36th DPS Meeting, 8-12 November 2004
Session 33 Comets: Comae
Poster II, Thursday, November 11, 2004, 4:15-7:00pm, Exhibition Hall 1A

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[33.01] Cometary D/H Fractionation during Sublimation

J. R. Weirich, R. H. Brown, D. S. Lauretta (University of Arizona)

The source of water and other volatiles on the terrestrial planets has implications for the processes that occurred during the formation and evolution of the solar system (Sill and Wilkening 1978, Dreibus and Wanke 1987, Bogard et al. 2001). One proposed source of these volatiles is collisions between comets and the inner planets (Sill and Wilkening 1978, Bogard et al. 2001). However, the D/H (deuterium to hydrogen) ratio of water in cometary comas has been measured to be about twice as high as that of the Earth’s oceans (Eberhardt et al. 1995). If this ratio is representative of the bulk nucleus, then comets could not have been the source of water for Earth’s oceans.

However, if the coma is enriched in deuterium through a concentration mechanism acting at the surface of the comet, then the D/H ratio of the coma will not be representative of the D/H ratio of the bulk nucleus. In fact, we have shown through experimentation in a vacuum ice lab that during sublimation the D/H ratio of the evolved gas increases with time and eventually exceeds the initial D/H ratio of the sample. Hence, comets cannot be ruled out as the source of water on Earth. In an attempt to explain these experimental results we have been modeling diffusion dominated sublimation. Research for this project has been funded by NASA Planetary Astronomy.

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Bulletin of the American Astronomical Society, 36 #4
© 2004. The American Astronomical Soceity.