obtaining 2.2 ± 0.3 Ga and 1.1 ± 0.1 Ga, respectively. The
former model age leads to a paradox given that the annular units are certainly coeval with the
basin formation and, consequently, must only be older or of the same age as the smooth plains.
Hence, the most reliable result for the inner plains is to consider a solid material yielding a crater
retention age of about 1.1 Ga. The solid material could be due to an emplacement of lavas soon
afterward the impact leading to a complete hardening of the fractured and brecciated material
within the basin (fig. 13a). This interpretation is consistent with the presence of volcano-tectonic
features within the basin but may conflict with both the absence of distinctive color variations of
the inner plains with respect to the surrounding areas and their unclear stratigraphic relationship
with the annular units. Alternatively, a great amount of impact melts able to completely harden
the impact breccias may explain the derived crater retention age (fig. 13b).
4. Discussion and conclusions
MPF crater chronology has been applied to date the Rachmaninoff and Raditaldi basins.
Age assesment has been performed taking into account target rheological layering and using the
present NEO population as the prime source of impactors.
Our results demonstrate that the volcanic activity within the Rachmaninoff basin interior signifi-
cantly post-dates the formation of the basin. The basin itself probably formed about 3.6 Ga ago,
whereas the volcanic inner plains may have formed less than 1 Ga ago. Therefore, Mercury had
9
10. a prolonged volcanic activity, which possibly persisted even longer than on the Moon, where the
youngest detected nearside flows [on Oceanus Procellarum; 10] are about 1.1 Ga old. On the
other hand, the Raditladi basin has an estimated model age of about 1 Ga and no firm indication
that the inner plains formed more recently than the basin itself. Hence, these plains may be due
to either huge volumes of impact melts or lavas emplaced soon afterward the basin formation. In
the latter case, which is not clearly supported by the stratigraphic observations, volcanism might
have been triggered by the impact itself.
This work also shows the role of target properties in deriving the age of a surface. Where such
properties are neglected, as in traditional chronologies [e.g. 22], the crater production function
may be unable to accurately reproduce the observed crater SFD and/or to provide a consistent
age for nearby terrains. The following examples serve to illustrate this point: the Rachmaninoff
ejecta bonafide crater SFD shows an S-shaped feature that, according to our best knowledge,
cannot be ascribed to processes other than a layered target; the Raditladi inner plains have an
higher density of craters than the annular units, implying a paradoxically older age for the inte-
rior plains if the inner and outer plains had the same material properties.
The derived ranges of ages for Raditladi basin imply that its formation occurred long after the
late heavy bombardment (∼ 3.8 Ga), at a time when the primary source of impactors was a NEO-
like population. This conclusion also likely applies to Rachmaninoff basin, even if it cannot be
excluded that it was formed during or prior the late heavy bombardment. The NEOs average
impact velocity on Mercury is about 42 km/s [15]. Considering a most probable impact angle
of π/4, the projectiles responsible for Rachmaninoff and Raditladi formation should have had
diameters in the range 14-16 km (see fig. 2). In the present NEO population, bodies are quickly
replenished -in time scales of tens of Myrs- mainly from the main belt via slow orbital migration
into major resonances. Such a migration, due mainly to Yarkowsky effect, is size dependent and
is negligible for objects larger than ∼ 10 km. Therefore larger objects, such as those required
for the formation of the Raditladi and Rachmaninoff basins, are mainly produced by dynamical
chaos loss [21]. Those simulations show that the rate of large impactors decreased by a factor
of 3 over the last 3 Ga. Another source of large impactors is the sporadic direct injection into
strong resonances due to collisions [34]. The present NEOs’ average impact probability with
Mercury in the size range of 14-16 km, is of about one impact every 3.3 Ga, in agreement with
the proposed timescales of the formation of Rachmaninoff and Raditladi.
10
11. Acknowledges
The authors wish to thank P. Michel for helpful discussions on the cratering processes on a
layered target. We also wish to thank A. Morbidelli for discussions regarding the NEO popu-
lation. Finally, we thank the referees (C. Chapman and an anonymous one) for providing very
interesting comments, that helped to improve our work.
References
[1] Blewett D.T., Robinson M.S., Denevi B.W., Gillis-Davis J.J., Head J.W., Solomon S.C., Holsclaw G.M., McClin-
tock W.E., 2009. Multispectral images of Mercury from the first MESSENGER flyby: Analysis of global and
regional color trends. Earth Planet. Sci. Lett., 285(3-4), 272-282.
