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Sean C Solomon - One of the best experts on this subject based on the ideXlab platform.

  • Measurement of the radius of Mercury by radio occultation during the MESSENGER flybys
    2020
    Co-Authors: Mark E Perry, Maria T Zuber, David E Smith, Sean C Solomon, Olivier S. Barnouin, Roger J Phillips, Daniel S Kahan, Carolyn M Ernst, Dipak K Srinivasan, Jürgen Oberst
    Abstract:

    a b s t r a c t The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) Spacecraft completed three flybys of Mercury in [2008][2009]. During the first and third of those flybys, MESSENGER passed behind the planet from the perspective of Earth, occulting the radio-frequency (RF) transmissions. The occultation start and end times, recovered with 0.1 s accuracy or better by fitting edgediffraction patterns to the RF power history, are used to estimate Mercury's radius at the tangent point of the RF path. To relate the measured radius to the planet shape, we evaluate local topography using images to identify the high-elevation feature that defines the RF path or using altimeter data to quantify surface roughness. Radius measurements are accurate to 150 m, and uncertainty in the average radius of the surrounding terrain, after adjustments are made from the local high at the tangent point of the RF path, is 350 m. The results are consistent with Mercury's equatorial shape as inferred from observations by the Mercury Laser Altimeter and ground-based radar. The three independent estimates of radius from occultation events collectively yield a mean radius for Mercury of 2439.2 7 0.5 km

  • characterization of the morphometry of impact craters hosting polar deposits in mercury s north polar region
    Journal of Geophysical Research, 2012
    Co-Authors: Matthieu J. Talpe, Gregory A Neumann, Maria T Zuber, Sean C Solomon, E Mazarico, Di Yang, F Vilas
    Abstract:

    [1] Earth-based radar images of Mercury show radar-bright material inside impact craters near the planet's poles. A previous study indicated that the polar-deposit-hosting craters (PDCs) at Mercury's north pole are shallower than craters that lack such deposits. We use data acquired by the Mercury Laser Altimeter on the MESSENGER Spacecraft during 11 months of orbital observations to revisit the depths of craters at high northern latitudes on Mercury. We measured the depth and diameter of 537 craters located poleward of 45°N, evaluated the slopes of the northern and southern walls of 30 PDCs, and assessed the floor roughness of 94 craters, including nine PDCs. We find that the PDCs appear to have a fresher crater morphology than the non-PDCs and that the radar-bright material has no detectable influence on crater depths, wall slopes, or floor roughness. The statistical similarity of crater depth-diameter relations for the PDC and non-PDC populations places an upper limit on the thickness of the radar-bright material (<170 m for a crater 11 km in diameter) that can be refined by future detailed analysis. Results of the current study are consistent with the view that the radar-bright material constitutes a relatively thin layer emplaced preferentially in comparatively young craters.

  • variations in the abundances of potassium and thorium on the surface of mercury results from the MESSENGER gamma ray spectrometer
    Journal of Geophysical Research, 2012
    Co-Authors: Patrick N Peplowski, D J Lawrence, Larry R Nittler, T J Mccoy, Larry G Evans, B W Denevi, J W Head, E A Rhodes, A L Sprague, Sean C Solomon
    Abstract:

    [1] A technique for converting gamma-ray count rates measured by the Gamma-Ray Spectrometer on the MESSENGER Spacecraft to spatially resolved maps of the gamma-ray emission from the surface of Mercury is utilized to map the surface distributions of the elements Si, O, and K over the planet's northern hemisphere. Conversion of the K gamma-ray count rates to elemental abundances on the surface reveals variations from 300 to 2400 ppm. A comparison of these abundances with models for the maximum surface temperature suggests the possibility that a temperature-related process is controlling the K abundances on the surface as well as providing K to the exosphere. The abundances of K and Th have been determined for several geologically distinct regions, including Mercury's northern smooth plains and the plains interior to the Caloris basin. The lack of a significant variation in the measured Th abundances suggests that there may be considerable variability in the K/Th abundance ratio over the mapped regions.

