Session 2: Solar, Planetary and Space Physics

Title:  The atmosphere and surface of Titan investigated from the ground and from space
Author(s):   A. Coustenis (Poster)

Titan, Saturnís largest satellite is currently the only confirmed exobiotical environment known to us. It is also perhaps the most intriguing object in our Solar System. Its uncanny resemblance to our own planet has motivated generations of scientists into studying it from both the space and from the ground, and has initiated the Saturn-bound Cassini/Huygens ESA/NASA mission (arrival at Titan is scheduled for end of 2004).
  In the meantime, Titan is observed from the ground (using large telescopes, such as those in Hawaii and Chile), but also from space (initially with Voyager 1 and 2, with the HST, and recently with ISO).
  Thus, we know today that the thick atmosphere layer covering the yet-to-be-determined satelliteís surface, is essentially made of nitrogen, with small amounts of methane and hydrogen. The combination among these mother molecules yields an exciting organic chemistry in Titanís atmosphere, with hydrocarbons and nitriles (one of the latter, HCN, is a prebiotic molecule). As a difference with our own planet one should mention the absence of significant amounts of oxygen (only traces of CO, CO2 and more recently, H2O have been discovered), as well as the low temperatures prevailing (180 K in the atmosphere and 94 K on the surface) that delay chemical reactions.
  Titanís surface is hidden under a veil of a thick aerosol cloud, but recently, spectroscopy and imaging of the satellite in the near-IR have shown that this surface is inhomogeneous, bright on the leading side and darker on the trailing one. A large, bright, equatorial region - possibly connected with relief - is found on the leading hemisphere, while bright areas are also observed near the poles. The exact nature of this ground remains to be discovered, but is probably a mixture of ices (H2O, CH4, CO2...), hydrocarbon liquid and rocks. 
  We will discuss the implications of recent observations on the nature and the origins of Titan and its connection with our own planet.