ESA - Venus Express Mission patch.
April 4, 2021
Graphic above: Map of observations of sulfur dioxide (A) and ozone (B) in the night hemisphere of Venus at heights of 85-100 km according to SPICAV-UV data for 2006-2014 of the Venus Express mission (ESA). Local time is shown horizontally; vertical - latitude. The asterisks indicate the cases of detection, the empty circles - the rest of the observations, where the absorption of gases was not registered. Graphic Credit: Evdokimova et al. (2021).
In the nighttime atmosphere of Venus at altitudes of 85–100 km, there is extremely little ozone, and the sulfur dioxide content changes significantly over several days. These conclusions were made based on the results of processing the data from the SPICAV instrument on board the Venus Express spacecraft, created with the active participation of the Space Research Institute of the Russian Academy of Sciences. An article with the results of the work was published in the Journal of Geophysical Research: Planets.
The Venus Express orbital spacecraft of the European Space Agency operated near Venus in 2006–2014. On board was installed, among other scientific instruments, a complex of spectrometers SPICAV / SOIR (Spectroscopy for the Investigation of the Characteristics of the Atmosphere of Venus), created with the active participation of the Space Research Institute of the Russian Academy of Sciences. The ultraviolet channel of the SPICAV spectrometer was the only instrument on board the Venus Express capable of simultaneously studying the distribution of elevated concentrations of such trace gases as ozone (O₃) and sulfur dioxide (SO₂) in the upper mesosphere of Venus.
Venus Express
This layer of the atmosphere corresponds to heights of 85–100 km, and is very interesting for researchers, since there is a zone of intersection of various modes of global atmospheric circulation. The behavior of ozone and sulfur dioxide in this region of the atmosphere on the night side, not illuminated by the Sun, has been rather poorly studied so far due to a lack of experimental data.
Now this has become possible thanks to the method of observations in the mode of stellar transmission, first implemented on Venus by the SPICAV spectrometer. The spectrometer "followed" the stars as they rise and set over the horizon of the planet and measured the spectra of their radiation, which passed through the atmosphere and was absorbed by its molecules. Thanks to this, it was possible to measure the concentrations of carbon dioxide (CO2 is the main component of the atmosphere of Venus), SO₂ and O₃ at altitudes of 85–100 km.
Ozone was first detected in the atmosphere of Venus also thanks to Venus Express in 2011. Then it was possible to establish that the Venusian ozone layer is located approximately at an altitude of 100 km with a concentration of approximately 107-108 molecules per cm3, but these were only the first observations. Daria Evdokimova and Denis Belyaev, researchers at the Planetary Physics Department of the IKI RAS and the first authors of an article published in JGR: Planets, presented for the first time the results of a combined analysis of the ozone and sulfur dioxide content for all eight years of SPICAV observations.
“We recorded only the maximum ozone concentrations in the atmosphere of Venus at altitudes of 85–100 km, that is, from 107 to 108 molecules per cubic centimeter,” explains Daria Evdokimova. - These values were obtained in 132 sessions of observations, and they show an extremely small content of this gas on the planet compared to the earth, which is about 10 thousand times more. The accumulated statistics, however, made it possible to estimate the average altitude profile of the relative content of O₃, that is, the ratio of the ozone density to the density of carbon dioxide as the main component of the atmosphere. In the studied altitude range, the estimated abundance increases from 1–30 parts per billion in volume (ppbv) at an altitude of 90 km to 6–120 ppbv per 100 km ”.
The observed distribution of ozone, the researchers believe, indicates that this gas interacts with chemical compounds carried by winds from the daytime side of the hemisphere to the nighttime. For example, it can be chlorine compounds, which are known to quickly react with ozone and destroy it. Observations of sulfur dioxide over all the years of the SPICAV experiment showed that its concentrations change significantly over a short time (several Earth days) from several units to several hundred ppbv. However, in this case, on average over the profile, its relative content at heights of 85–100 km is constant and amounts to 135 ± 21 ppbv.
The presence of rapid and significant variations does not allow an unambiguous conclusion about the temporal or spatial distribution of SO₂ in the night hemisphere without the use of improved chemical models that take into account the global circulation of the atmosphere.
Venus Express instruments
“These results show that the upper mesosphere of Venus is a very changeable environment that has yet to be described theoretically,” says Denis Belyaev. - The experimental data we have obtained on the distribution of O₃ and SO₂ will make it possible to refine the models of atmospheric circulation in the cross transit zone of about 100 km and bring us closer to understanding the nature of the atmosphere of Venus. It is strikingly different from the earthly one in physical characteristics, nevertheless, similar chemical processes take place in it, in which ozone and sulfur oxides are involved ”.
The Venus Express automatic interplanetary spacecraft was launched on November 9, 2005 from the Baikonur Cosmodrome using the Soyuz-FG launch vehicle with the Fregat upper stage. The device entered the first elongated orbit around Venus on April 11, 2006. In February 2015, the device entered the atmosphere of Venus and completed its mission, but the processing of its data continues to this day.
Specialists of the Space Research Institute of the Russian Academy of Sciences took part in the development, manufacture and testing of two scientific instruments of the orbiter: a universal spectrometer and a high spectral resolution spectrometer SPICAV / SOIR (supervisors: J.-L. Bertaux / Jean-Loup Bertaux, France, O. I. Korablev, Russia, D. Nevejans / Dennis Nevejans, Belgium) and the planetary Fourier spectrometer PFS (made in Italy with the participation of Russia, scientific supervisor V. Formisano / Vittorio Formisano, Italy, L.V. Zasova, Russia). In the experiments VIRTIS, VMC, ASPERA Russian scientists took part as co-investigators.
IKI RAN: http://press.cosmos.ru/na-nochnoy-storone-venery-vspleski-ozona-i-izmenchivost-dvuokisi-sery
ROSCOSMOS Press Release: https://www.roscosmos.ru/30588/
Venus Express: https://www.esa.int/Enabling_Support/Operations/Venus_Express
Images, Graphic, Text, Credits: ROSCOSMOS/ESA/Orbiter.ch Aerospace/Roland Berga.
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