Directly testing the distribution of surficial hydroxyl/water on the Moon with the Lunar Trailblazer mission
Abstract
In 2009, surficial hydroxyl and potentially water were detected on the lunar surface by near-infrared (NIR) spectrometers on the Chandrayaan-1, EPOXI and Cassini spacecrafts. Since that time, the distribution, abundance, and diurnal nature of the hydration has been hotly debated. The Moon Mineralogy Mapper (M3) provided the best spatially-resolved (0.54-2.98 μm; 70-280 m/pixel) coverage. However, because the majority of minerals in lunar returned samples are anhydrous, and water on the illuminated lunar surface is unstable, M3 was not optimized to rigorously quantify water abundance. The Clementine and Lunar Prospector missions had provided some indication that there might be ice in the permanently shaded regions at the poles, so the extended wavelength range of M3 to include the 3-micron water/OH band was primarily in the hopes of detecting ice at the poles, which it has now done (Li et al., 2018).
Over the last decade, different thermal corrections of the M3 data have been attempted to enable better understanding of spatial and temporal distribution of lunar surface water on sunlit terrains. However, the 3-micron cutoff wavelength for M3 results in ambiguities in the strength, shape, and position of the absorption band. Thermal emission further complicates the data, as the true temperature of the measured surface needs to be subtracted from the signal to quantify the water band depth. Discrepancies exist between results from different techniques using M3, coupled with other datasets or modeling assumptions, leading to conflicting results about whether the species is water or hydroxyl, its concentration and distribution, and whether it migrates over a lunar day. NASA recently selected the SIMPLEx smallsat Lunar Trailblazer, which will carry the High-resolution Volatiles and Minerals Moon Mapper (HVM3; 0.6-3.6 μm, similar to M3 but explicitly designed to focus on water measurements), as well as the Lunar Thermal Mapper, a thermal infrared multispectral imager to directly and simultaneously measure the temperature and rock type within each HVM3 pixel. With >1000 targeted images per instrument and the ability to peer into permanently shadow regions, Lunar Trailblazer will directly measure ice in PSRs and test hypotheses for the distribution, abundance and possible migration of water/OH on the sunlit lunar surface.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.P34B..02K
- Keywords:
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- 6205 Asteroids;
- PLANETARY SCIENCES: SOLAR SYSTEM OBJECTS;
- 6230 Martian satellites;
- PLANETARY SCIENCES: SOLAR SYSTEM OBJECTS;
- 6250 Moon;
- PLANETARY SCIENCES: SOLAR SYSTEM OBJECTS