A layer of ozone detected in the nightside upper atmosphere of Venus

Abstract

International audienceTo date, ozone has only been identified in the atmospheres of Earth and Mars. This study reports the first detection of ozone in the atmosphere of Venus by the SPICAV ultraviolet instrument onboard the Venus Express spacecraft. Venusian ozone is characterized by a vertically confined and horizontally variable layer residing in the thermosphere at a mean altitude of 100 km, with local concentrations of the order of 107-108 molecules.cm-3. The observed ozone concentrations are consistent with values expected for a chlorine-catalyzed destruction scheme, indicating that the key chemical reactions operating in Earth's upper stratosphere may also operate on Venus

The OH Venus nightglow spectrum: Intensity and vibrational composition from VIRTIS—Venus Express observations

“…This one-dimensional photochemical model involves 61 reactions and 24 species and was specifically adapted to the Venus nightside. As discussed by Montmessin et al (2011), the observed ozone peak density is significantly less than the modelled 3.9x10 9 cm -3 , probably because the chlorine mixing ratio was underestimated in the photochemical model. Also, one-dimensional models do not consider the global circulation of the atmosphere, which is however very important to correctly reproduce density distributions (Brecht et al, 2011(Brecht et al, , 2012.…”

“…The CO 2 density profile was derived from stellar occultations with the SPICAV instrument. Similarly, the ozone peak density is based on the recent SPICAV detections of an ozone layer near 110 km by Montmessin et al (2011). The O vertical distribution is obtained from the analysis of the O 2 (a 1 ∆) emission at 1.27 μm observed with the VIRTIS instrument.…”

“…Using 29 stellar occultation detections of ozone, Montmessin et al (2011) deduced that the O 3 layer is on the average located at 99±10 km with a peak value ranging from 10 7 to 10 8 molecules cm -3 . However, densities at only 1 to 3 altitudes around the peak are measured by SPICAV with sufficient signal to noise ratio.…”

“…Characteristics of the Atmosphere of Venus (SPICAV) instrument on board Venus Express by Montmessin et al (2011) provides support for the Bates-Nicolet mechanism as the main chemical reaction to produce excited OH in the Venus atmosphere. Nevertheless, this mechanism initially mainly populates the v=6-9 vibrational levels.…”

“…Even more recently, Montmessin et al (2011) discovered the presence of O 3 in the nightside upper atmosphere.…”