It has been an eventful few days for the Venus Express spacecraft.
After entering orbit around its target planet on Tuesday, the observatory turned on its instruments and snapped the first images ever taken of the swirling atmosphere above the Venusian south pole on Wednesday.
The European Space Agency released two false-colour images taken by the spacecraft’s Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) and Venus Monitoring Camera (VMC) on Thursday.
The striking VIRTIS image shows the planet split into a day and night side. The day side shows a composite picture of various wavelengths capturing mostly sunlight reflected off the tops of clouds.
The more dramatic night side, taken in the infrared, features a large vortex of clouds spiralling in toward the pole. In this half of the image, the brighter areas indicate thinner clouds, as these allow more thermal radiation from below to shine through. The darker features show thicker clouds.
Kevin Baines, a VIRTIS co-investigator from NASA’s Jet Propulsion Laboratory in California, US, likens the radiation Venus produces about 20 km above the surface to a glowing flashlight shining up at the atmosphere. “What we’re doing here is we’re backlighting the atmosphere – we’re seeing silhouetted clouds,” he told New Scientist.
Scientists are particularly intrigued by the very dark feature near the bulls-eye of the pole, where the planet’s rapid, 200 mph (320km/h) global circulation seems to spiral to an end point.
VIRTIS co-investigator Fred Taylor, at the University of Oxford, UK, says he was surprised by the different morphology of the south pole vortex as compared with the “double hurricane” structure seen by NASA’s Pioneer Venus mission at the north pole. Because Venus is not tilted off its rotation axis, scientists expected the planet to be symmetrical about the equator.
But these are only the first images and the cloud structures may well change with time. “Now we see such great detail that we can watch Venus over time and see all the cloud filaments move around,” Baines says. “And we’ll start measuring winds in much more detail than we ever have in the past.”
Mark Bullock, at the Southwest Research Institute in Boulder, Colorado, says he has been “really blown away” by the quality of first VIRTIS image, considering it was taken at an altitude of 206,452 km. “Clearly this instrument is performing well,” he says.
Venus Express scientists hope to make sense of some of the planet’s unusual behaviours, which could in turn shed some light closer to home. Venus is considered Earth’s sister planet gone awry. Its atmosphere rotates many times faster than the planet itself for unknown reasons. And its meteorology is dominated by a runaway greenhouse effect.
Taylor says it will take time for scientists to work out what is going on in the images returned by Venus Express. But for now, he says, “the exciting thing is that we are definitely back in the Venus exploration business”.