NASA Astrobiology Institute (NAI)

Titan First

Robert Shapiro (New York University) and Dirk Schulze-Makuch (Washington State University)

The Titan Saturn System Mission is planned to consist of a NASA orbiter, an ESA lander and a research balloon. Artist's image shows lander on one of Titan's hydrocarbon lakes with Saturn in the background.

We have written a paper “The Search for Alien Life in Our Solar System: Strategies and Priorities” which is now on line http://www.liebertonline.com/toc/ast/0/0 and will soon appear in Issue #4 (2009) of Astrobiology. We argue that Titan should be given the highest priority in the search for existing alien life in our Solar System, followed by Mars and Europa in that order. In setting priorities, we assume that economic constraints may limit existing space agencies to only one new multi-billion dollar planetary exploration mission, comparable to Galileo and Cassini, in the coming decades. We would be happy if our pessimism was unjustified, but still feel that prioritization is worthwhile as a precaution.

In considering our search for understanding of the origin of life, rather than the discovery of alien life, we hold that Titan is again an easy winner. Familiar life on Earth centers on the chemistry of carbon, and we are ignorant about the steps through which an unorganized chemical mixture of the type produced by abiotic organic chemistry can be converted by an energy flow into a metabolizing, reproducing system. We would benefit greatly by learning more about the detailed organic chemistry of our Solar System.

At present, our knowledge of unorganized abiotic mixtures comes almost entirely from meteorites. The study of such mixtures on planetary surfaces would enrich our knowledge of the starting materials from which carbon-based life may be constructed. If we were lucky, we might even encounter a mixture in which some degree of self-organization has taken place. This could occur through novel processes at low temperature, or during episodes in which the surface of Titan has been heated temporarily by a volcanic eruption or meteoric impact.

Titan is rich in organics, and the materials are available at the surface. The plumes and near-surface regions of Enceladus also offer organics, and their exploration could be bundled into a return mission to Titan. Only trace amounts of methane have been confirmed thus far on Mars, and they appear to originate from the deeper interior and thus may be difficult to access. The internal Europan ocean may support life, but it is rather inaccessible, and no carbon compounds have as yet been detected on the surface. Further exploration of Titan therefore deserves the strongest backing from the origin-of-life community.