One year has passed since April 11, 2006 when Venus Express, Europe’s first mission to Venus and the only spacecraft now in orbit around the planet, reached its destination. Since then, this advanced probe, born to explore one of the most mysterious planetary bodies in the Solar System, has been revealing planetary details never caught before.
Visited extensively by several Russian and American probes from the 1960s to the early 1990s, Venus has always represented a puzzling target for scientists worldwide. Venus Express, designed and built in record time by ESA, was conceived with the purpose of studying Venus — unvisited since 1994 — in the most comprehensive and systematic way ever, to provide a long due tribute to a planet both interesting and cryptic.
Using state-of-the-art instrumentation, Venus Express is approaching the study of Venus on a global scale. The space probe is collecting information about Venus’ noxious and restless atmosphere (including its clouds and high-speed winds) and its interaction with the solar wind and the interplanetary environment. Last but not least, it is looking for signs of surface activity, such as active volcanism.
“During one year of observations, we have already collected a huge amount of data, which is exactly what we need to decode the secrets of an atmosphere as complex as that of Venus,” said Håkan Svedhem, Venus Express Project Scientist at ESA. “Analyzing it is an extreme effort for all science teams, but it is definitively paying back in terms of results.”
“Continuing at today’s rate, and on the basis of what we were able to see so far, there is no doubt that Venus Express will eventually allow a better global understanding of this planet,” continued Svedhem. “Not only will planetary science in general benefit from this, but also understanding Venus — its climate and atmospheric dynamics — will provide a better comprehension of the mechanisms that drive long-term climate evolution on our own Earth.”
New infrared data is now available about Venus’ oxygen airglow — a phenomenon detectable on the night side that makes the planet glow like a “space lantern.”
“The oxygen airglow was first discovered thanks to ground observations, and also observed by other missions to Venus such as the Russian Venera spacecraft and the U.S. Pioneer Venus orbiter,” said Pierre Drossart, co-Principal Investigator on Venus Express’ VIRTIS instrument. “However, the global and detailed view we are getting thanks to Venus Express is truly unprecedented.”
The fluorescence of the airglow is produced when oxygen atoms present in the atmosphere recombine into molecular oxygen-emitting light. But where does the oxygen come from?
“The oxygen in the atmosphere of Venus is a very rare element,” continued Drossart. “At high altitudes in the atmosphere, on the day side of Venus, the strong flux of ultraviolet radiation coming from the Sun ‘breaks’ the molecules of carbon dioxide present in large quantity in the atmosphere, liberating oxygen atoms. These atoms are then transported by the so-called ‘sub-solar’ and ‘anti-solar’ atmospheric circulation towards the night side of the planet. Here the atoms migrate from the high atmosphere to a lower layer, called the ‘mesosphere,’ where they recombine into oxygen. By doing this, they emit light at specific wavelengths that can be observed through remote sensing from Earth and with Venus Express,” added Drossart.
The detection of the airglow, and the capability to follow its evolution in time, is extremely important for several reasons.
“First, we can use the distribution and motion of these fluorescent O2 clouds to understand how the atmospheric layers below move and behave,” said Giuseppe Piccioni, the other co-Principal Investigator on VIRTIS. “In this sense, the O2 airglow is a real ‘tracer’ of the atmospheric dynamics on Venus.”
“Second, the analysis of this phenomenon will provide new clues on how its global atmospheric chemistry works — a very challenging task indeed, and still an open field of research,” continued Piccioni. “By calculating the speed at which this chemical ‘recombination’ takes place, we might be able — in the future — to understand if there are mechanisms that catalyze this recombination, and learn more about the production and recombination of the other chemical species in the Venusian atmosphere.”
“Third, the observation of the oxygen airglow allows a better understanding of the global ‘energetic’ exchange between Venus’s mesosphere and thermosphere, an even higher layer directly influenced by the Sun.”