Life in the Solar System - Titan

One step further in the solar system lays Saturn, and its largest moon Titan seems to be one of the most serious candidates for life, however not a carbon based life. While recent images of this moon have revealed a celestial body that looks very much like Earth, the chemical composition of these features is quite different. Titan seems to be more like an early Earth. It has a thick atmosphere, with oceans and mountains, winds, river channels, dunes, as well as weather cycles and volcanism. The atmosphere on Titan is thick, hazy, and similar to Earth’s early atmosphere, composed of 90 percent nitrogen, as well as argon, methane and ethane. No oxygen means there is no water vapor, ozone or carbon dioxide. However there are greenhouse gases: methane and ethane. The methane condenses, forming clouds and methane rain. The lakes on this moon are made of liquid methane. Sunlight converts methane into ethane, generating organic compound. But it is cold on Titan: -180°C, and the atmospheric pressure on the surface is 50 percent greater than on Earth. [1] Titan is the only moon other than Earth’s to have been explored. In January 2005, the unmanned Huygens probe launched by the Cassini mission descended onto Titan’s surface. Recent studies from the Huygens probe suggest that there is hydrogen and acetylene on the surface of Titan, which could serve as nutrients for methanogens even in cold environments, and therefore the presence of primitive life on the surface of Titan is possible. [2] The chemistry of Titan looks hostile to carbon based life, but back on Earth psychrophiles thrive in extreme cold environments and use methane to produce energy. Either way, the resemblance to an early Earth and the complicated chemical processes on Titan are an excellent source of understanding prebiotic processes. [3]

Notes

[1] Seeds, Michael. The Solar System. Boston: Brooks/Cole, Cengage Learning, 2011, 593.

2 Atreya, Sushil K. "The Mystery of Methane on Mars & Titan. (Cover story)." Scientific American 296, no. 5 (May 2007): 42-51. Academic Search Premier, EBSCOhost (accessed October 11, 2011), 51.

3 Raulin, Francois. "Astrobiology and Habitability of Titan." Space Science Reviews 135, no. 1-4 (March 2008): 37-48. Academic Search Premier, EBSCOhost (accessed October 11, 2011), 46.