In my previous post, I made a mention of Saturn’s moon Titan being a possible host for extraterrestrial life. Turns out that Titan was discovered on this very day, March 25, back in 1655 by the Dutch astronomer Christiaan Huygens. Given this fact, I thought it would be fun to take a closer look at this moon. What’s so special about it? Why do astronomers think it could harbor life?
A major point of interest is that Titan is the only moon discovered so far that has a substantial atmosphere. It’s atmosphere is about 1.5 times as thick as Earth’s and, like Earth’s, is dominated by nitrogen (McKay, 2005). Along with nitrogen, the atmosphere is rich in organic compounds such as methane and other hydrocarbons (Lemonick, 2010). Obviously, these conditions are very different from what we see here on Earth, but astrobiologists think that the atmosphere provides precursors for, and can sustain, life. Experiments conducted at the University of Arizona have demonstrated that DNA/RNA bases cytosine, adenine, thymine, guanine, and uracil and amino acids glycine and alanine can be produced from the ingredients in Titan’s atmospheric haze (2010).
Interestingly, Titan’s surface is devoid of liquid water, which seems to argue against its ability to support life. Yet, others argue that life can exist in the liquid methane lakes that dot Titan’s surface, shown in the image above. These lifeforms would use acetylene, ethane, and other organic solids in combination with hydrogen to derive energy for sustenance (McKay & Smith, 2005). Supporting this idea is the fact that certain lifeforms on Earth, microorganisms called methanogens, exist in a similar manner. The science behind this theory is very dense, so I won’t write it all out here. Instead, I refer you to the 2005 paper written by McKay and Smith which discusses the matter. Furthermore, while the surface does not have water, scientists believe that Titan does have a global subsurface ocean, composed of a water-ammonia mix. As Fortes (2002) writes, conditions within this hypothetical ocean, while extreme by terrestrial standards, are such that life could indeed survive.
In 2005, the Huygens probe landed on Titan’s surface, marking the first landing done in the outer solar system. Atmospheric and surface data obtained by Huygens possibly indicated the presence of methanogen-like life (McKay, 2010). However, abiotic chemical or geological processes cannot be completely discounted. Ultimately, it will take many years of study and exploration to uncover Titan’s secrets. But, if what’s been discovered so far is any indication, the undertaking promises to yield intriguing results. I, for one, am hoping that life is one of them.
To read more:
The article by McKay and Smith: http://www.sciencedirect.com/science/article/pii/S0019103505002009
The article by Fortes: http://www.sciencedirect.com/science/article/pii/S0019103500964005