[2] Bottke, W. F., Jedicke, R., Morbidelli, A., Petit, J.-M., & Gladman, B. 2000. Understanding the Distribution of
Near-Earth Asteroids. Science, 288, 2190-2194.
[3] Bottke, W. F., Morbidelli, A., Jedicke, R., Petit, J.-M., Levison, H. F., Michel, P., & Metcalfe, T. S. 2002. Debiased
Orbital and Absolute Magnitude Distribution of the Near-Earth Objects. Icarus, 156, 399-433.
[4] Bottke, W. F., Vokrouhlick´ , D., & Nesvorn´ , D. 2007. An asteroid breakup 160 Myr ago as the probable source of
y y
the K/T impactor. Nature, 449, 48-53.
[5] Collins, G. S., Melosh, H. J., & Marcus, R. A. 2005. Earth Impact Effects Program: A Web-based computer
program for calculating the regional environmental consequences of a meteoroid impact on Earth. Meteorit. Planet.
Sci., 40, 817-840.
[6] Collins, G. S., Kenkmann, T., Osinski, G. R., W¨ nnemann, K. 2008. Mid-sized complex crater formation in mixed
u
crystalline-sedimentary targets: Insight from modeling and observation. Meteorit. Planet. Sci., 43, 1955-1977.
[7] Croft, S. K. 1985. The scaling of complex craters. Proc. Lunar Planet. Sci. Conf., 15, 828-842.
[8] Hawkins, S.E., Boldt, J.D., Darlington, E.H., Espiritu, R., Gold, R.E., Gotwols, B., Grey, M.P., Hash, C.D., Hayes,
J.R., Jaskulek, S.E., Kardian, C.J., Keller, M.R., Malaret, E.R., Murchie, S.L., Murphy, P.K., Peacock, K., Prockter,
L.M., Reiter, R.A., Robinson, M.S., Schaefer, E.D., Shelton, R.G., Sterner, R.E., Taylor, H.W., Watters, T.R.,
Williams, B.D., 2007. The Mercury Dual Imaging System on the MESSENGER Spacecraft. Space Sci. Rev., 131,
247-338.
[9] Head J.W., Murchie S.L., Prockter L.M., Solomon S.C., Strom R.G., Chapman C.R., Watters T.R., Blewett D.T.,
Gillis-Davis J.J., Fassett C.I., Dickson J.L., Hurwitz D.M., Ostrach L.R., 2009. Evidence for intrusive activity on
Mercury from the first MESSENGER flyby. Earth Planet. Sci. Lett., 285(3-4), 251-262.
[10] Hiesinger, H., Head, J. W., III, Wolf, U., & Neukum, G. 2001. New Age Determinations of Lunar Mare Basalts
in Mare Cognitum, Mare Nubium, Oceanus Procellarum, and Other Nearside Mare. Lunar Planet. Inst. Sci. Conf.
Abstracts, 32, 1815.
[11] Holsapple, K. A. 1993. The scaling of impact processes in planetary sciences. Annu. Rev. Earth Planet. Sci., 21,
333-373.
[12] Holsapple, K. A., Housen, K. R. 2007. A crater and its ejecta: An interpretation of Deep Impact. Icarus, 187,
345-356.
[13] H¨ rz, F., Grieve, R., Heiken, G., Spudis, P., and Binder, A. 1991. Lunar surface processes. In Lunar Sourcebook:
o
A User’s Guide to the Moon (G. H. Heiken, D. T. Vaniman, and B. M. French, eds.) Cambridge University Press,
Cambridge. 61-120.
[14] Khan, A.K. Mosegaard, K.L. Rasmussen. 2000. A new seismic velocity model for the Moon from a Monte Carlo
inversion of the Apollo lunar seismic data. J. Geophys. Res. Lett., 27(11), 1591-1594.
[15] Marchi, S., Morbidelli, A., Cremonese, G. 2005. Flux of meteoroid impacts on Mercury. Astron. Astrophys., 431,
1123-1127.
[16] Marchi, S., Mottola, S., Cremonese, G., Massironi, M., Martellato, E. 2009. A New Chronology for the Moon and
Mercury. Astron. J., 137, 4936-4948.
