T166 Apollo 17 Forty-Five Years on: Reanalysis of the Geochemistry, Geophysics, and Field Geology in Light of Data from the Lunar Reconnaissance Orbiter and Other Recent Missions

Tuesday, 6 November 2018
8:00 AM - 12:00 PM
Room 236-237

HOW THE MEDIAN S-BAND CIRCULAR POLARIZATION RATIO OF KILOMETER-SCALE CRATERS EVOLVES WITH TIME ON THE LUNAR MARIA

Paper number: T166-1
Program: Technical Sessions
Time: 8:00 AM – 8:15 AM

Authors

Abstract

Measurements from the Miniature Radio Frequency (Mini-RF) instrument provide useful data for evaluating how the surface properties of lunar craters evolve with time. In particular, S-band circular polarization ratio (CPR) measurements are sensitive to the rockiness of the uppermost meter of regolith and/or roughness of surface topography around craters. We extracted radial CPR profiles from 6,241 craters in the 800 m-2 km diameter range on the lunar maria, and used pre-existing estimates for the age of these craters to construct median profiles of 14 different age classes. Although the CPR profiles for individual craters of a given age vary significantly, in aggregate, craters show a clear and systematic evolution of CPR with time. Fresh craters (<200 Ma) have ejecta with elevated CPR out to distances of more than three crater diameters beyond their rims. The extent and magnitude of this enhanced CPR in craters’ ejecta fades relatively rapidly as craters age. Within crater interiors, the CPR signature increases for 400-600 Myr and then declines. This suggests that crater interiors initially becomes rockier or rougher at centimeter-to-decimeter as regolith develops after crater formation. Additionally, our results illustrate that crater interiors and ejecta have CPR evolution that is significantly decoupled. The CPR enhancement in crater ejecta fades faster than in crater interiors. This has potential implications for understanding so-called “anomalous” craters at the lunar poles that have raised CPR in their interior compared to their ejecta and have been used to infer the presence of water ice.

Geological Society of America Abstracts with Programs. Vol. 50, No. 6

doi: 10.1130/abs/2018AM-320385

© Copyright 2018 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.