Physics
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufm.p13d1692g&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #P13D-1692
Physics
[5420] Planetary Sciences: Solid Surface Planets / Impact Phenomena, Cratering, [5464] Planetary Sciences: Solid Surface Planets / Remote Sensing, [6250] Planetary Sciences: Solar System Objects / Moon
Scientific paper
We present an investigation of the thickness of regolith covering lunar impact ejecta using LRO Diviner thermal infrared and both Earth-based and orbital radar observations. Blocky continuous ejecta associated with fresh impact craters show elevated values of radar circular polarization ratio (CPR) in observations acquired at a range of wavelengths. By contrast, many of these craters lack a corresponding enhancement in either calculated rock concentration or rock-free regolith temperature derived from Diviner observations, rendering their ejecta blankets thermally indistinguishable from the background regolith. The radar datasets are sensitive to rocks larger than ~1/10 the wavelength both on the surface and within the upper ~10 wavelengths of regolith, whereas the low-density, low-thermal conductivity upper regolith materials effectively shield rocks from Diviner at thicknesses on the mm- to cm-scale. Therefore, we interpret our observations as evidence that many craters' ejecta are covered by thermally insulating regolith material. In this work, we seek to constrain the thickness of this cover using Earth-based radar observations at 70-cm and 12.6-cm wavelengths, LRO Mini-RF radar observations at 12.6-cm wavelength, Diviner observations, and the results of one-dimensional analytical thermal models. As endmember cases, we investigate both mare and highlands craters whose ejecta are completely thermally insulated, and craters with exposed ejecta blocks, the latter of which show enhancements in calculated rock abundance and soil temperature that are broadly consistent with radar CPR enhancements. We also examine intermediate examples, for which enhancements in rock abundance and regolith temperature exist but are spatially limited relative to the regions of elevated radar CPR. The results of this work shed light on the mechanism(s) and rate of lunar regolith development.
Allen Christine
Bandfield Joshua L.
Campbell Bruce A.
Carter Lynn Marie
Ghent Rebecca R.
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