Detection of solar wind-produced water in irradiated rims on silicate minerals
John P. Bradley et al.
Significance
Whether water is produced by solar wind (SW) radiolysis has been debated for more than four decades. In this paper, we exploit the high spatial resolution of electron microscopy and sensitivity of valence electron energy-loss spectroscopy to detect water (liquid or vapor) in vesicles within (SW-produced) space-weathered rims on interplanetary dust particle (IDP) surfaces. Water in the rims has implications for the origin of water on airless bodies like the Moon and asteroids, the delivery of water to the surfaces of terrestrial planets, and the production of water in other astrophysical environments. In particular, water and organic carbon were likely delivered simultaneously by the high flux of IDPs accreted by the early Earth and other terrestrial planets.
Abstract
The solar wind (SW), composed of predominantly ∼1-keV H+ ions, produces amorphous rims up to ∼150 nm thick on the surfaces of minerals exposed in space. Silicates with amorphous rims are observed on interplanetary dust particles and on lunar and asteroid soil regolith grains. Implanted H+ may react with oxygen in the minerals to form trace amounts of hydroxyl (−OH) and/or water (H2O). Previous studies have detected hydroxyl in lunar soils, but its chemical state, physical location in the soils, and source(s) are debated. If −OH or H2O is generated in rims on silicate grains, there are important implications for the origins of water in the solar system and other astrophysical environments. By exploiting the high spatial resolution of transmission electron microscopy and valence electron energy-loss spectroscopy, we detect water sealed in vesicles within amorphous rims produced by SW irradiation of silicate mineral grains on the exterior surfaces of interplanetary dust particles. Our findings establish that water is a byproduct of SW space weathering. We conclude, on the basis of the pervasiveness of the SW and silicate materials, that the production of radiolytic SW water on airless bodies is a ubiquitous process throughout the solar system.solar wind radiolysis prebiotic watercosmic dust astrobiology aberration-corrected scanning transmission electron microscopy
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Footnotes
↵1To whom correspondence should be addressed. E-mail: johnbrad@hawaii.edu
Author contributions: J.P.B., M.H.N., H.A.B., and M.C.M. performed research; H.A.I., J.J.G.-D., J.C., H.A.B., and M.C.M. analyzed data; and J.P.B., H.A.I., J.J.G.-D., J.C., and M.H.N. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.*Topanni A, Dukes C, Baragiola R, Bradley JP (2006) 37th Lunar Planet Sci Conf, March 13–17, 2006, League City, TX, abstr. 2056.†Daulton TL, Bernatowicz TJ, Croat TK (2012) 43rd Lunar Planet Sci Conf, March 19–23, 2012, The Woodlands, TX, abstr. 2247.
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1320115111/-/DCSupplemental.
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