Is there life on Titan?
Scientists looking for evidence of life on other planets in our solar system may have to expand their expectations about what counts as “life,” at least according to a new investigation of the chemical compounds present on Titan, Saturn’s largest moon.
Just like on Earth, the passing traveller to Titan would be able to witness awe-inspiring lakes, rivers and seas, but there the similarities come to a screeching halt, as average temperatures on Titan come in at about -180 degrees Celsius and those lakes and rivers turn out to be filled with liquid methane and ethane as opposed to water.
But as inhospitable as these features may seem, evidence nonetheless points to the possibility of life-enabling chemical conditions on Titan, says Martin Rahm of the Department of Chemistry and Chemical Biology at Cornell University in Ithaca, New York. “Our scientific experience is at room temperature and ambient conditions. Titan is a completely different beast,” says Rahm. “So if we think in biological terms, we’re probably going to be at a dead end.”
Instead, Rahm and his colleagues have proposed that we look for clues about the kinds of conditions that need to be present before life forms, of any kind, can take shape, and the scientists believe that Titan may just have at least some of those conditions. Specifically, when the Sun’s rays hit the nitrogen and methane-filled atmosphere on Titan, the reaction produces hydrogen cyanide, a compound deathly poisonous to you, me and everyone around here, but possibly a pre-biotic key to extraterrestrial life.
Scientists working under lab conditions have discovered that hydrogen cyanide can produce a unique compound called polyimine when combined with other molecules and this compound has the ability to exist in several different forms, depending on thermodynamic conditions. The diversity in polyimine forms leads to subtle variations in electric charge of the different forms, something that Rahm and his colleagues find as “extraordinary” on its own and also a potential game-changer in the search for life forms, if we think of how important this type of electrical and structural variability is in providing the conditions for any form of life. And on Titan in particular, these conditions seem ripe, even considering Titan’s frigid temperatures. “Polyimine could be photochemically active and drive chemistry on the surface [of Titan],” say the study’s authors, who believe that their conclusions about hydrogen cyanide’s properties on Titan should inform future space missions.
NASA’s decade-long Cassini mission to Saturn has produced astounding images and remarkable information about both the ringed planet and the moon, Titan, results made possible by the Cassini’s landing of its Huygens spacecraft on Titan in January 2005 as the first successful landing of a spacecraft from Earth on a body in the outer solar system.
Recently, scientists have used the data sent home by Cassini to solve a riddle about how Titan’s surface got its depressions which formed its liquid methane and ethane lakes. In a process much the same as that which creates sinkholes, caves and salt-pans here on Earth, the surface of Titan has been shown to be in part composed of rocks and organic material that has eroded over time, producing the lake-filled indentations on Titan.