Cahill, J. T. S. | Search NASA

NASA NTRS2017

Investigating Evolved Compositions Around Wolf Crater

Wolf crater is an irregularly shaped, approximately 25 km crater in the south-central portion of Mare Nubium on the lunar nearside. While not previously identified as a lunar "red spot", Wolf crater was identified as a Th anomaly by Lawrence and coworkers. We have used data from the Lunar Reconnaissance Orbiter (LRO) to determine the area surrounding Wolf crater has composition more similar to highly evolved, non-mare volcanic structures than typical lunar crustal lithology. In this presentation, we will investigate the geomorphology and composition of the Wolf crater and discuss implications for the origin of the anomalous terrain.

Greenhagen, B. T.↗

NASA NTRS2016

Bistatic Radar Observations of the Moon Using Mini-RF on LRO and the Arecibo Observatory

The Miniature Radio Frequency (Mini-RF) instrument aboard NASA's Lunar Reconnaissance Orbiter (LRO) is a hybrid dual-polarized synthetic aperture radar (SAR) that operated in concert with the Arecibo Observatory to collect bistatic radar data of the lunar nearside from 2012 to 2015. The purpose of this bistatic campaign was to characterize the radar scattering properties of the surface and near-surface, as a function of bistatic angle, for a variety of lunar terrains and search for a coherent backscatter opposition effect indicative of the presence of water ice. A variety of lunar terrain types were sampled over a range of incidence and bistatic angles; including mare, highland, pyroclastic, crater ejecta, and crater floor materials. Responses consistent with an opposition effect were observed for the ejecta of several Copernican-aged craters and the floor of the south-polar crater Cabeus. The responses of ejecta material varied by crater in a manner that suggests a relationship with crater age. The response for Cabeus was observed within the portion of its floor that is not in permanent shadow. The character of the response differs from that of crater ejecta and appears unique with respect to all other lunar terrains observed. Analysis of data for this region suggests that the unique nature of the response may indicate the presence of near-surface deposits of water ice.

Patterson, G. W.↗

NASA NTRS2016

Modeling Magnetite Reflectance Spectra Using Hapke Theory and Existing Optical Constants

Magnetite is an accessory mineral found in terrestrial environments, some meteorites, and the lunar surface. The reflectance of magnetite powers is relatively low [1], and this property makes it an analog for other dark Fe- or Ti-bearing components, particularly ilmenite on the lunar surface. The real and imaginary indices of refraction (optical constants) for magnetite are available in the literature [2-3], and online [4]. Here we use these values to calculate the reflectance of particulates and compare these model spectra to reflectance measurements of magnetite available on-line [5].

terrestrial environments↗

NASA NTRS2013

Evidence for Water Ie on the Moon: Results for Anomalous Polar Craters from the LRO Mini-RF Imaging Radar

The Mini-RF radar instrument on the Lunar Reconnaissance Orbiter spacecraft mapped both lunar poles in two different RF wavelengths (complete mapping at 12.6 cm S-band and partial mapping at 4.2 cm X-band) in two look directions, removing much of the ambiguity of previous Earth- and spacecraft-based radar mapping of the Moon's polar regions. The poles are typical highland terrain, showing expected values of radar cross section (albedo) and circular polarization ratio (CPR). Most fresh craters display high values of CPR in and outside the crater rim; the pattern of these CPR distributions is consistent with high levels of wavelength-scale surface roughness associated with the presence of block fields, impact melt flows, and fallback breccia. A different class of polar crater exhibits high CPR only in their interiors, interiors that are both permanently dark and very cold (less than 100 K). Application of scattering models developed previously suggests that these anomalously high-CPR deposits exhibit behavior consistent with the presence of water ice. If this interpretation is correct, then both poles may contain several hundred million tons of water in the form of relatively "clean" ice, all within the upper couple of meters of the lunar surface. The existence of significant water ice deposits enables both long-term human habitation of the Moon and the creation of a permanent cislunar space transportation system based upon the harvest and use of lunar propellant.

polar↗

NASA NTRS2013

Evidence for Water Ice on the Moon: Results for Anomalous Polar Craters from the LRO Mini-RF Imaging Radar

The Mini-RF radar instrument on the Lunar Reconnaissance Orbiter spacecraft mapped both lunar poles in two different RF wavelengths (complete mapping at 12.6 cm S-band and partial mapping at 4.2 cm X-band) in two look directions, removing much of the ambiguity of previous Earth- and spacecraft-based radar mapping of the Moon's polar regions. The poles are typical highland terrain, showing expected values of radar cross section (albedo) and circular polarization ratio (CPR). Most fresh craters display high values of CPR in and outside the crater rim; the pattern of these CPR distributions is consistent with high levels of wavelength-scale surface roughness associated with the presence of block fields, impact melt flows, and fallback breccia. A different class of polar crater exhibits high CPR only in their interiors, interiors that are both permanently dark and very cold (less than 100 K). Application of scattering models developed previously suggests that these anomalously high-CPR deposits exhibit behavior consistent with the presence of water ice. If this interpretation is correct, then both poles may contain several hundred million tons of water in the form of relatively "clean" ice, all within the upper couple of meters of the lunar surface. The existence of significant water ice deposits enables both long-term human habitation of the Moon and the creation of a permanent cislunar space transportation system based upon the harvest and use of lunar propellant.

Mini-RF radar↗