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

¹ LESIA, CNRS UMR 8109, Observatoire de Paris, 5 pl. J. Janssen, 92190 Meudon, France e-mail: nicolas.biver@obspm.fr
² Noveltis, Parc technologique du canal, 2 Av. de l'Europe, 31520 Ramonville St. Agne, France
³ Swedish Space Corporation, PO Box 4207, 17104 Solna, Sweden
⁴ Onsala Space Observatory, 43992 Onsala, Sweden
⁵ Stockholm Observatory, SCFAB-AlbaNova, 10691 Stockholm, Sweden
⁶ Dept. of Physics and Astronomy, University of Calgary, Calgary, AB T2N 1N4, Canada
⁷ Inst. of Astron. & Astrophys., Academia Sinica, PO Box 23-141, Taipei 106, Taiwan

Received: 25 October 2004
Accepted: 17 January 2005

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 HO lines were also detected in parallel and provide additional constraints on the temperature profile and mixing ratios. Surface water mixing ratios of are inferred, corresponding to column densities in the range of 10-15 precipitable μm.