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Titan under a red giant sun: A new kind of “habitable” moon

1997; American Geophysical Union; Volume: 24; Issue: 22 Linguagem: Inglês

10.1029/97gl52843

1944-8007

R. D. Lorenz, J. I. Lunine, Christopher P. McKay,

Planetary Science and Exploration

We explore the response of Titan's surface and massive atmosphere to the change in solar spectrum and intensity as the sun evolves into a red giant. Titan's surface temperature is insensitive to insolation increases as the haze‐laden atmosphere “puffs up” and blocks more sunlight. However, we find a window of several hundred Myr exists, roughly 6 Gyr from now, when liquid water‐ammonia can form oceans on the surface and react with the abundant organic compounds there. The window opens due to a drop in haze production as the ultraviolet flux from the reddening sun plummets. The duration of such a window exceeds the time necessary for life to have begun on Earth. Similar environments, with ∼200K water‐ammonia oceans warmed by methane greenhouses under red stars, are an alternative to the ∼300K water‐CO 2 environments considered the classic “habitable” planet.