High-resolution infrared spectrum of CO on Mars: Evidence for emission lines

Very-high resolution observations of Mars at 5 μm allowed detection of emission lines belonging to the 1-0 and 2-1 vibrational bands of CO. These transitions can be produced either by fluorescence following solar infrared excitation or by photolysis of CO2 yielding CO in excited states. A quantitative model taking into account these two NLTE mechanisms successfully reproduces the observed intensities. The rotational distribution of the 2-1 band is consistent with a rotational temperature of 130 ± 30 K at an altitude of 55 km.