Coloration and darkening of methane clathrate and other ices by charged particle irradiation - Applications to the outer solar systemThe results of laboratory experiments simulating the irradiation of hydrocarbon-H2O or hydrocarbon-H2O/NH3 clathrates by charged particles in the outer solar system are reported. Ices produced by condensing and boiling liquid CH4 on an H2O frost surface at 100 K or by cocondensing frosts from gaseous mixtures were exposed to coronal-discharge electron irradiation at 77 K, and the spectral properties of the irradiated surfaces were determined. Significant darkening of the initially white ices was observed at doses of 1 Gerg/sq cm, corresponding to 8-500 yrs of irradiation by Uranian magnetospheric electrons on the surfaces of the principal Uranian satellites, or to total destruction of CH4 in the upper 1 mm of the satellite surfaces after 0.05-3.0 Myr. It is estimated that 10 m or more of icy satellite or comet surfaces would be radiation-hardened to a CH4-free ice-tholin mixture over 4 Gyr.
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Thompson, W. Reid (Cornell Univ. Ithaca, NY, United States)
Murray, B. G. J. P. T. (Cornell Univ. Ithaca, NY, United States)
Khare, B. N. (Cornell Univ. Ithaca, NY, United States)
Sagan, Carl (Cornell University Ithaca, NY, United States)