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

Nicolas Biver (1, 2, 3, 4) , Alain Lecacheux (1, 2, 3, 4) , Thérèse Encrenaz (1, 2, 3, 4) , Emmanuel Lellouch (1, 2, 3, 4) , Philippe Baron (1, 2, 3, 4, 5) , Jacques Crovisier (1, 2, 3, 4) , Urban Frisk (6) , Åke Hjalmarson (7) , Michael Olberg (7) , Aage Sandqvist (8) , Sun Kwok (9)

1 LESIA - Laboratoire d'études spatiales et d'instrumentation en astrophysique
2 Ingénieurs, Techniciens et Administratifs
3 Physique des plasmas
4 Pôle Planétologie du LESIA
5 NOVELTIS [Sté]
6 SSC - Swedish Space Corporation
7 OSO - Onsala Space Observatory, Chalmers University of Technology
8 Stockholm Observatory, AlbaNova University Center
9 University of Calgary

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 sigma 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 H2¹⁸O 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 mum.

Domaines: Astrophysique [astro-ph]

Nicolas Biver, Alain Lecacheux, Thérèse Encrenaz, Emmanuel Lellouch, Philippe Baron, et al.. Wide-band observations of the 557 GHz water line in Mars with Odin. Astronomy and Astrophysics - A&A, 2005, 435, pp.765-772. ⟨10.1051/0004-6361:20042247⟩. ⟨hal-03724074⟩