Observation of O 2 1.27 μm dayglow by SPICAM IR: Seasonal distribution for the first Martian year of Mars Express

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The O 2 (a 1 Δ g ) molecule is a result of the photodissociation of ozone in the Martian atmosphere and may be used as a tracer for atmospheric ozone mostly above ∼20 km since the singlet delta state is quenched by carbon dioxide at lower altitudes. The SPICAM IR acousto‐optic tunable filter (AOTF) spectrometer is a part of the SPICAM experiment onboard Mars Express. It is able to measure the O 2 singlet delta emission band at 1.27 μm with a resolving power of ∼2200. We present the first seasonal map of the O 2 emission covering the entire Martian year. Maximal values of O 2 emission are observed during late winter to early spring at high latitudes in both hemispheres. We report the highest dayglow intensity of 30 MR in the southern hemisphere (70°–80°S latitudes) at L s = 185°–195° and of 26 MR in the north polar regions (latitudes 70°–80°N) at L s = 10°–20°. The lowest emissions are measured during the southern hemisphere summer near perihelion (L s = 270°–330°), with an upper limit of 1–2 MR. At low latitudes (30°S–30°N) the seasonal evolution of the O 2 emission shows a distinct maximum (5–7 MR) near aphelion. This is consistent with the maximum in O 3 occurring at this time of the year, which has been reported from Earth, from satellite, or by modeling studies. The comparison of our results with previous measurements carried out from Earth shows quantitative differences that can be attributed to differences in local time of the observation or interannual variability of the Martian ozone layer.