Hydrogen peroxide on Mars:: Evidence for spatial and seasonal variations

Hydrogen peroxide (H2O2) has been suggested as a possible oxidizer of the martian surface. Photochemical models predict a mean column density in the range of 10(15)-10(16) cm(-2). However, a stringent upper limit of the H2O2 abundance on Mars (9 x 10(14) cm(-2)) was derived in February 2001 from ground-based infra red spectroscopy, at a time corresponding to a maximum water vapor abundance in the northern summer (30 pr. mum, Ls = 112degrees). Here we report the detection of H2O2 on Mars in June 2003, and its mapping over the martian disk using the same technique, during the southern spring (Ls = 206degrees) when the global water vapor abundance was similar to10 pr. Pm. The spatial distribution of H2O2 shows a maximum in the morning around the sub-solar latitude. The mean H2O2 column density (6 x 10(15) cm(-2)) is significantly greater than our previous upper limit, pointing to seasonal variations. Our new result is globally consistent with the predictions of photochemical models, and also with submillimeter ground-based measurements obtained in September 2003 (Ls = 254degrees), averaged over the martian disk (Clancy et al., 2004, Icarus 168, 116-12 1). (C) 2004 Elsevier Inc. All rights reserved.