Ground-based IR imaging spectroscopy of Mars

Rapid improvements in the performance of near-IR (1-5 mum) instrumentation on large telescopes are making possible spectroscopic studies of Mars from ground-based observatories with a combination of spectral and spatial resolution, which has hitherto been impossible. We describe here the preliminary results of observations obtained during the very favourable opposition of August 2003 using the UIST instrument on the United Kingdom Infrared Telescope (UKIRT) on Mauna Kea, Hawaii. Infrared spectral scans of the disk were obtained at a range of near-IR wavelengths and resolving powers. The observations cover wavelengths, which include absorption features due to a range of potential surface minerals, H2O and CO2 ice, and atmospheric gases including CO2 and a number of trace gases. Such observations can be used to search for evidence of the past presence of surface water, and to measure atmospheric properties. The new generation of extremely large telescopes (30-100m aperture) and advanced adaptive optics system, now under development, have the potential to improve the spatial resolution of ground-based observations by more than an order of magnitude, to a few km at the surface of Mars. We discuss some of the problems in using adaptive optics to observe Mars and how they may be overcome.