23 November 2010
Sulphuric acid mist
“Venus’ atmosphere is very rich in sulphur dioxide, but nobody expected to find any this high up,” says Jean-Loup Bertaux, Principal Investigator for the SPICAV instrument at the LATMOS2 atmospheres, environments and space observations laboratory. Even models developed by the team in California led by Professor Yung, a specialist in atmospheric chemistry, didn’t predict its presence.”
Sulphur dioxide (SO2)—the reason for the thick layer of sulphuric acid clouds blanketing Venus—has been detected in the planet’s upper atmosphere, at an altitude of 90 to 110 km.
How? By the Venus Express spacecraft, and more especially by the SPICAV spectrometer developed with CNES support.
SPICAV uses the solar occultation method,” explains Jean-Loup Bertaux. “We wait for the Sun to set and we then analyse solar radiation through the planet’s atmosphere. Because SO2 partly absorbs ultra-violet radiation, we can obtain a very good vertical distribution.”
Scientists believe that the SO2 in Venus’ upper atmosphere is coming from sulphuric acid mist. At altitudes of 90 km and higher, temperatures are high enough for sulphuric acid to evaporate and be broken down into SO2 by solar radiation.
New ways to cool Earth
While it’s true that Venus is a long way off, in fact the same type of phenomenon occurs here on Earth,” enthuses Jean-Loup Bertaux.
Erupting volcanoes spew SO2 into the atmosphere, to altitudes of around 20 km, where it forms droplets of sulphuric acid. These droplets reflect a large proportion of solar radiation back into space, cooling Earth like a parasol.
For example, when Mount Pinatubo erupted in the Philippines, Earth’s surface temperature dropped by 0.5°C.
This has led Paul Crutzen, the Nobel Prize for Chemistry, to put forward the idea of injecting large quantities of SO2 into the atmosphere artificially to cool Earth’s surface and counteract the increasing greenhouse effect. “It’s an interesting solution, but we need to look at it carefully from every conceivable angle,” says Jean-Loup Bertaux.
“We can’t predict what will happen from modelling alone. We also need to experiment, and with Venus we have a great testing ground, since there are very large quantities of sulphuric acid droplets in its atmosphere. That’s why studying Venus is also very relevant to Earth,” concludes Bertaux.
1 From the California Institute of Technology, the University of Michigan, Academia Sinica and the National Central University of Taiwan, and LATMOS (CNRS/UMPC/UVSQ).
2 Laboratoire ATmospheres, Milieux, Observations Spatiales.