The following document lists the file abstract/RCOURTIN_TITAN5_7.abs
from catalogue VI/111.
A plain copy of the file
(without headers/trailers) may be downloaded.
We propose to make medium-resolution (R = 1000) spectroscopic observations of Titan in the 5-to-7 mum range. This part of the spectrum contains important information in three fundamental areas of Titan's physico-chemistry: the organic haze, the surface, and the high-altitude photochemistry. Theoretical modeling of Titan's radiation show that this wavelength interval corresponds to the transition between reflected sunlight and thermal emission. The two components should be of equal intensity near 6.0 mum, and the spectral shape of that transition should be mostly diagnostic of the haze optical properties. The proposed measurements would provide a definite test of the tentative identification of the haze material with laboratory-synthesized organics or "tholins". At shorter wavelengths, current models as well as spectrally-resolved observations at 1-5 mum, suggest that the haze becomes more transparent, allowing to sense the surface or near-surface layers. Albedo measurements between 5 and 6 mum would provide crucial information on the composition and physical properties of the surface, and hence, on the origin and evolution of Titan. At wavelengths longer than 6 mum, the thermal emission regime allows to probe warm stratospheric layers where photochemically-produced as well as exogenic molecular species in the vapor phase produce strong emission lines. The detection of such molecular transitions, in particular those of H2O near 6.3 mum, would further our understanding of Titan's unique chemistry. The ISO satellite offers the sole opportunity to explore that part of the spectrum, since telluric water vapor absorption makes such observations impossible or at best very uncertain from ground-based or airborne observatories. Moreover, the Cassini/Huygens instrument payload will not permit remote observations in that range.