Mathematics
Scientific paper
Jun 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001p%26ss...49..731e&link_type=abstract
Planetary and Space Science, Volume 49, Issue 7, p. 731-741.
Mathematics
17
Scientific paper
Millimeter observations of Mars were performed in April /1997, near opposition, using heterodyne spectroscopy with the IRAM 30-m antenna at Pico Veleta (Spain). During the observations, the northern latitude of the sub-Earth point was about /24°. The planetocentric longitude of the Sun (Ls) was close to /100°, which corresponds to the beginning of Martian northern summer, when the water vapor abundance is expected to be maximum at high northern latitudes. A strong emission was detected in the 226GHz transition of HDO at the disk center /(latitude=+24°) and around the north pole. The 203GHz transition of H218O was also unambiguously detected. The thermal profile was retrieved from the simultaneous observation of 12CO(2-1) at 230GHz, 13CO(2-1) at 220GHz and 12CO(1-0) at 115GHz. Using both HDO and H218O transitions, we derive a water vapor content of 52(+34,-23)prμm at the disk center and 85(+30,-33)prμm at the north pole. These high values are consistent with the seasonal water cycle found by the MAWD Viking data (Jakosky, Haberle, in: H.H. Kieffer, B.M. Jakosly, C.N. Synder, M.S. Mathews (Eds.), Mars, University of Arizona Press, /1992.) in the case of the northern region, but higher than the Viking estimates at low latitude. The water vapor profile was found to be saturated at a level of 9(+5/-4)km at the disk center and 5(+3,-2)km at the north pole. These saturation levels are consistent with MAWD Viking data (H.M. Hart, Seasonal changes in the abundance and vertical distribution of water vapor in the atmosphere of Mars, Ph.D. Thesis, University of Colorado, 1989) and with millimeter measurements performed by Clancy et al. (Icarus 122 (1996) 36); they confirm that water is confined to the lower troposphere near aphelion. The quality of our data did not allow us to derive a precise determination of the /D/H Martian ratio, which is found to be, within a factor of 2, equal to 6 times the terrestrial ratio, in agreement with previous measurements.
Encrenaz Th.
Gulkis Sam
Lellouch Emmanuel
Paubert Gabriel
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