An Overview Of Spicav/soir Results On The Atmosphere Of Venus From Venus Express Mission

SPICAV/SOIR is a suite of three spectrometers in the UV and IR range flying on ESA Venus Express orbiter, dedicated to the study of the atmosphere of Venus : UV (110-320 nm), Vis-Nir (0.65-1.65 µm), and mid IR (2.3-4.4 µm). The UV spectrometer discovered a high altitude layer of SO2 ( 85-105 km), apparently correlated with the density of haze particles. Ozone is detected for the first time in the atmosphere of Venus. The night side γ and δ bands of NO intensities are maximal at 2 am (influence of super-rotation), while the O2 emission mapped simultaneously by Virtis peaking at 95 km altitude ( 10 km below NO emission) is centered at midnight, a puzzle for general circulation models. The hot hydrogen component of the exosphere, extending at more than 30,000 km, is variable. The SPICAV VIS-IR sensor (0.7-1.7 μm, resolution 0.5-1.2 nm) employs a pioneering technology: acousto-optical tunable filter (AOTF). Day side observations indicate a variable latitude distribution of cloud top altitude (decreasing toward the pole) and water vapor mixing ratio. The SOIR spectrometer is a new Solar Occultation IR spectrometer in the range λ=2.2-4.3 µm, with a spectral resolution λ/Πλ>20,000, the highest ever flown in a planetary mission. This new concept includes a combination of an echelle grating and an AOTF crystal to sort out one order at a time. Vertical profiles of CO, HDO, H2O, HCl, SO[SUB]2[/SUB], CO[SUB]2[/SUB] isotopes and temperature are regularly retrieved, as well as aerosols. The CO mixing ratio (80-130 km), a tracer of atmospheric exchange from thermosphere to lower atmosphere, is 10 times less than the VIRA model prescription, showing also some time variability.