  • major element abundances on the surface of mercury results from the MESSENGER gamma ray spectrometer
    Journal of Geophysical Research, 2012
    Co-Authors: Larry G Evans, Sean C Solomon, D J Lawrence, Patrick N Peplowski, Larry R Nittler, T J Mccoy, E A Rhodes, A L Sprague, K R Stockstillcahill
    Abstract:

    [1] Orbital gamma-ray measurements obtained by the MESSENGER Spacecraft have been analyzed to determine the abundances of the major elements Al, Ca, S, Fe, and Na on the surface of Mercury. The Si abundance was determined and used to normalize those of the other reported elements. The Na analysis provides the first abundance estimate of 2.9 ± 0.1 wt% for this element on Mercury's surface. The other elemental results (S/Si = 0.092 ± 0.015, Ca/Si = 0.24 ± 0.05, and Fe/Si = 0.077 ± 0.013) are consistent with those previously obtained by the MESSENGER X-Ray Spectrometer, including the high sulfur and low iron abundances. Because of different sampling depths for the two techniques, this agreement indicates that Mercury's regolith is, on average, homogenous to a depth of tens of centimeters. The elemental results from gamma-ray and X-ray spectrometry are most consistent with petrologic models suggesting that Mercury's surface is dominated by Mg-rich silicates. We also compare the results with those obtained during the MESSENGER flybys and with ground-based observations of Mercury's surface and exosphere.

  • large impact basins on mercury global distribution characteristics and modification history from MESSENGER orbital data
    Journal of Geophysical Research, 2012
    Co-Authors: Caleb I Fassett, Gregory A Neumann, Maria T Zuber, David E Smith, Sean C Solomon, J W Head, D M H Baker, C Klimczak
    Abstract:

    [1] The formation of large impact basins (diameter D ≥ 300 km) was an important process in the early geological evolution of Mercury and influenced the planet's topography, stratigraphy, and crustal structure. We catalog and characterize this basin population on Mercury from global observations by the MESSENGER Spacecraft, and we use the new data to evaluate basins suggested on the basis of the Mariner 10 flybys. Forty-six certain or probable impact basins are recognized; a few additional basins that may have been degraded to the point of ambiguity are plausible on the basis of new data but are classified as uncertain. The spatial density of large basins (D ≥ 500 km) on Mercury is lower than that on the Moon. Morphological characteristics of basins on Mercury suggest that on average they are more degraded than lunar basins. These observations are consistent with more efficient modification, degradation, and obliteration of the largest basins on Mercury than on the Moon. This distinction may be a result of differences in the basin formation process (producing fewer rings), relaxation of topography after basin formation (subduing relief), or rates of volcanism (burying basin rings and interiors) during the period of heavy bombardment on Mercury from those on the Moon.

Gregory A Neumann - One of the best experts on this subject based on the ideXlab platform.

  • calibration of the mercury laser altimeter on the MESSENGER Spacecraft
    IEEE Transactions on Geoscience and Remote Sensing, 2015
    Co-Authors: Xiaoli Sun, Gregory A Neumann
    Abstract:

    This paper gives a detailed description of the prelaunch and in-orbit calibrations of the Mercury Laser Altimeter (MLA) on the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) mission, which was launched on August 3, 2004 and has been operating in orbit about Mercury since March 2011. A brief summary of the MLA instrument is given, followed by the instrument measurement model and calibration formulas. The prelaunch tests used to determine the values of various calibration coefficients are described. The boresight alignment parameters were verified and recalibrated by special tests, with the MESSENGER Spacecraft en route to Mercury. The MLA instrument model and the calibration methods were largely derived from airborne and spaceborne lidar for Earth science observation at the NASA Goddard Space Flight Center and will benefit future space lidar developments for Earth and space science.

  • the gravity field orientation and ephemeris of mercury from MESSENGER observations after three years in orbit
    Journal of Geophysical Research, 2014
    Co-Authors: Gregory A Neumann, Maria T Zuber, E Mazarico, Antonio Genova, Sander Goossens, F G Lemoine, David E Smith
    Abstract:

