18 December 2007
However, while water abounds on Earth, Venus is a hellish place where the surface is the temperature of molten lead. Why did the two planets take such different evolutionary paths? This is one of the questions the Venus Express mission is seeking to answer.
Follow the oxygen
To understand how Venus evolved, scientists designed Venus Express’s instruments to peer deep inside its atmosphere. The gases cloaking the planet are a record of its turbulent past. For example; the VIRTIS imaging spectrometer—whose high-resolution channel was developed by the Observatoire de Paris—has measured oxygen emissions at the top of Venus’s atmosphere, on the night side of the planet.
This oxygen can only be coming from the day side of Venus, where the Sun’s ultraviolet rays break down carbon dioxide (CO2)—the main constituent of its atmosphere—thus freeing oxygen. “Finding oxygen on the night side of Venus has told us a great deal about the circulation in the upper reaches of its atmosphere,” said a delighted Pierre Drossart, VIRTIS Co-Principal Investigator.
Compressed atmosphere
This high-altitude atmospheric circulation is also the reason for another paradoxical phenomenon detected by Venus Express’s SPICAV instrument. On Venus’s night side, where temperatures should normally be the coldest, SPICAV has observed a layer of the atmosphere between 90 and 110 km where in places the temperature is 70°C higher than expected.
The explanation is fairly simple: if you’ve ever inflated a bicycle tyre, you’ll have felt the hot compressed air as it shoots out of the pump. This is exactly what is happening with the compressed gases in Venus’s atmosphere.
“We have calculated that for the atmosphere to heat this much, the gases transported from the day side to the night side must sink at a rate of 50 cm per second, which is surprisingly fast,” enthuses Jean-Loup Bertaux, SPICAV Principal Investigator.
“We have calculated that for the atmosphere to heat this much, the gases transported from the day side to the night side must sink at a rate of 50 cm per second, which is surprisingly fast,” enthuses Jean-Loup Bertaux, SPICAV Principal Investigator.
Where did all the water go?
Venus Express’s ASPERA instrument has confirmed that part of Venus’s atmosphere is being stripped away by the solar wind, and that the gases escaping are mostly hydrogen and oxygen—two atoms of hydrogen for every one atom of oxygen.
Interaction between Venus and the solar wind. Crédits : ESA
“Exactly the same ratio as in the water molecule, H2O,” explains Jean-André Sauvaud, ASPERA Co-Principal Investigator.
In the 15th century, Botticelli depicted the goddess Venus emerging from the water in one of the most famous paintings of the Renaissance, The Birth of Venus. As Venus Express has now shown us, in the real world the exact opposite is true.
