Wide-band observations of the 557 GHz water line in Mars with Odin

Abstract

The Odin satellite, thanks to the versatility of its receiver and spectrometer system, is well suited for the study of wide planetary submillimetre lines. In June and November 2003, the H2O line at 557 GHz was observed in the Mars atmosphere over a total bandwidth of 4 GHz. The wings of the line are detected up to the nearby continuum, which provides constraints on the disc-averaged vertical thermal profile and atmospheric water mixing ratio. In parallel, a sensitive search for the O2 line at 487 GHz was undertaken in June. This search was negative with a 3 σ upper limit of 4% on the absorption line depth, which is twice the expected signal. This observation, however, provides information on the continuum of Mars. In November the CO J(5-4) and the H2 18O lines were also detected in parallel and provide additional constraints on the temperature profile and mixing ratios. Surface water mixing ratios of 2-3 × 10 -4 are inferred, corresponding to column densities in the range of 10-15 precipitable μm. © ESO 2005.