Abstract
The exospheres that surround airless bodies such as the Moon are tenuous, atmosphere-like layers whose constituent particles rarely collide with one another. Some particles contained within such exospheres are the product of direct interactions between airless bodies and the space environment, and offer insights into space weathering processes. NASA’s Lunar Atmosphere and Dust Environment Explorer (LADEE) mission studied the Moon’s exospheric constituents in situ and detected a permanent dust exosphere1 of particles with radii as small as 300 nm. Here we present evidence from LADEE spectral data for an additional fluctuating nanodust exosphere at the Moon containing a population of particles sufficiently dense to be detectable via scattered sunlight. We compare two anti-Sun spectral observations: one near the peak of the Quadrantid meteoroid stream, the other during a period of comparatively weak stream activity. The former shows a negative spectral slope consistent with backscattering of sunlight by nanodust grains with radii less than 20 to 30 nm; the latter has a flatter spectral slope. We hypothesize that a spatially and temporally variable nanodust exosphere may exist at the Moon, and that it is modulated by changes in meteoroid impact rates, such as during encounters with meteoroid streams. The findings suggest that similar nanodust exospheres—and the particle ejection and transport processes that form them—may occur at other airless bodies.
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Acknowledgements
LADEE UVS was supported through the NASA Lunar Quest Program. The authors also acknowledge financial support from the LADEE Guest Observer Program and NASA’s Science Mission Directorate.
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D.H.W. and A.M.C. performed the analysis of the mission data. D.A.G. performed dust grain simulations and derived column abundances. T.J.S. modelled the ejecta cloud and nanodust dynamics for results interpretation. A.C. is the UVS instrument PI, and designed the measurements. All authors co-wrote the paper.
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Wooden, D., Cook, A., Colaprete, A. et al. Evidence for a dynamic nanodust cloud enveloping the Moon. Nature Geosci 9, 665–668 (2016). https://doi.org/10.1038/ngeo2779
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DOI: https://doi.org/10.1038/ngeo2779
