[Previous] | [Session 15] | [Next]
Th. Encrenaz (Obs. Paris), T. Greathouse (U. Texas), B. Bezard (Obs. Paris), S.K. Atreya, A.S. Wong (U. Michigan), M. Richter, J. Lacy (U. Texas)
We have searched for H2O2 in the northern atmosphere of Mars, on Feb 2-3, 2001 (Ls = 112 deg.), at a time corresponding to maximum water vapor abundance in the northern hemisphere. The TEXES high-resolution grating spectrograph was used at the NASA/Infrared Telescope Facility (IRTF). Individual lines of the H2O2 \nu6 band have been searched for in the 1226-1235 cm-1 range (8.10-8.15 \mum). Data have been co-added for three different latitude sets: (1) full northern coverage (0-90 deg.); (2) low northern latitudes (10-40 deg.); (3) high northern latitudes (40-60 deg.). From the absence of detectable H2O2 lines in each of the three co-added data sets, we infer an H2O2 2-\sigma upper limit of 7 1014 cm-2 in the first case, 2 1015 cm-2 in the second case, and 1015 cm-2 in the third case. These numbers correspond respectively to mean water vapor abundances of 30 pr-\mum, 20 pr-\mum and 40 pr-\mum at the time of our observations. Our lowest upper limit is ten times lower than the value derived by Krasnopolsky et al. (1997) in the southern hemisphere in June 1988 (Ls = 222 deg.); the mean water vapor abundance corresponding to their observation was 10 pr-\mum. Our lowest upper limit is about 10 times lower than the values predicted by global photochemical models, also calculated for a mean H2O abundance of 10 pr-\mum. However, taking into account the actual geometry of the observations and the corresponding conditions in the Martian atmosphere, the calculated H2O2 abundance becomes close to the observed upper limits by assuming an eddy diffusion coefficient of 107 cm2s-1 in the lower atmosphere of Mars.
If the author provided an email address or URL for general inquiries,
it is as follows:
Bulletin of the American Astronomical Society, 34, #3< br> © 2002. The American Astronomical Soceity.