    We have analyzed 3 years of radio tracking data from the MESSENGER Spacecraft in orbit around Mercury and determined the gravity field, planetary orientation, and ephemeris of the innermost planet. With improvements in spatial coverage, force modeling, and data weighting, we refined an earlier global gravity field both in quality and resolution, and we present here a spherical harmonic solution to degree and order 50. In this field, termed HgM005, uncertainties in low-degree coefficients are reduced by an order of magnitude relative to earlier global fields, and we obtained a preliminary value of the tidal Love number k2 of 0.451 ± 0.014. We also estimated Mercury's pole position, and we obtained an obliquity value of 2.06 ± 0.16 arcmin, in good agreement with analysis of Earth-based radar observations. From our updated rotation period (58.646146 ± 0.000011 days) and Mercury ephemeris, we verified experimentally the planet's 3:2 spin-orbit resonance to greater accuracy than previously possible. We present a detailed analysis of the HgM005 covariance matrix, and we describe some near-circular frozen orbits around Mercury that could be advantageous for future exploration.

  • images of surface volatiles in mercury s polar craters acquired by the MESSENGER Spacecraft
    Geology, 2014
    Co-Authors: N L Chabot, Gregory A Neumann, S L Murchie, D T Blewett, E Mazarico, C M Ernst, B W Denevi, H Nair, A N Deutsch, D A Paige
    Abstract:

    Images acquired by NASA's MESSENGER Spacecraft have revealed the morphology of frozen volatiles in Mercury's permanently shadowed polar craters and provide insight into the mode of emplacement and evolution of the polar deposits. The images show extensive, spatially continuous regions with distinctive reflectance properties. A site within Prokofiev crater identified as containing widespread surface water ice exhibits a cratered texture that resembles the neighboring sunlit surface except for its uniformly higher reflectance, indicating that the surficial ice was emplaced after formation of the underlying craters. In areas where water ice is inferred to be present but covered by a thin layer of dark, organic-rich volatile material, regions with uniformly lower reflectance extend to the edges of the shadowed areas and terminate with sharp boundaries. The sharp boundaries indicate that the volatile deposits at Mercury's poles are geologically young, relative to the time scale for lateral mixing by impacts, and either are restored at the surface through an ongoing process or were delivered to the planet recently.

  • characterization of the morphometry of impact craters hosting polar deposits in mercury s north polar region
    Journal of Geophysical Research, 2012
    Co-Authors: Matthieu J. Talpe, Gregory A Neumann, Maria T Zuber, Sean C Solomon, E Mazarico, Di Yang, F Vilas
    Abstract:

    [1] Earth-based radar images of Mercury show radar-bright material inside impact craters near the planet's poles. A previous study indicated that the polar-deposit-hosting craters (PDCs) at Mercury's north pole are shallower than craters that lack such deposits. We use data acquired by the Mercury Laser Altimeter on the MESSENGER Spacecraft during 11 months of orbital observations to revisit the depths of craters at high northern latitudes on Mercury. We measured the depth and diameter of 537 craters located poleward of 45°N, evaluated the slopes of the northern and southern walls of 30 PDCs, and assessed the floor roughness of 94 craters, including nine PDCs. We find that the PDCs appear to have a fresher crater morphology than the non-PDCs and that the radar-bright material has no detectable influence on crater depths, wall slopes, or floor roughness. The statistical similarity of crater depth-diameter relations for the PDC and non-PDC populations places an upper limit on the thickness of the radar-bright material (<170 m for a crater 11 km in diameter) that can be refined by future detailed analysis. Results of the current study are consistent with the view that the radar-bright material constitutes a relatively thin layer emplaced preferentially in comparatively young craters.

  • large impact basins on mercury global distribution characteristics and modification history from MESSENGER orbital data
    Journal of Geophysical Research, 2012
    Co-Authors: Caleb I Fassett, Gregory A Neumann, Maria T Zuber, David E Smith, Sean C Solomon, J W Head, D M H Baker, C Klimczak
    Abstract:

    [1] The formation of large impact basins (diameter D ≥ 300 km) was an important process in the early geological evolution of Mercury and influenced the planet's topography, stratigraphy, and crustal structure. We catalog and characterize this basin population on Mercury from global observations by the MESSENGER Spacecraft, and we use the new data to evaluate basins suggested on the basis of the Mariner 10 flybys. Forty-six certain or probable impact basins are recognized; a few additional basins that may have been degraded to the point of ambiguity are plausible on the basis of new data but are classified as uncertain. The spatial density of large basins (D ≥ 500 km) on Mercury is lower than that on the Moon. Morphological characteristics of basins on Mercury suggest that on average they are more degraded than lunar basins. These observations are consistent with more efficient modification, degradation, and obliteration of the largest basins on Mercury than on the Moon. This distinction may be a result of differences in the basin formation process (producing fewer rings), relaxation of topography after basin formation (subduing relief), or rates of volcanism (burying basin rings and interiors) during the period of heavy bombardment on Mercury from those on the Moon.