[17] Massironi, M., Cremonese, G., Marchi, S., Martellato, E., Mottola, S., Wagner, R.J. 2009. Mercury chronology
revisited through MPF application on Mariner 10 data: new geological implications. J. Geophys. Res. Lett., 36,
21204.
[18] McEwen, A. S., & Bierhaus, E. B. 2006. The Importance of Secondary Cratering to Age Constraints on Planetary
Surfaces. Annu. Rev. Earth Planet. Sci., 34, 535-567.
[19] McKinnon, W. B., & Schenk, P. M. 1985. Ejecta Blanket Scaling on the Moon and - Inferences for Projectile
Populations. Lunar Planet. Inst. Sci. Conf. Abstract, 16, 544.
[20] Melosh, H. J., 1989. Impact Cratering: A Geologic Process. Oxford University Press, New York 1989, pp. 245.
[21] Minton, D. A., & Malhotra, R. 2010. Dynamical erosion of the asteroid belt and implications for large impacts in
the inner Solar System. Icarus, 207, 744-757.
11
12. [22] Neukum, G., & Ivanov, B. A. 1994, Hazards Due to Comets and Asteroids, 359.
[23] Pike, R. J. 1988. Geomorphology of impact craters on Mercury. Mercury (A89-43751 19-91). Tucson, AZ, Univer-
sity of Arizona Press, 1988, p. 165-273.
[24] Prockter, L.M., Watters, T.R., Chapman, C.R., Denevi, B.W., Head, J.W., Solomon, S.C., Murchie, S.L., Barnouin-
Jha, O.S., Robinson, M.S., Blewett, D.T., Gillis-Davis, J. 2009. The Curious Case of Raditladi Basin. Lunar Planet.
Sci. Conf. Abstract, 40, 1758.
[25] Prockter, L.M., Ernst, C.M., Denevi, B.W., Chapman, C.R., Head III, J.W., Fassett, C.I., Merline, W.J., Solomon,
S.C., Watters, T.R., Blewett, D.T., Cremonese, G., Marchi, S., Massironi, M., Barnouin, O.S. 2010. Evidence for
young volcanism on Mercury from the third MESSENGER flyby. Science, 329, 668-671.
[26] Quaide, W. L., & Oberbeck, V. R. 1968. Thickness Determinations of the Lunar Surface Layer from Lunar Impact
Craters. J. Geophys. Res., 73, 5247.
[27] Robinson M.S., Murchie S.L., Blewett D.T., Domingue D.L., Hawkins S.E., Head J.W., Holsclaw G.M., McClin-
tock W.E., McCoy T.J., McNutt R.L., Prockter L.M., Solomon S.C., Watters T.R. 2008. Reflectance and Color
Variations on Mercury: Regolith Processes and Compositional Heterogeneity. Science, 321, 66-69.
[28] Simmons G., Todd T., Wang H. 1973. The 25 km discontinuity: Implications for lunar history. Science, 182,
158-161.
[29] Steffl, A. J., Cunningham, N. J., Durda, D. D., & Stern, S. A. 2009, AAS/Division for Planetary Sciences Meeting
Abstracts, 41, #43.01
[30] St¨ ffler, D., & Ryder, G. 2001. Stratigraphy and Isotope Ages of Lunar Geologic Units: Chronological Standard
o
for the Inner Solar System. Space Sci. Rev., 96, 9-54.
[31] Strom, R.G., Chapman, C.R., Merline, W.J., Solomon, S.C., Head, J.W. 2008. Mercury Cratering Record Viewed
from MESSENGER’s First Flyby. Science, 321, 79.
[32] Tokosoz M.N., Press F., Dainty A., A., Anderson K., Latham G., Ewing M. Dorman J., Lammlein D., Sutton
G., Duennebeir F. 1972. Structure composition and properties of lunar crust. Proc. Lunar Planet. Sci. Conf., 3,
2527-2544.
[33] Wagner, R., Head, J. W., Wolf, U., & Neukum, G. 2002. Stratigraphic sequence and ages of volcanic units in the
Gruithuisen region of the Moon. J. Geophys. Res., 107, 5104
[34] Zappala, V., Cellino, A., di Martino, M., Migliorini, F., & Paolicchi, P. 1997. Maria’s Family: Physical Structure
and Possible Implications for the Origin of Giant NEAs. Icarus, 129, 1-20.
