Lunar Proton Albedo Anomalies: Soil, Surveyors, and Statistics

Monday, 15 December 2014
Jody Keith Wilson1, Nathan Schwadron2, Harlan E. Spence3, Anthony W Case4, Michael Joseph Golightly5, Andrew Jordan1, Mark Dixon Looper6, Noah E Petro7, Mark Southwick Robinson8, Timothy John Stubbs9, Cary J Zeitlin10, J Bernard Blake6, Justin Christophe Kasper11, Joseph E Mazur12, Sonya S Smith2 and Lawrence W Townsend13, (1)University of New Hampshire Main Campus, Space Science Center, Durham, NH, United States, (2)University of New Hampshire, Durham, NH, United States, (3)University of New Hampshire Main Campus, Durham, NH, United States, (4)Smithsonian Astrophysical Observatory, Cambridge, MA, United States, (5)Assurance Technology Corporation, Carlisle, MA, United States, (6)The Aerospace Corp, Los Angeles, CA, United States, (7)NASA GSFC, Greenbelt, MD, United States, (8)Arizona State University, Tempe, AZ, United States, (9)NASA Goddard Space Flight Center, Greenbelt, MD, United States, (10)Southwest Research Institute, Oakland, CA, United States, (11)University of Michigan, Ann Arbor, MI, United States, (12)The Aerospace Corporation, Chantilly, VA, United States, (13)University of Tennessee Knoxville, Knoxville, TN, United States
Since the launch of LRO in 2009, the CRaTER instrument has been mapping albedo protons (~100 MeV) from the Moon. These protons are produced by nuclear spallation, a consequence of galactic cosmic ray (GCR) bombardment of the lunar regolith. Just as spalled neutrons and gamma rays reveal elemental abundances in the lunar regolith, albedo protons may be a complimentary method for mapping compositional variations.

We presently find that the lunar maria have an average proton yield 0.9% ±0.3% higher than the average yield in the highlands; this is consistent with neutron data that is sensitive to the regolith’s average atomic weight.

We also see cases where two or more adjacent pixels (15° × 15°) have significantly anomalous yields above or below the mean. These include two high-yielding regions in the maria, and three low-yielding regions in the far-side highlands. Some of the regions could be artifacts of Poisson noise, but for completeness we consider possible effects from compositional anomalies in the lunar regolith, including pyroclastic flows, antipodes of fresh craters, and so-called "red spots". We also consider man-made landers and crash sites that may have brought elements not normally found in the lunar regolith.