Maria T Zuber - One of the best experts on this subject based on the ideXlab platform.

  • Measurement of the radius of Mercury by radio occultation during the MESSENGER flybys
    2020
    Co-Authors: Mark E Perry, Maria T Zuber, David E Smith, Sean C Solomon, Olivier S. Barnouin, Roger J Phillips, Daniel S Kahan, Carolyn M Ernst, Dipak K Srinivasan, Jürgen Oberst
    Abstract:

    a b s t r a c t The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) Spacecraft completed three flybys of Mercury in [2008][2009]. During the first and third of those flybys, MESSENGER passed behind the planet from the perspective of Earth, occulting the radio-frequency (RF) transmissions. The occultation start and end times, recovered with 0.1 s accuracy or better by fitting edgediffraction patterns to the RF power history, are used to estimate Mercury's radius at the tangent point of the RF path. To relate the measured radius to the planet shape, we evaluate local topography using images to identify the high-elevation feature that defines the RF path or using altimeter data to quantify surface roughness. Radius measurements are accurate to 150 m, and uncertainty in the average radius of the surrounding terrain, after adjustments are made from the local high at the tangent point of the RF path, is 350 m. The results are consistent with Mercury's equatorial shape as inferred from observations by the Mercury Laser Altimeter and ground-based radar. The three independent estimates of radius from occultation events collectively yield a mean radius for Mercury of 2439.2 7 0.5 km

  • precession of mercury s perihelion from ranging to the MESSENGER Spacecraft
    The Astronomical Journal, 2017
    Co-Authors: R S Park, William M Folkner, Alexander S Konopliv, James G Williams, David E Smith, Maria T Zuber
    Abstract:

    The perihelion of Mercury's orbit precesses due to perturbations from other solar system bodies, solar quadrupole moment (J 2), and relativistic gravitational effects that are proportional to linear combinations of the parametrized post-Newtonian parameters β and γ. The orbits and masses of the solar system bodies are quite well known, and thus the uncertainty in recovering the precession rate of Mercury's perihelion is dominated by the uncertainties in the parameters J 2, β, and γ. Separating the effects due to these parameters is challenging since the secular precession rate has a linear dependence on each parameter. Here we use an analysis of radiometric range measurements to the MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) Spacecraft in orbit about Mercury to estimate the precession of Mercury's perihelion. We show that the MESSENGER ranging data allow us to measure not only the secular precession rate of Mercury's perihelion with substantially improved accuracy, but also the periodic perturbation in the argument of perihelion sensitive to β and γ. When combined with the γ estimate from a Shapiro delay experiment from the Cassini mission, we can decouple the effects due to β and J 2 and estimate both parameters, yielding and J 2 = (2.25 ± 0.09) × 10−7. We also estimate the total precession rate of Mercury's perihelion as 575.3100 ± 0.0015''/century and provide estimated contributions and uncertainties due to various perturbing effects.

  • the gravity field orientation and ephemeris of mercury from MESSENGER observations after three years in orbit
    Journal of Geophysical Research, 2014
    Co-Authors: Gregory A Neumann, Maria T Zuber, E Mazarico, Antonio Genova, Sander Goossens, F G Lemoine, David E Smith
    Abstract:

    We have analyzed 3 years of radio tracking data from the MESSENGER Spacecraft in orbit around Mercury and determined the gravity field, planetary orientation, and ephemeris of the innermost planet. With improvements in spatial coverage, force modeling, and data weighting, we refined an earlier global gravity field both in quality and resolution, and we present here a spherical harmonic solution to degree and order 50. In this field, termed HgM005, uncertainties in low-degree coefficients are reduced by an order of magnitude relative to earlier global fields, and we obtained a preliminary value of the tidal Love number k2 of 0.451 ± 0.014. We also estimated Mercury's pole position, and we obtained an obliquity value of 2.06 ± 0.16 arcmin, in good agreement with analysis of Earth-based radar observations. From our updated rotation period (58.646146 ± 0.000011 days) and Mercury ephemeris, we verified experimentally the planet's 3:2 spin-orbit resonance to greater accuracy than previously possible. We present a detailed analysis of the HgM005 covariance matrix, and we describe some near-circular frozen orbits around Mercury that could be advantageous for future exploration.

