Simultaneous mapping of CO, SO2 and HDO on the night side of Venus

In order to better understand the photochemical and dynamical processes which drive the atmosphere of Venus, we have started in January 2012 an observing campaign to monitor the behavior of sulfur dioxide and water near the cloud top of Venus, using the TEXES (Texas Echelon Cross-Echelle Spectrograph) imaging spectrometer at the NASA InfraRed Telescope Facility (IRTF, Mauna Kea Observatory ; Encrenaz et al. Astron. Astrophys. 703, id.A219, 2025). These data have shown evidence for drastic changes in the SO2 abundance, both on the short term and the long term, the origin of which is unclear, as well as a strong spatial variability at low latitudes. In February 2025, data have  been obtained at 4.7 and 7.4 microns on the night side of Venus (49 arcsec in diameter), allowing us for the first time to map simultaneously  CO, SO2 and H2O (through its proxy HDO) near the cloud top of Venus. The data seem to show a slight enhancement of CO around midnight, consistent with the results previously reported from millimeter/submillimeter observations in the upper mesosphere (Clancy et al. Icarus 217, 779, 2012). The TEXES data will be used in an attempt to constrain coupled dynamical-chemical GCM simulations of the Venus atmosphere (e.g. Shao et al., AGU General Conference, New Orleans, USA, December 2025).