Formation of Complex Molecules
While the Cassini–Huygens mission was not equipped to provide evidence for biosignatures or complex organics, it showed an environment on Titan that is similar, in some ways, to ones theorized for the primordial Earth. Scientists think that the atmosphere of early Earth was similar in composition to the current atmosphere on Titan, with the important exception of a lack of water vapor on Titan. Many hypotheses have developed that attempt to bridge the step from chemical to biological evolution.
The Miller-Urey experiment and several following experiments have shown that with an atmosphere similar to that of Titan and the addition of UV radiation, complex molecules and polymer substances like tholins can be generated. The reaction starts with dissociation of nitrogen and methane, forming hydrogen cyanide and acetylene. Further reactions have been studied extensively.
In October 2010, Sarah Horst of the University of Arizona reported finding the five nucleotide bases -- building blocks of DNA and RNA -- among the many compounds produced when energy was applied to a combination of gases like those in Titan's atmosphere. Horst also found amino acids, the building blocks of protein. She said it was the first time nucleotide bases and amino acids had been found in such an experiment without liquid water being present.
Read more about this topic: Life On Titan
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