  • characterization of the morphometry of impact craters hosting polar deposits in mercury s north polar region
    Journal of Geophysical Research, 2012
    Co-Authors: Matthieu J. Talpe, Gregory A Neumann, Maria T Zuber, Sean C Solomon, E Mazarico, Di Yang, F Vilas
    Abstract:

    [1] Earth-based radar images of Mercury show radar-bright material inside impact craters near the planet's poles. A previous study indicated that the polar-deposit-hosting craters (PDCs) at Mercury's north pole are shallower than craters that lack such deposits. We use data acquired by the Mercury Laser Altimeter on the MESSENGER Spacecraft during 11 months of orbital observations to revisit the depths of craters at high northern latitudes on Mercury. We measured the depth and diameter of 537 craters located poleward of 45°N, evaluated the slopes of the northern and southern walls of 30 PDCs, and assessed the floor roughness of 94 craters, including nine PDCs. We find that the PDCs appear to have a fresher crater morphology than the non-PDCs and that the radar-bright material has no detectable influence on crater depths, wall slopes, or floor roughness. The statistical similarity of crater depth-diameter relations for the PDC and non-PDC populations places an upper limit on the thickness of the radar-bright material (<170 m for a crater 11 km in diameter) that can be refined by future detailed analysis. Results of the current study are consistent with the view that the radar-bright material constitutes a relatively thin layer emplaced preferentially in comparatively young craters.

  • large impact basins on mercury global distribution characteristics and modification history from MESSENGER orbital data
    Journal of Geophysical Research, 2012
    Co-Authors: Caleb I Fassett, Gregory A Neumann, Maria T Zuber, David E Smith, Sean C Solomon, J W Head, D M H Baker, C Klimczak
    Abstract:

    [1] The formation of large impact basins (diameter D ≥ 300 km) was an important process in the early geological evolution of Mercury and influenced the planet's topography, stratigraphy, and crustal structure. We catalog and characterize this basin population on Mercury from global observations by the MESSENGER Spacecraft, and we use the new data to evaluate basins suggested on the basis of the Mariner 10 flybys. Forty-six certain or probable impact basins are recognized; a few additional basins that may have been degraded to the point of ambiguity are plausible on the basis of new data but are classified as uncertain. The spatial density of large basins (D ≥ 500 km) on Mercury is lower than that on the Moon. Morphological characteristics of basins on Mercury suggest that on average they are more degraded than lunar basins. These observations are consistent with more efficient modification, degradation, and obliteration of the largest basins on Mercury than on the Moon. This distinction may be a result of differences in the basin formation process (producing fewer rings), relaxation of topography after basin formation (subduing relief), or rates of volcanism (burying basin rings and interiors) during the period of heavy bombardment on Mercury from those on the Moon.

David E Smith - One of the best experts on this subject based on the ideXlab platform.

  • Measurement of the radius of Mercury by radio occultation during the MESSENGER flybys
    2020
    Co-Authors: Mark E Perry, Maria T Zuber, David E Smith, Sean C Solomon, Olivier S. Barnouin, Roger J Phillips, Daniel S Kahan, Carolyn M Ernst, Dipak K Srinivasan, Jürgen Oberst
    Abstract:

    a b s t r a c t The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) Spacecraft completed three flybys of Mercury in [2008][2009]. During the first and third of those flybys, MESSENGER passed behind the planet from the perspective of Earth, occulting the radio-frequency (RF) transmissions. The occultation start and end times, recovered with 0.1 s accuracy or better by fitting edgediffraction patterns to the RF power history, are used to estimate Mercury's radius at the tangent point of the RF path. To relate the measured radius to the planet shape, we evaluate local topography using images to identify the high-elevation feature that defines the RF path or using altimeter data to quantify surface roughness. Radius measurements are accurate to 150 m, and uncertainty in the average radius of the surrounding terrain, after adjustments are made from the local high at the tangent point of the RF path, is 350 m. The results are consistent with Mercury's equatorial shape as inferred from observations by the Mercury Laser Altimeter and ground-based radar. The three independent estimates of radius from occultation events collectively yield a mean radius for Mercury of 2439.2 7 0.5 km

