Looking for life on Saturn's largest moon Titan may be trickier than first thought. New computer simulations suggest that if life exists, there may not be a lot of it about. In fact, the mass probably wouldn't amount to much of anything at all.
If life exists anywhere in the solar system outside of Earth, Titan sits close to the top of the list. Though it's a bit on the chilly side at -290 °F ( -179 °C), it has a thick nitrogen-rich atmosphere, lakes filled with methane and ethane, and all manner of hydrocarbons and organic aerosols that could support complex organic chemistry. In addition, there's evidence of a 300-mile-deep (483-km) subterranean ocean trapped beneath the icy crust 25 to 62 miles (40 to 100 km) thick that is warmed by hydrothermal activity caused by the tides generated by the mass of Saturn.
However, as they say, the devil is in the detail as an international team of researchers led by Antonin Affholder at the University of Arizona Department of Ecology and Evolutionary Biology and Peter Higgins at Harvard University's Department of Earth and Planetary Sciences carried out a new study that goes back to the basics.
By using computer models to simulate the likely ecology on Titan, the team came up with some surprising conclusions.
If there is life on Titan, it will be microbial and probably be pretty exotic compared to that on Earth. Though it looks as if the organic chemicals that abound on the surface should give any life there loads of food, any life on Titan would be in the subsurface world ocean. That means these organics have to get to that ocean for there to be anything to feed on them.
For purposes of the study, the simulations focused on the simple process of fermentation. Specifically, fermentation involving the organic molecule glycine, which is the simplest of all known amino acids. Fermentation is particularly attractive because it doesn't need oxygen to occur, so it probably evolved very early in the history of the Earth.
The problem the simulations found was that, though glycine or its precursors are abundant on the surface of Titan, very little of the amino acid makes it down into the buried ocean and what's there is likely due to meteor strikes creating temporary lakes that can seep through the ice.
The upshot of all this is that there isn't enough food available for the Titan microbes to feed on. As a result, if there is life on Titan, it's an astonishing small amount – as in enough to fill a typical bucket. That means that future missions to Titan will have a rough time tracking down any solitary microbes that might be wandering about.
"Our new study shows that this supply may only be sufficient to sustain a very small population of microbes weighing a total of only a few kilograms at most – equivalent to the mass of a small dog," said Affholder. "Such a tiny biosphere would average less than one cell per liter of water over Titan's entire vast ocean."
The research was published in The Planetary Science Journal.
Source: University of Arizona
