o challenged the room with a hypothesized Titan climate history that differs strongly from the situation that holds today. He called it the Triton-Titan-Mars hypothesis, and the central conceit was: what if Titan hasn't always had a thick atmosphere? What if it used to look like Triton (with all its volatile components locked in surface ices), and some relatively recent event -- the long-term brightening of the Sun, or a large impact -- suddenly triggered Titan's methane to sublime to gas? Geophysically, the results could be quite interesting. FIrst of all, you'd have massive global methane rainfall, carving valleys everywhere.
More importantly, though, the thick atmosphere is an insulator. An airless world like Triton has surface temperatures that are much warmer at the equator than the poles, a difference of about 25 Kelvin. But Titan, with its methane blanket, has nearly constant temperature everywhere. That sudden warming of the poles would actually thin the icy crust, which would then sink as a result of isostasy. (Why that is and what isostasy is, are subjects for another blog entry; just take my word for it that warming icy crust thins it and lowers its elevation.)
So you'd suddenly have a global topographic gradient from equator to poles; all that rain, eroding bedrock and washing away sediment, would run from equator to poles, carrying sediment with it, depositing it in the polar depressions. As time went on and more and more of Titan's methane rained out, it would stop raining at the equator first, with Titan dessicating slowly from equator to pole. So you'd get highstanding, valley-carved mountains near the equator; badlands-style water-carved topography at midlatitudes; and sedimentary deposits and lakes in lowstanding poles. Another thing that would happen as the poles sank is that you'd see compressional tectonics -- faulted blocks rising -- and near the equator you'd see extensional tectonics -- pull-apart basins and mountain ranges.
Like all of Jeff's stories, there are intriguing matches between this fairly simple scenario and some puzzling qualities of Titan. However, it's also an incredibly simplistic view of the geological history of a very complicated world, something that Jeff is very ready to admit. But Ralph Lorenz, who commented on the talk, agreed that it was an intriguing and probably correct point that climate change on Titan can change its tectonics (the processes that form mountains and basins). In general, I love the convivial nature of the arguments that happen among this particular community.
So the Titan stuff has been very fun. There's already been so much more, though, from other icy worlds, and Mars of course. Sadly, nothing much from Venus; I poked my head into that session this morning to see the same people making only slightly different arguments than they had been making ten years ago. We need a new Venus mission. Venus, in fact, is another place where climate change may have had a direct effect on the nature of its geologic activity (and vice versa, of course). Maybe it's time for an interdisciplinary session on atmospheric forcing of planetary tectonics!