  • precession of mercury s perihelion from ranging to the MESSENGER Spacecraft
    The Astronomical Journal, 2017
    Co-Authors: R S Park, William M Folkner, Alexander S Konopliv, James G Williams, David E Smith, Maria T Zuber
    Abstract:

    The perihelion of Mercury's orbit precesses due to perturbations from other solar system bodies, solar quadrupole moment (J 2), and relativistic gravitational effects that are proportional to linear combinations of the parametrized post-Newtonian parameters β and γ. The orbits and masses of the solar system bodies are quite well known, and thus the uncertainty in recovering the precession rate of Mercury's perihelion is dominated by the uncertainties in the parameters J 2, β, and γ. Separating the effects due to these parameters is challenging since the secular precession rate has a linear dependence on each parameter. Here we use an analysis of radiometric range measurements to the MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) Spacecraft in orbit about Mercury to estimate the precession of Mercury's perihelion. We show that the MESSENGER ranging data allow us to measure not only the secular precession rate of Mercury's perihelion with substantially improved accuracy, but also the periodic perturbation in the argument of perihelion sensitive to β and γ. When combined with the γ estimate from a Shapiro delay experiment from the Cassini mission, we can decouple the effects due to β and J 2 and estimate both parameters, yielding and J 2 = (2.25 ± 0.09) × 10−7. We also estimate the total precession rate of Mercury's perihelion as 575.3100 ± 0.0015''/century and provide estimated contributions and uncertainties due to various perturbing effects.

  • the gravity field orientation and ephemeris of mercury from MESSENGER observations after three years in orbit
    Journal of Geophysical Research, 2014
    Co-Authors: Gregory A Neumann, Maria T Zuber, E Mazarico, Antonio Genova, Sander Goossens, F G Lemoine, David E Smith
    Abstract:

    We have analyzed 3 years of radio tracking data from the MESSENGER Spacecraft in orbit around Mercury and determined the gravity field, planetary orientation, and ephemeris of the innermost planet. With improvements in spatial coverage, force modeling, and data weighting, we refined an earlier global gravity field both in quality and resolution, and we present here a spherical harmonic solution to degree and order 50. In this field, termed HgM005, uncertainties in low-degree coefficients are reduced by an order of magnitude relative to earlier global fields, and we obtained a preliminary value of the tidal Love number k2 of 0.451 ± 0.014. We also estimated Mercury's pole position, and we obtained an obliquity value of 2.06 ± 0.16 arcmin, in good agreement with analysis of Earth-based radar observations. From our updated rotation period (58.646146 ± 0.000011 days) and Mercury ephemeris, we verified experimentally the planet's 3:2 spin-orbit resonance to greater accuracy than previously possible. We present a detailed analysis of the HgM005 covariance matrix, and we describe some near-circular frozen orbits around Mercury that could be advantageous for future exploration.

  • large impact basins on mercury global distribution characteristics and modification history from MESSENGER orbital data
    Journal of Geophysical Research, 2012
    Co-Authors: Caleb I Fassett, Gregory A Neumann, Maria T Zuber, David E Smith, Sean C Solomon, J W Head, D M H Baker, C Klimczak
    Abstract:

    [1] The formation of large impact basins (diameter D ≥ 300 km) was an important process in the early geological evolution of Mercury and influenced the planet's topography, stratigraphy, and crustal structure. We catalog and characterize this basin population on Mercury from global observations by the MESSENGER Spacecraft, and we use the new data to evaluate basins suggested on the basis of the Mariner 10 flybys. Forty-six certain or probable impact basins are recognized; a few additional basins that may have been degraded to the point of ambiguity are plausible on the basis of new data but are classified as uncertain. The spatial density of large basins (D ≥ 500 km) on Mercury is lower than that on the Moon. Morphological characteristics of basins on Mercury suggest that on average they are more degraded than lunar basins. These observations are consistent with more efficient modification, degradation, and obliteration of the largest basins on Mercury than on the Moon. This distinction may be a result of differences in the basin formation process (producing fewer rings), relaxation of topography after basin formation (subduing relief), or rates of volcanism (burying basin rings and interiors) during the period of heavy bombardment on Mercury from those on the Moon.

