Joshua Sokol has published an article in NewScientist (13 August 2016, paywall) on potential ocean life in the solar system. I found a sidebar on the nature of life on Saturn’s moon Titan to be particularly interesting.
NASA/JPL-Caltech/University of Arizona/University of Idaho
Astrobiologists have speculated that any life there might run on an entirely alien chemistry. Some suggest that microbes could make a living by breathing hydrogen and eating organic molecules like acetylene and ethane. The Cassini probe has spied evidence of chemical activity in Titan’s atmosphere that seems consistent with the idea.
There could, of course, be non-biological explanations for this activity, but the only way to know what causes it is to visit Titan. No such mission has yet been signed off, but recent work has given us fresh impetus by suggesting that the moon’s ice-cold chemistry would offer the toolkit required to make weird analogues of the molecules that support life on Earth.
In 2015, a team at Cornell University in Ithaca, New York, constructed a flexible, cell-membrane-like structure using only the ingredients and conditions available on Titan. Earlier this year, Martin Rahm, also at Cornell, and colleagues did some modelling to show that Titan should possess the chemicals required to create even more complex molecules.
Hydrogen cyanide is abundant in Titan’s atmosphere and should rain down on the surface, but it doesn’t appear to build up there. Instead, Rahm suggests, hydrogen cyanide combines with other molecules when it lands, forming larger ones made of carbon, nitrogen and hydrogen called polyimines – and these could form the backbone of an alternative biology.
At terrestrial temperatures, these chemical structures would fall apart. In the cryogenic seas of Titan, however, they would be preserved and could take on a wide array of forms, some of which could carry out primitive versions of the reactions in living cells here on Earth. Rahm says they might even float to the surface of tidal pools as membrane-like films, or as mats of stacked, crystalline molecules.
Trying to visualize an entire ecology built along these lines, at the low temperatures present on Titan, leaves me breathless.