12
13. 50 20
40
15
Impactor diameter (km)
30
Depth (km)
10
20
5
H
10
0 0
2 2.5 3 3.5 2 2.5 3 3.5
3 3
Target density (g/cm ) Target density (g/cm )
50 20
40
15
Impactor diameter (km)
30
Depth (km)
10
20
5
H
10
0 0
0 1×10
8
2×10
8
3×10
8 0 1×10
8
2×10
8
3×10
8
2 2
Target strength (dyne/cm ) Target strength (dyne/cm )
Figure 1: Inferred density and strength profiles for Mercury. Left panels report the assumed profiles as a function of
depth. The discontinuous transitions correspond to the major transitions in the crust, in analogy to the lunar crust. The
depth of the upper cohesive layer (H) is also indicated for clarity. In this example, it has been set to 10 km. The right
panel shows the averaged density and stregth as a function of the impactor diameter. This result has been achieved by
averaging, for an impactor of radius r, both the density and strength up to a depth of 5r (see text).
13
14. 10d
20d
H&H Df sand (average=5r)
H&H Df hard (average=5r)
Df trans (5r, r<H/10)
2 Df trans (5r, r<H/5)
10
Crater diameter, D (km)
1
10
0
10 -1 0 1
10 10 10
Impactor diameter, d (km)
Figure 2: Crater scaling laws from Mercury. The plot reports the crater scaling laws for both cohesive material (dashed
red line) and hard-rock material (solid red line). Two examples of the scaling law corresponding to the layered target
are shown. They correspond to a transition in the crater scaling law for impactor radius r = H/10 (green dashed line)
and r = H/5 (blue dashed line). These values correspond to the predicted uncertenties in the modeling of the transition
(see text), and in the rest of the work we adopt an intermediate value of r = H/7.5. The depth of the cohesive layer H
has been set to 10 km and density and strength are averaged to a depth of 5r. In all cases, the curves are derived for the
average impact velocity of 42 km/s, and an impact angle of π/4. The estimated impactor sizes that formed Rachmaninoff
and Raditladi basins are also shown.
14
15. -11
10
H=0 km
H=0.7 km
H=3 km
-12
10
Cumulative number of craters (km yr )
-1
-2
-13
10
-14
10
-15
10
-16
10 1 10 100
Crater diameter (km)
Figure 3: Examples of computed crater size-frequency diatributions per unit surface per unit time (the so-called Model
Production Function, MPF) obtained with three different values of H, which will be used for the age assesment of
Rachmaninoff and Raditladi basin. In all cases, the transition in the scaling law is set at r = H/7.5. Depending on the
relative position of the S-shaped feature with respect to the crater SFD, a maximum age variation of a factor 3-4 can
occur.
15
16. Figure 4: Upper panel: Rachmaninoff geological sketch. Lower panel: Bonafide craters within the three regions con-
sidered for crater counts. Boundaries and bonafide craters are in yellow for the inner plains, green for the annular units
and red for the ejecta blankets. The counting areas are: 1.74×104 , 4.67×104 and 3.32×105 km2 for inner plains, annular
units and ejecta blanket, respectively. Boxes indicate close views of fig. 5.
16
17. Figure 5: A) Close view of the plains within the Rachmaninoff peak ring: red circles = bonafide craters, yellow circles =
circular features of endogenic origin; green circles = secondary craters. B) Detail of endogenic features (white arrows),
often with irregular shapes and generally related to troughs and/or surrounded by brighter aloes. C) Close view of a
primary peak crater (60 km of diameter) and related secondary craters: red cicles = bonafide craters, yellow circles =
circular features of endogenic origin; green circles = secondary craters . D) Detail of secondary craters (white arrows)
often with elliptical shapes and associated in chains and loops.
17
18. Rach. Basin (inn. pl.) Rach. Basin (ann. un.)
All crater-like features All crater-like features
Bonafide craters Bonafide craters
Endogenic features Secondary craters
Endogenic features
-3
10
Cumulative number (km )
-2
-4
10
-5
10 1 1 10
Crater diameter (km) Crater diameter (km)
Rach. Basin ejecta
-2
10 All crater-like features
Bonafide craters
Secondary craters
Cumulative number of craters (km )
-2
-3
10
-4
10
-5
10
-6
10 1 10 100
Crater diameter (km)
Figure 6: Rachamaninoff basin SFDs of the detected features for inner plains and annular units (upper panels) and ejecta
(lower panel).
