Episodic Collapse of Titan's Atmosphere

Details Episodic Collapse of Titan's Atmosphere Episodic Collapse of Titan's Atmosphere

Sep 1996

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996dps....28.2019l&link_type=abstract

American Astronomical Society, DPS meeting #28, #20.19; Bulletin of the American Astronomical Society, Vol. 28, p.1133

Astronomy and Astrophysics

Astronomy

Scientific paper

Titan's surface temperature of 94K is held above the effective temperature (82K) by a balance between antigreenhouse effects due to haze and methane, and stronger greenhouse opacity due to methane, hydrogen and nitrogen (McKay et al., Science 253:1118-1121, 1991). However, the present methane abundance would be depleted photochemically within a few million years unless buffered or resupplied. Further, methane photolysis is the source of both the haze and the hydrogen. Thus, if in Titan's past the methane resupply were to fail to keep up with photochemical destruction, the opacity structure of Titan's atmosphere would profoundly change. We explore these changes using a radiative-convective (R-C) model (McKay et al., Icarus 80:23-53, 1989) and find the surface temperature drops sharply as methane is depleted; so much so, indeed, that nitrogen, the dominant atmospheric constituent, becomes supersaturated. We have modified the R-C model to include a saturated, rather than convective, lower region and equate the surface pressure to the vapour pressure of nitrogen. With the present solar constant and surface albedo, temperatures of 83K are found. With a lower solar constant, lower temperatures are generated, accompanied by the condensation of several hundred millibars of nitrogen. Such significant rainout may increase the surface albedo and cause further temperature and pressure drops. This positive feedback may have culminated (perhaps many times - we are still exploring the reversibility of the collapse process) in the drop of surface pressure below 100 millibar and the onset of strong equator-to-pole temperature gradients, polar freezing and distinctly Triton-like episodes in Titan's history.

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