CRISM Limb Observations of O2 Singlet Delta Nightglow in the Polar Winter Atmosphere of Mars

International audienceCRISM (Compact Reconnaissance Imaging Spectrometer for Mars) near-IR spectroscopic imaging of the Mars atmospheric limb supports vertical profiling of aerosol (ice and dust) and gas [H2O, CO, CO2, O2(1Δg)] constituents versus season (Ls), latitude, and (to a limited degree) longitude. These CRISM limb observations are obtained approximately every two months (15° Ls), over a full range of sunlighted latitudes for two MRO (Mars Reconnaissance Orbiter) orbits centered on equatorial longitudes of 100W and 300W. Daylight limb spectra indicate strong 1.27 µm atmospheric emission from the excited singlet delta of molecular oxygen, associated with photolysis of Mars atmospheric ozone. Limb observations extending to un-illuminated, polar night latitudes present a new source of O2(1Δg) emission at higher altitudes (40-55 km), associated with three body recombination of atomic oxygen [O+O+CO2 -> O2(1Δg) +CO2]. This nightglow requires strong poleward supply of atomic oxygen, produced from photolysis of CO2 at sunlighted latitudes and transported at high altitudes (above 70 km) into polar night altitudes of 40-60 km. CRISM limb observations indicate distinctive latitudinal and longitudinal distributions of this polar nightglow that evolve over the Feb-Aug 2010 (Ls=50-140°) period of observations for the southern winter. New observations include planned full orbit mapping (12 orbits) in August 2010 to characterize these spatial variations in more detail. Key comparisons with co-located MCS (Mars Climate Sounder) temperature and aerosol profile retrievals and LMD (Laboratoire Météoroligie Dynamique) GCM photochemical simulations provide new insights into poorly constrained meridional transport into polar winter latitudes on Mars