Disintegration of lunar samples over time: A test

1L. A. Taylor,2J. V. Hogancamp,3L. A. Watts,4S. J. Wentworth,4P. D. Archer,5R. A. Zeigler,6A. Basu
Meteoritics & Planetary Science (in Press) Links to Article [DOI: 10.1111/maps.13060]

1Department of Earth and Planetary Sciences, Planetary Geoscience Institute, University of Tennessee, Knoxville, Tennessee, USA
2Geocontrols Systems—Jacobs JETS Contract, NASA Johnson Space Center, Houston, Texas, USA
3Barrios Technology—Jacobs JETS Contract, NASA Johnson Space Center, Houston, Texas, USA
4Jacobs, NASA Johnson Space Center, Houston, Texas, USA
5Astromaterials Research and Exploration Science Division, NASA Johnson Space Center, Houston, Texas, USA
6Department of Earth and Atmospheric Sciences, Indiana University, Bloomington, Indiana, USA
Published by arrangement with John Wiley & Sons

Lunar samples provide ground-truth for all planetary exploration. Lunar soils, especially their <1 mm fraction, constitute the only primary standards for remotely sensing the composition of small airless planetary bodies. Therefore, maintaining the integrity, especially of the <1 mm fraction, takes on a much larger, big picture responsibility. A possibility has been suggested that lunar soils may disintegrate (to smaller grain sizes) if exposed to the Earth’s moist atmosphere, thus losing some of their intrinsic value to science. We have tested that possibility by multiple, independent reanalyses with three techniques (wet-sieving in water and in alcohol, and laser diffractometry) using a fresh allocation of Apollo 17 “orange soil,” 74220. Our results are very similar to each other despite repeated soaking–drying in water, and also to those originally determined in the 1970s. We have also used a laser diffractometry technique to reanalyze the grain sizes of ~50 mg splits of eight soils that were initially analyzed three to four decades ago. The results are randomly different from previous measurements, which we attribute to nonrepresentative subsampling of very small amounts from previous allocations; ~50 mg is too small for obtaining representative aliquots. The results of grain-size analyses presented and discussed in this study indicate that the integrity of the lunar soil 74220, and indeed, all lunar soils, has not been physically compromised in the last four decades.

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