[IGPP Everyone] [EPSS Everyone] Planetary Science Seminar: TODAY

[Kevin McKeegan]

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*PLANETARY SCIENCE SEMINAR*

*Thursday, May 24*

*noon in Slichter 3853*

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*  Mathieu Choukroun*

*Jet Propulsion Laboratory*



*“Clathrate hydrates, ammonia, and interior-atmosphere exchanges on Titan”*

--
Titan is the largest moon of Saturn (2,575 km diameter) and possesses a
dense atmosphere that
exhibits a rich organic photochemistry: solar UV photons dissociate methane
CH4 and nitrogen
N2 in the upper atmosphere, which recombine to form increasingly complex
molecules. Methane
is a critical fuel for Titan’s hydrocarbon cycle but the present-day
amounts of CH4 in Titan’s
atmosphere would be entirely depleted in a few tens to 100 Myr, and the
atmospheric chemical
engine would stop. Although it is possible that we currently witness a
unique moment of Titan’s
history, the large amounts of complex organic materials present in the
equatorial dunes and
elsewhere on the surface suggest that the hydrocarbon cycle is a
long-lasting feature of Titan.
Therefore, geologic processes likely contribute to the replenishment of
methane in the
atmosphere.

Methane clathrate hydrates have long been inferred to act as volatile
reservoirs on Titan, whose
dissociation could contribute to methane outgassing. However, experimental
studies showed that
pure methane clathrates can exist throughout Titan’s interior and on the
surface. Therefore, the
effect of antifreeze / clathrate inhibitor molecules such as ammonia NH3
needs to be better
understood. Over the past few years, we have conducted several experimental
studies in the
H2O-NH3-THF system to decipher the effect of ammonia on the phase behavior
of clathrate
hydrates, assorted with thermal modeling of Titan’s subsurface, in order to
unravel the processes
through which clathrates may destabilize and release methane in Titan’s
atmosphere. We will
present results to date and their implications for Titan’s hydrocarbon
cycle.

--
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Kevin D. McKeegan
Professor of Cosmochemistry & Geochemistry
Dept. of Earth, Planetary, and Space Sciences
UCLA
Los Angeles, CA 90095-1567
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mckeegan at epss.ucla.edu
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