PerspectivePlanetary Science

Sampling the Moon's atmosphere

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Science  15 Jan 2016:
Vol. 351, Issue 6270, pp. 230-231
DOI: 10.1126/science.aad8245

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In H. G. Wells' 1901 science fiction classic The First Men in the Moon, two protagonists, English businessman Mr. Bedford and the eccentric physicist Dr. Cavor, knock back a special enervating concoction designed to expand their lungs, followed by the requisite fortifying brandy, before venturing onto the Moon's surface to breathe the rarefied lunar atmosphere. Even more tenuous than Wells' imagined environment, the lunar exosphere is an atmosphere so thin that atoms never collide, bounded on one side by the lunar surface and extending thousands of kilometers out into space. This low-density envelope results from a balance among the influx of material from the Sun, outgassing from the Moon's interior, delivery from meteoritic bombardment, and the loss of material to space as well as recycling in the lunar surface (see the figure). The precise formula for the formation of the lunar exosphere is unknown, but recent data from orbital spacecraft are being used to delineate the relative contributions from different processes. On page 249 of this issue, Colaprete et al. (1) report measurements of sodium and potassium (Na and K) in the lunar exosphere based on observations from the Ultraviolet and Visible Spectrometer (UVS) aboard NASA's Lunar Atmosphere and Dust Environment Explorer (LADEE), which acquired continuous dayside and nightside measurements of exospheric Na and K over multiple lunar orbits.