The potential for chemical evolution on Titan

Saturn´s moon, Titan, is a Mercury-sized body that is rich in organics and water ice. The Cassini-Huygens mission will arrive at Saturn in July 2004 and deploy the European Space Agency (ESA) Huygens probe, which will descend to the surface, providing in situ chemical analysis, images, spectra and other data that will characterize in detail the atmosphere and, if it survives, a region of the surface. The Saturn Orbiter instruments will map Titan´s surface at a range of wavelengths over 4 years and approximately 45 flybys. Radar and near-IR mapping will distinguish between areas of water ice, ammonia-water, and organics, as well as provide perhaps sufficient data to distinguish liquid organics from solid organics. We then need to be prepared to examine what scientific questions would follow from these results and what subsequent mission will enable a more complete picture of Titan to be developed. We propose that Titan is an exciting astrobiological target. If the Cassini/Huygen´s data show that there is no variation in the composition of surface organics, then atmospheric photochemistry has dominated the production of organics with little further evolution. However, if there is variation from region to region, this might suggest that additional organic chemistry has acted on the products of stratospheric photochemistry. Should evidence for variability in the organic phases on Titan be found, subsequent exploration of the surface ought to be undertaken, with an eye toward understanding the extent to which organic chemistry has proceeded. Sampling of organics to determine oxygen content, extent of acetylene polymerization, existence of chiral molecules and enantiomeric excesses, and searches for specific polymer products, would be of interest in assessing how organic chemistry evolves toward biochemistry. Such efforts would require fairly sophisticated chemical analyses from landed missions. This paper examines this chemistry and the potential instruments that could distinguish chemical evolution.