On the atmospheric origin of weak absorption features in the infrared spectrum of Mars

Abstract

Two weak absorption features identified in the near‐infrared of Mars, at 2.35 μm and 3.8 μm, have been tentatively identified as mineralogic signatures. We suggest that these features are mostly due to the Martian atmosphere. The 3.8‐μm feature, as well as other weaker features around 3.6 and 4 μm, is probably due to weak isotopic bands of carbon dioxide and is well fitted with a nominal atmospheric model assuming a CO2 pressure of 7 mbar at the zero‐altitude level. The 2.35‐μm feature observed in the region of Arabia is primarily due to the 2–0 band of CO in the Martian atmosphere and, at first order, is well fitted with the same nominal atmospheric model, assuming the canonical value CO/CO2 = 0.0007. There might be a weak remaining absorption of mineralogic origin, especially at 2.285 μm and 2.41 μm.