Latitudinal and local time distribution of the O2 infrared nightglow and O density in the lower thermosphere

Atomic oxygen is the major component in the Earth’s upper thermosphere. The O density reaches a maximum of about 3x1010 cm-3 near 100 km. The 1.27 µm emission of the IR Atmospheric bands generated by recombination of O atoms has been observed in the nightglow. On the night side, the O2 airglow peaks at ~95 km with a value of ~10 MR.
<br />Atomic oxygen is present in the Martian atmos-phere but that the intensities values are below the cur-rent instrument detectability threshold. The Mars at-mosphere oxygen density is highly variable, depending on the altitude, temperature, latitude and longitude.
<br />On Venus, atomic oxygen has been measured in situ only above 145 km on both the day and the night sides. Limb observations obtained with the Venus In-frared Thermal Imaging Spectrometer (VIRTIS) on board Venus Express show that the O2 infrared nightglow peaks at ~97 km, with a mean intensity val-ue of about 1,3 MR [1, 2]. Yet, the distribution is largely inhomogeneous, with an enhanced region of ~3 MR statistically located near the midnight meridian at low latitude [3]. The oxygen density can be mapped using the O2 airglow and CO2 density vertical distribu-tions [4]. The O2 volume emission rates are obtained with an Abel inversion of the O2 limb profiles and CO2 vertical distributions are taken from the Venus International Reference Atmosphere (VIRA) model. The results show that the O density peak is located between 93 and 105 km (with a mean value of 104 km) and ranges from 2.8x1010 to 8.5x1011 cm-3 (with a mean value of 2.2x1011 cm-3). No correlations between the peak altitude and the latitude or the peak altitude and the local time are observed. However, the O density decreases and its variability increases while moving away from the antisolar point.