[X] My Assistant

[Guest_AlexBlackwell_*]

From the December 15, 2006, issue of Science:

A Clathrate Reservoir Hypothesis for Enceladus' South Polar Plume
Susan W. Kieffer, Xinli Lu, Craig M. Bethke, John R. Spencer, Stephen Marshak, and Alexandra Navrotsky
Science 314, 1764-1766 (2006)
Abstract
Supporting Online Material

See also the accompanying News of the Week article "A Dry View of Enceladus Puts a Damper on Chances for Life There" by Richard Kerr.

EDIT: See also the related Space.com story.

2nd EDIT: See "Scientists propose alternate model for plume on Enceladus."

This post has been edited by AlexBlackwell: Dec 14 2006, 07:19 PM

[Guest_AlexBlackwell_*]

Matson et al. have an interesting paper in press with Icarus:

Enceladus' plume: Compositional evidence for a hot interior
Dennis L. Matson, Julie C. Castillo, Jonathan Lunine and Torrence V. Johnson
Icarus, In Press, Corrected Proof, Available online 18 December 2006
Abstract

[volcanopele]

Thanks for posting the link, Alex. I wanted to wait to comment on the Kieffer et al. paper until after that article was posted on the web. The Matson et al. article brings up I think the chief arguments for a liquid water origin of the Enceladus plumes as opposed to a clathrate origin. The key to the plume's origin is in the minor components: ammonia, propane, and acetylene. These minor components strongly suggest that the major components (water, CO2, methane, and nitrogen) have been thermally altered before they were ejected into space. Matson et al. suggest that the nitrogen in the plume originated as ammonia. At some point in Enceladus' history, the suspected water/ammonia mixture of the lower layers of the ice mantle percolated through cracks in Enceladus' rocky core, and the ammonia broke down into nitrogen. The water/ammonia mixture also would have contained CO and CO2, which when combined with water and the molecular hydrogen released from the ammonia, would have created methane. The presence of higher order hydrocarbons strongly suggest catalytic reactions, again supporting interaction between a liquid water lower mantle and hot, rocky core.

All this work again suggests that the origin of the material in Enceladus' is in a liquid lower mantle, not from clathrates in the upper mantle, as suggested by Kieffer et al.

[Guest_AlexBlackwell_*]

All this work again suggests that the origin of the material in Enceladus' is in a liquid lower mantle, not from clathrates in the upper mantle, as suggested by Kieffer et al.

Though I not an expert in this area, I have to admit the Kieffer et al. model is attractive, perhaps because it is simplistic. Having said that, maybe their model is too simplistic. As you noted, Matson et al. raise some good points, and I could well imagine that in the absence of the INMS, CAPS, and UVIS data on the plumes, one could be tempted to grab hold of the clathrate model. Many an elegant model has been slayed by those pesky little observables