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Science 25 October 1991:
Vol. 254. no. 5031, pp. 548 - 551
DOI: 10.1126/science.11538372
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Articles

Science, Vol 254, Issue 5031, 548-551
Copyright © 1991 by American Association for the Advancement of Science

articles

Clathrate hydrate formation in amorphous cometary ice analogs in vacuo

D Blake, L Allamandola, S Sandford, D Hudgins, and F Freund

Planetary Biology Branch, Ames Research Center, Moffett Field, CA 94035, USA.

The presence of clathrate hydrates in cometary ice has been suggested to account for anomalous gas release at large radial distances from the sun as well as the retention of volatiles in comets to elevated temperatures. However, how clathrate hydrates can form in low-pressure environments, such as in cold interstellar molecular clouds, in the outer reaches of the early solar nebula, or in cometary ices, has been poorly understood. Experiments performed with the use of a modified electron microscope demonstrate that during the warming of vapor-deposited amorphous ices in vacuo, clathrate hydrates can form by rearrangements in the solid state. Phase separations and microporous textures that are the result of these rearrangements may account for a variety of anomalous cometary phenomena.


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