Limits to the abundance of surface CO2 ice on Titan

摘要

In the context of the Cassini/Huygens mission, we performed supporting ground-based observations to complement the results from the NASA/ESA/ASI space mission to the Saturnian system with particular focus on Titan. On the nights of 18 and 19 December 2004, we conducted adaptive optics observations with VLT/NACO to search for and map the distribution of CO2 ice deposits on the spatially resolved surface of Titan (65 mas resolution). This experiment became possible because (1) solid CO2 possesses two narrow and strong absorption lines at 2012 nm and 2070 nm that fall into the 2.05 μm window of Titan's atmosphere and (2) the width of these bands matches the band pass of the Fabry-Perot instrument installed in NACO. We do not detect this chemical compound, but we can derive firm limits on the abundance of CO2 ice on the surface of Titan at sub-Earth longitudes 284°W and 307°W. With a spatial sampling of 65 mas, we conclude that a partial surface coverage of segregated CO2 ice does not exceed 7% or 14% for bright or dark surface regions, respectively.