Venus, along with two co-stars, put on a great show earlier this week. But she's not finished. She appears in the ultraviolet and infrared in the pages of this week's issue of the journal Nature, courtesy of researchers with the European Space Agency's Venus Express orbiter.
The images are giving scientists a unique window on the torrid planet's atmosphere. It's one of many aspects of Earth's twin that scientists are exploring. They are trying to piece together the story of how two such closely related orbs could evolve such dramatically different surface environments.
Twins, he says? Earth and Venus are roughly the same size. But Venus is shrouded in clouds made largely of droplets of sulfuric acid. Its atmosphere is 93 percent carbon dioxide. This has set up a runaway greenhouse effect that keeps temperatures on the planet at a toasty 890 degrees Fahrenheit. Another contribution to the high heat: The planet's "day" is 243 Earth days long – a planetary version of a holiday roast slowly turning on a spit. To top it off, on Venus the sun rises in the west and sets in the east. So, think fraternal twins.
At ultraviolet wavelengths, as in the image to the left, the clouds show detailed patterns of light and dark. The dark patches represent a mysterious chemical or set of chemicals that absorb ultraviolet light.
The infrared information gives scientists a measure of cloud height and how temperatures change with altitude.
By combining information from these different wavelengths of light, Dmitry Titov, with the Max Planck Institute for Solar System Research in Lindau, Germany, and colleagues have been able to tease out a trio of broad atmospheric features above the planet's southern hemisphere.
From the equator to about 50 degrees south, clouds top out at a fairly consistent 23,600 feet. Convection – the same kind of process that triggers the growth of thunderheads on Earth in the summer – appears to be drawing the mystery chemicals up high to generate the patterns in the ultraviolet image.
From 50 degrees south to 70 degrees south, the cloud tops appear to spread smoothly, thanks to a fairly steady flow of winds. Temperatures are cool enough up there to allow a haze of sulfuric acid to form, masking the signature of any mystery material still welling up through the atmosphere. That amount is likely to be small. Unlike temperatures at low latitudes, here temperatures appear to fall with depth, rather than rise. This stifles convection.
At the pole, a dark ring in the ultraviolet signals a strong, hurricanelike vortex of winds whipping around the planet once every 2.5 Earth days. At the center of this high-speed vortex, cloud tops are lower, reaching a height of about 21,000 feet.
Researchers point out that many of the processes they are seeing on Venus are amped-up versions of similar processes on Earth.
The orbiter, which arrived at Venus in April 2006, is in its first overtime period. Its initial operating period covered 500 Earth-days of observations. But in February 2007, mission managers approved an extension that will keep the craft swinging around Venus until May 2009.
Photo Credit: ESA/MPS/DLR/IDA