Saturn’s moon Titan sounds like a geological altverse with its lakes of liquid hydrocarbon, an ice crust that could be hiding a vast salty ocean, and even ghostly cryovolcanoes. Could there possibly be life hiding somewhere on this world where it’s always winter?
NASA’s Cassini spacecraft may bring scientists closer to finding out after it makes its final pass around Titan, the largest of Saturn’s 53 named moons, next month. NASA has obviously put Mars in the spotlight as a possible ancient hotbed of extraterrestrial life—but Titan vied for attention as a possibly habitable environment after discoveries made by Cassini and Huygens, its now-defunct companion probe. What the Cassini-Huygens mission revealed about Titan may change our view of life as we know it.
"Titan gives us the opportunity to search for signatures of life in multiple types of systems — familiar water-based life, but also a biological system that may have developed with hydrocarbon as a solvent," explained planetary scientist Elizabeth Turtle of the John Hopkins University Applied Physics Laboratory.
Titan is rich in all the elements that are supposed to spark life, at least in the Gaian model: carbon, hydrogen, nitrogen, oxygen, phosophorus, and sulfur. It is thought to be swimming with saltwater seas beneath its crust of ice. It also has the only other thick N2 atmosphere currently known besides that of our own planet, and is also the only other celestial body in the solar system with stable liquid (mostly methane and ethane) on its surface. Its massive hydrocarbon reserves boast more hydrocarbons than all of Earth’s combined. For any Tolkien fanatics out there (raises hand), it even has cryovolcanoes called Doom Mons and Erebor Mons. +1000 to whoever named those.
While we’re not going to find Gollum crawling around Titan’s version of the Lonely Mountain, this frozen world has a complex and unique atmospheric chemistry that produces organic materials which are then deposited on the surface. Everything that went into its lakes, seas and dune fields was originally formed in the atmosphere before they were shaped by surface winds and liquids. Even though astronomers now know the processes that affect the surface of Titan and that the surface itself is heterogeneous, their understanding of its actual chemical composition is still hazy. That makes this moon all the more enticing for exploration.
“Titan offers many examples of really interesting organic chemistry experiments with alternative structures,” noted Georgia Tech planetary scientist Britney Schmidt. "It's organic in nature, but it is not necessarily biogenic."
Astronomers now see Titan as a sort of space lab that allows them to test theories and continue studying organic processes that are prebiotic (occurring before the emergence of life) and possibly mirror those on a primordial Earth. While Titan has lakes and clouds like those we might be familiar with, it deviates from the Gaian model in that its lakes and clouds are composed mostly methane and ethane. An organic haze in its atmosphere is thought to produce prebiotic molecules. While the same sedimentary processes take place on Titan as they would on a terrestrial planet like earth, the drastically different factor is that they are playing out on a planet of ice.
Taking its cue from Titan, NASA has started planning a mission to Jupiter’s frozen moon Europa, whose icy crust is also thought to hide an alien ocean. We have already found proof that geology, chemistry and physics all apply the same way light-years from Earth. Cassini and the future Europa mission could get researchers one step closer to proving the same about that one elusive science missing from the list—biology.