Titan Under a Red Giant Sun: A New Kind of "Habitable" Moon

Geophys Res Lett. 1997 Nov 15;24(22):2905-8. doi: 10.1029/97gl52843.


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 approximately 200K water-ammonia oceans warmed by methane greenhouses under red stars, are an alternative to the approximately 30OK water-CO2 environments considered the classic "habitable" planet.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Ammonia / analysis
  • Ammonia / chemistry
  • Atmosphere / chemistry*
  • Evolution, Planetary
  • Exobiology*
  • Extraterrestrial Environment*
  • Greenhouse Effect
  • Models, Chemical
  • Saturn*
  • Solar System
  • Sunlight*
  • Ultraviolet Rays
  • Water / chemistry


  • Water
  • Ammonia