TRANSCRIPT: Water Worlds, Desert Planets and ... Titan

One of the many questions that I wonder about is how rare Earth actually is.  Over the years, the consensus on that question has evolved somewhat from earth not being particularly special in the universe, perhaps even outright pedestrian, to earth looking increasingly special and rare with many factors playing into its habitability and ability to support the evolution of a technological species.

A new paper, link in the description below, authored by Fergus Simpson of the University of Barcelona may help shed some light on this question. This paper details an interesting prediction made by S. F. Dermott and Carl Sagan in 1995. At the time, it was thought that Saturn's moon Titan was likely to harbor hydrocarbons in liquid form. Just how much liquid would be present was open for debate and it ranged from vast oceans to Dermott and Sagan's idea that it wouldn't be anywhere near that extensive.

They predicted that if such oceans were present on Titan, its orbit would have been circularized by the action of tidal forces. That seemingly turned out to be correct, we know now that Titan's surface liquids are confined to a relatively sparse group of lakes. On the other end of the scale, we have Enceladus and Europa where there are strong indicators of deep subsurface liquid oceans, meaning that these two bodies are water worlds coated with a layer of ice with no known land.

The paper details that, statistically speaking, the division between land and ocean on a planet should be asymmetric. This implies that habitable exoplanets are either likely to either be water worlds where the surface is mostly, or entirely, covered in ocean or desert worlds where liquid water is present but scarce. Earth is the odd planet out given that we have a good amount of ocean but also lots of land.

Examples from science fiction of worlds like these would be dry, arid Tatooine from Star Wars or Thalassa from Arthur Clarke's novel "Songs of Distant Earth" which was a water world with a few human-inhabited islands, which may be the more common of the two in the universe.

While this does not preclude life arising on either water worlds or desert worlds, it does affect whether a technological civilization can arise. I've said in past videos that it would be exceedingly difficult for dolphins to master fire and smelt metal, regardless of their level of intelligence. On a water world, there may well be intelligence, but it might be locked in by its physiology perhaps awaiting direct contact with an alien species to liberate them from their world.

Now, much study of exoplanets will be needed to confirm or refute this paper, as Paul Gilster on his blog Centauri Dreams notes, we don't really yet have a complete picture of water delivery in the early solar system and that could affect the abundance of earth-like distributions of water within habitable zones.

Which brings me back to thoughts of strange Titan. It too is thought to have a subsurface very salty liquid water and ammonia ocean making it a sort of hybrid between a dry world and an ocean world. It may even harbor life, potentially several flavors of it in fact, one type on the surface, and another in the ocean. And it has another odd distinction, there will be a period 5 billion years from now where the sun will expand into a red giant. For a time during this period, its thought that Titan will be warm and become habitable and earth-like for a few hundred million years.

Will we some day retreat there to avoid the fury of the reddening sun and Earth's armageddon? Or will we be long gone and someone or something else arises on that little world? I find that future fun to ponder.

Thanks for listening! I am futurist and science fiction author John Michael Godier do check out my patreon page, link in the description below and be sure to check out my books at your favorite online book retailer and subscribe to my channel for regular, in-depth explorations into the interesting, weird and unknown aspects of this amazing universe in which we live.