Observations of the (1-0) band of CO in Venus using VIRTIS-H aboard Venus Express

We have used infrared spectra of the dark side of Venus, recorded by the VIRTIS-H spectrometer (Drossart et al. Proc. SPIE 5543, 175, 2014) aboard Venus Express (Svedhem et al. JGR 113, E00B33, 2008), to analyze the CO (1-0) band around 4.7 µm. The resolving power of VIRTIS-H (about 1200) is sufficient to separate the individual lines of CO. We have selected two sets of spectra, the first one at mid-latitude (43°S) and the other in the polar collar (69-83°S). The CO individual lines appear in absorption in the first case, and in emission in the second case, as a consequence of a temperature inversion occurring at high latitude at the level of the upper cloud top. Synthetic models have been calculated using the Planetary Spectrum Generator (Villanueva et al. JQSRT 217, 86, 2018). Information is retrieved on the thermal vertical profile and the CO vertical distribution at both latitudes. This work illustrates the capabilities of high-resolution infrared spectroscopy for monitoring minor atmospheric species in the mesosphere of Venus, in the perspective of the EnVision mission (Helbert et al. Proc. SPIE 11128, A1112804, 2019).