Photochemistry of Methane-water Ices
Abstract
We report a study on the broadband ultraviolet photolysis of methane-water ice mixtures, at low concentrations and temperatures relevant to the icy satellites of the outer Solar System. Although the results are applicable to a variety of bodies in the Solar System, we concentrate on Enceladus, where methane mixed with water is expected to occur on the surface. The photochemistry of these mixtures is dominated by the action of hydroxyl radicals on methane and the resulting products, yielding methanol, formaldehyde, carbon monoxide and carbon dioxide. Near infrared spectra of the surface of Enceladus returned by Cassini show the presence of an absorption feature at 3.53 microns, ascribed to short chain organics. We assign this feature specifically to methanol, and suggest a photochemical origin. The photochemical oxidation observed in our experiments implies that, given sufficient exposure time, methane (or other organics) will eventually be completely oxidized to carbon dioxide. Thus the observation of organics on the surface of Enceladus suggests that the organics are likely of recent origin.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2008
- Bibcode:
- 2008AGUFM.P23B1370H
- Keywords:
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- 5422 Ices;
- 6008 Composition (1060);
- 6060 Radiation and chemistry;
- 6280 Saturnian satellites