  • the morphology of craters on mercury results from MESSENGER flybys
    Icarus, 2012
    Co-Authors: O S Barnouin, Gregory A Neumann, Maria T Zuber, David E Smith, S L Murchie, Robert R Herrick, John E Chappelow, L M Prockter
    Abstract:

    Topographic data measured from the Mercury Laser Altimeter (MLA) and the Mercury Dual Imaging System (MDIS) aboard the MESSENGER Spacecraft were used for investigations of the relationship between depth and diameter for impact craters on Mercury. Results using data from the MESSENGER flybys of the innermost planet indicate that most of the craters measured with MLA are shallower than those previously measured by using Mariner 10 images. MDIS images of these same MLA-measured craters show that they have been modified. The use of shadow measurement techniques, which were found to be accurate relative to the MLA results, indicate that both small bowl-shaped and large complex craters that are fresh possess depth-to-diameter ratios that are in good agreement with those measured from Mariner 10 images. The preliminary data also show that the depths of modified craters are shallower relative to fresh ones, and might provide quantitative estimates of crater in-filling by subsequent volcanic or impact processes. The diameter that defines the transition from simple to complex craters on Mercury based on MESSENGER data is consistent with that reported from Mariner 10 data.

J A Slavin - One of the best experts on this subject based on the ideXlab platform.

  • a transient enhancement of mercury s exosphere at extremely high altitudes inferred from pickup ions
    Nature Communications, 2020
    Co-Authors: J M Jasinski, Daniel J. Gershman, T. A. Cassidy, Leonardo Regoli, R M Dewey, Jim M Raines, J A Slavin, A J Coates, Tom A Nordheim, Neil Murphy
    Abstract:

    Mercury has a global dayside exosphere, with measured densities of 10−2 cm−3 at ~1500 km. Here we report on the inferred enhancement of neutral densities (<102 cm−3) at high altitudes (~5300 km) by the MESSENGER Spacecraft. Such high-altitude densities cannot be accounted for by the typical exosphere. This event was observed by the Fast-Imaging Plasma Spectrometer (FIPS), which detected heavy ions of planetary origin that were recently ionized, and “picked up” by the solar wind. We estimate that the neutral density required to produce the observed pickup ion fluxes is similar to typical exospheric densities found at ~700 km altitudes. We suggest that this event was most likely caused by a meteroid impact. Understanding meteoroid impacts is critical to understanding the source processes of the exosphere at Mercury, and the use of plasma spectrometers will be crucial for future observations with the Bepi-Colombo mission. Mercury has a global dayside exosphere that is very tenuous and does not extend far from the planet. Here, the authors show enhancement of neutral densities at high altitudes inferred from pickup ions that is most likely caused by the impact of a meteroid.

  • a transient enhancement of mercury s exosphere at extremely high altitudes inferred from pickup ions
    Nature Communications, 2020
    Co-Authors: J M Jasinski, Daniel J. Gershman, T. A. Cassidy, Leonardo Regoli, R M Dewey, Jim M Raines, J A Slavin, A J Coates, Tom A Nordheim, Neil Murphy
    Abstract:

    Mercury has a global dayside exosphere, with measured densities of 10-2 cm-3 at ~1500 km. Here we report on the inferred enhancement of neutral densities (<102 cm-3) at high altitudes (~5300 km) by the MESSENGER Spacecraft. Such high-altitude densities cannot be accounted for by the typical exosphere. This event was observed by the Fast-Imaging Plasma Spectrometer (FIPS), which detected heavy ions of planetary origin that were recently ionized, and "picked up" by the solar wind. We estimate that the neutral density required to produce the observed pickup ion fluxes is similar to typical exospheric densities found at ~700 km altitudes. We suggest that this event was most likely caused by a meteroid impact. Understanding meteoroid impacts is critical to understanding the source processes of the exosphere at Mercury, and the use of plasma spectrometers will be crucial for future observations with the Bepi-Colombo mission.

