Title: The atmosphere and surface of Titan
investigated from the ground and from space
Author(s): A. Coustenis (Poster)
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.
will discuss the implications of recent observations on the nature and
the origins of Titan and its connection with our own planet.