18
19. Rach. Basin (inn. pl.) Rach. Basin (ann. un.)
Bonafide craters Bonafide craters
+0.4 +0.1
1.5 -0.4 Ga (H=3 km) 3.6 -0.1 Ga (H=3 km)
+0.2
0.7 -0.2 Ga (H=0 km)
-3
10
Cumulative number (km )
-2
-4
10
-5
10 1 1 10
Crater diameter (km) Crater diameter (km)
Rach. Basin ejecta
-2
10 Bonafide craters
+0.1
3.5 -0.1 Ga (H=3 km)
Cumulative number of craters (km )
-2
-3
10
-4
10
-5
10
-6
10 1 10 100
Crater diameter (km)
Figure 7: Rachmaninoff age assessment. MPF best fit of the bonafide crater SFDs for the inner plains and annular units
(upper panels) and ejecta (lower panel).
19
20. Figure 8: Possible geological sections of the Rachmaninoff basin hypothesized from the fit of MPF with the crater SFD
of ejecta, annular materials and inner plains: a) rising magmas and lavas completely hardened the former horizon made
up of primordial and impact related fractured material (H = 0 km); b) a weakly sustained volcanism emplaced a thin lava
layer on top of the fractured material with magma influx concentrated along few conduits (H =0.7 km).
20
21. Figure 9: Upper panel: Raditladi geological sketch. Lower panel: Bonafide craters within the three regions (inner plains,
annular units, and ejecta blanckets) considered for crater counts. Boundaries and bonafide craters are in yellow for the
inner plains, green for the annular units and red for the ejecta blankets. The counting areas are: 1.95×104 , 3.39×104 and
2.01×105 km2 for inner plains, annular units and ejecta blanket, respectively. Boxes indicate close view of fig. 10.
21
22. Figure 10: A) Close view of the plains within the Raditladi peak ring: red circles = bonafide craters, yellow circles =
circular features of endogenic origin; green circles = secondary craters. B) Detail of endogenic features (white arrows),
often with irregular shapes and generally related to troughs and/or surrounded by brighter aloes. D) Close view of a
primary peak crater (18 km of diameter) and related secondary craters (white arrows).
22
23. Raditladi Basin (inn. pl.) Raditladi Basin (ann. un.)
-2
10 All crater-like features All crater-like features
Bonafide craters Bonafide craters
Secondary craters Secondary craters
Endogenic features Endogenic features
Cumulative number of craters (km )
-2
-3
10
-4
10
-5
10 1 10 1 10
Crater diameter (km) Crater diameter (km)
-2
10
Raditladi Basin ejecta
All crater-like features
Bonafide craters
Secondary craters
Endogenic features
Cumulative number of craters (km )
-2
-3
10
-4
10
-5
10 1 10
Crater diameter (km)
Figure 11: Raditladi basin SFDs of the detected features for inner plains and annular units (upper panels) and ejecta
(lower panel).
23
24. Raditladi Basin (inn. pl.) Raditladi Basin (ann. un.)
-2
10 Bonafide craters Bonafide craters
+0.3 +0.1
2.2 -0.3 Ga (H=0.7 km) 1.1 -0.1 Ga (H=0.7 km)
+0.1
1.1 -0.1 Ga (H=0 km)
Cumulative number of craters (km )
-2
-3
10
-4
10
-5
10 1 10 1 10
Crater diameter (km) Crater diameter (km)
-2
10
Raditladi Basin ejecta
Bonafide craters
+0.1
1.3 -0.1 Ga (H=0.4 km)
Cumulative number of craters (km )
-2
-3
10
-4
10
-5
10 1 10
Crater diameter (km)
Figure 12: Raditladi age assessment. MPF best fit of the bonafide crater SFDs for the inner plains and annular units
(upper panels) and ejecta (lower panel).
24
25. Figure 13: Possible geological sections of Raditladi basin hypothesized from the fit of MPF with the crater SFD of
ejecta, annular materials and inner plains. Two scenarios can be argued to justify a very low value of H for the inner
plains a) lavas emplaced soon afterward the impact hardened the fractured and brecciated material within the basin or, b)
impact melts completely hardened or replaced the impact breccias.
25