Showing papers by "Olivier S. Barnouin published in 2013"

Bright and Dark Polar Deposits on Mercury: Evidence for Surface Volatiles

Abstract: Measurements of surface reflectance of permanently shadowed areas near Mercury’s north pole reveal regions of anomalously dark and bright deposits at 1064-nanometer wavelength. These reflectance anomalies are concentrated on poleward-facing slopes and are spatially collocated with areas of high radar backscatter postulated to be the result of near-surface water ice. Correlation of observed reflectance with modeled temperatures indicates that the optically bright regions are consistent with surface water ice, whereas dark regions are consistent with a surface layer of complex organic material that likely overlies buried ice and provides thermal insulation. Impacts of comets or volatile-rich asteroids could have provided both dark and bright deposits.

Topographic characterization of lunar complex craters

Abstract: [1] We use Lunar Orbiter Laser Altimeter topography data to revisit the depth (d)-diameter (D), and central peak height (hcp)-diameter relationships for fresh complex lunar craters. We assembled a data set of young craters with D ≥ 15 km and ensured the craters were unmodified and fresh using Lunar Reconnaissance Orbiter Wide-Angle Camera images. We used Lunar Orbiter Laser Altimeter gridded data to determine the rim-to-floor crater depths, as well as the height of the central peak above the crater floor. We established power-law d-D and hcp-D relationships for complex craters on mare and highlands terrain. Our results indicate that craters on highland terrain are, on average, deeper and have higher central peaks than craters on mare terrain. Furthermore, we find that the crater depths for both mare and highlands craters are significantly deeper than previously reported. This likely reflects the inclusion of transitional craters and/or older and/or modified craters in previous work, as well as the limitations of the stereophotogrammetric and shadow-length data sets used in those studies. There is substantial variability in the depths and the central peak heights for craters in a given diameter range. We suggest that the differences in mean d and hcp as a function of crater diameter for highlands and mare craters result from differences in bulk physical properties of the terrain types, whereas the variability in d and hcp at a given diameter may reflect variations in impactor properties and impact parameters.

Origin and flatness of ponds on asteroid 433 Eros

Abstract: NEAR-Shoemaker Multi-Spectral Imager data reveal several hundred “ponds” on 433 Eros: smooth deposits that sharply embay the bounding depressions in which they lie, and whose spectra appear blue relative to that of the surrounding terrain. We investigate the topography of these ponds on Eros using a new shape model derived from stereophotoclinometric analysis, and validated against altimetry from the NEAR Laser Rangefinder, to constrain the mode of pond formation from three existing models. We update the locations of 55 pond candidates identified in images registered to the new shape model. We classify the flatness of these features according to the behavior of the first and second derivatives of the topography. We find that less than half of pond candidates have clearly flat floors. Based on the pond topography, we favor an external origin for the ponds' deposits. We suggest that fine dust may be transported into bounding depressions by electrostatic levitation, but may adhere to slopes, and that seismic shaking may not be sufficient to bring the deposits to an equipotential surface. Disaggregation of a central boulder should result in an obvious break in slope, such a variation is only observed in roughly half the pond candidates.

Volcanic Plains in Caloris Basin: Thickness, Timing, and What Lies Beneath

Abstract: Carolyn M. Ernst, Brett W. Denevi, Scott L. Murchie, Olivier S. Barnouin, Nancy L. Chabot, James W. Head, Christian Klimczak, Gregory A. Neumann, Louise M. Prockter, Mark S. Robinson, Sean C. Solomon, and Thomas R. Watters, Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723, USA (carolyn.ernst@jhuapl.edu); Department of Geological Sciences, Brown University, Providence, RI 02912, USA; Department of Terrestrial Magnetism, Carnegie Institution of Washington, Washington, DC 20015, USA; Planetary Geodynamics Laboratory, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA; School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287, USA; Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY 10964, USA; Center for Earth and Planetary Studies, National Air and Space Museum, Smithsonian Institution, Washington, DC 20560, USA.