There have been countless media reports recently claiming, with various levels of veracity, that NASA had detected evidence of life on Titan, the largest moon of Saturn. The fact is, simply, that this claim is misleading at best.
Could Life Exist on Titan?
Now, of all the bodies in our solar system, Titan appears as fit as any to support life. It has a relatively dense atmosphere (something that other objects, like mars, are lacking) and sufficient size and structure to maintain the properties necessary for life to evolve. Naturally, then, scientists have begun to look for evidence of life on the surface.
There are differences between Titan and the Earth that would necessitate that life would evolve quite differently. Specifically, Titan is much too cold to contain liquid water on its surface, and the atmospheric composition is considerably different than our own. As a result, it is believed that Hydrogen, an abundant element in Titan's atmosphere, would be the primary element "breathed" by life on the surface (rather than the mix of nitrogen and oxygen mixture we breathe). Of course this statement is pure conjecture as well, though it does make sense and is probably the least controversial element of the debate.
How Would We Know If Life Existed on Titan?
So assuming that any life form evolving on the surface of Titan would breathe hydrogen, scientists began studying how hydrogen moves through the atmosphere and on the surface. What they found is that the hydrogen flows in the atmosphere seem to disappear at the surface. Moreover, geological studies of the surface seem to indicate a lack of the element in the surface structure.
The conclusion drawn is that the hydrogen must be absorbed by life on the surface. The problem is that this is not the only possible explanation. Other chemical processes could cause hydrogen to bind with other elements to form more complex molecules, especially when you start considering the addition of energy from the Sun in these reactions. (In the interest of full disclosure I should note that one such reaction would be the formation of acetylene gas in the atmosphere, but the Cassini probe was not able to detect significant amounts of this gas. But more measurements are warranted before drawing a definitive conclusion.)
Where Do We Go From Here?
What is perhaps the most puzzling part of the story is that it is very cold on Titan's surface. This is important because all that we know about the formation of life suggests that energy, likely in the form of heat, is a vital part of the process. It truly would be amazing for life to have formed in such conditions as it would seemingly go against conventional wisdom.
However, given the building blocks that are in place on the icy moon, it is more likely that life will involve in the future. Several billion years from now the Sun is going to enter the next step in its evolutionary cycle and become a red giant, expanding significantly and swallowing up the first four planets in our solar system. (Including us!) At this point the temperature on Titan will rise significantly, possibly giving rise to the evolution of life. (Of course, assuming that it does not already exist.)
Ultimately what we have are a series of interesting results that, under certain assumptions, could indicate the possibility of life on another world. However, it seems that we may be getting ahead of ourselves. We still do not have all the facts and there are other possibilities that must be explored.
Titan has the fundamental building blocks necessary for life, but it is just not clear, despite reports to the contrary, that life has arrived. It will be interesting to see what the future holds as we continue to study this dynamic world.