  • mercury s surface magnetic field determined from proton reflection magnetometry
    Geophysical Research Letters, 2014
    Co-Authors: R M Winslow, B J Anderson, Daniel J. Gershman, C. L. Johnson, Jim M Raines, Robert Lillis, H Korth, J A Slavin
    Abstract:

    Solar wind protons observed by the MESSENGER Spacecraft in orbit about Mercury exhibit signatures of precipitation loss to Mercury's surface. We apply proton-reflection magnetometry to sense Mercury's surface magnetic field intensity in the planet's northern and southern hemispheres. The results are consistent with a dipole field offset to the north and show that the technique may be used to resolve regional-scale fields at the surface. The proton loss cones indicate persistent ion precipitation to the surface in the northern magnetospheric cusp region and in the southern hemisphere at low nightside latitudes. The latter observation implies that most of the surface in Mercury's southern hemisphere is continuously bombarded by plasma, in contrast with the premise that the global magnetic field largely protects the planetary surface from the solar wind.

  • upstream ultra low frequency waves in mercury s foreshock region MESSENGER magnetic field observations
    Journal of Geophysical Research, 2013
    Co-Authors: B J Anderson, J A Slavin, S A Boardsen, P J Chi, X Blancocano, H Korth
    Abstract:

    [1] Mercury's bow shock is unique in our solar system as it is produced by low Mach number solar wind blowing over a small magnetized body. The availability of MESSENGER orbiter data enables us for the first time to conduct an in-depth study of upstream waves in Mercury's foreshock. This paper reports first results of an observational study of upstream ULF waves in Mercury's foreshock using high-time resolution magnetic field data from the MESSENGER Spacecraft to understand the general morphology of these waves. We find that the most common wave phenomenon in Mercury's foreshock has frequencies ~ 2 Hz, with properties similar to the 1 Hz whistler waves in the Earth's foreshock. Their generation appears to be generic to the shock and not affected by the weak strength and small size of Mercury's bow shock. On the other hand, the most common wave phenomenon in the Earth's foreshock is the large-amplitude 30 second waves, identified as fast magnetosonic waves generated by backstreaming ions. Similar waves at Mercury have wave frequencies at ~ 0.3 Hz, but occur only sporadically. The general lack of strong “30 second” magnetosonic waves at Mercury can be attributed to the lack of strong backstreaming ions due to a weak bow shock and not enough time for wave growth due to the small foreshock size. Superposed on the “1 Hz” whistler waves, there are short bursts of spectral peaks at ~ 0.8 Hz that are new and have not been reported previously in Mariner 10 data.

  • kinetic scale magnetic turbulence and finite larmor radius effects at mercury
    Journal of Geophysical Research, 2011
    Co-Authors: B J Anderson, J A Slavin, S A Boardsen, Vadim M Uritsky, G V Khazanov, E Donovan, Haje Korth
    Abstract:

    [1] We use a nonstationary generalization of the higher-order structure function technique to investigate statistical properties of the magnetic field fluctuations recorded by MESSENGER Spacecraft during its first flyby (01/14/2008) through the near-Mercury space environment, with the emphasis on key boundary regions participating in the solar wind – magnetosphere interaction. Our analysis shows, for the first time, that kinetic-scale fluctuations play a significant role in the Mercury's magnetosphere up to the largest resolvable timescale (∼20 s) imposed by the signal nonstationarity, suggesting that turbulence at this planet is largely controlled by finite Larmor radius effects. In particular, we report the presence of a highly turbulent and extended foreshock system filled with packets of ULF oscillations, broad-band intermittent fluctuations in the magnetosheath, ion-kinetic turbulence in the central plasma sheet of Mercury's magnetotail, and kinetic-scale fluctuations in the inner current sheet encountered at the outbound (dawn-side) magnetopause. Overall, our measurements indicate that the Hermean magnetosphere, as well as the surrounding region, are strongly affected by non-MHD effects introduced by finite sizes of cyclotron orbits of the constituting ion species. Physical mechanisms of these effects and their potentially critical impact on the structure and dynamics of Mercury's magnetic field remain to be understood.