Transit may shine light on enduring mysteries of Venus

Skywatchers around the world will get a once-in-a-lifetime chance to see Venus cross in front of the sun Tuesday. The so-called transit of Venus is more than just the last such event for more than a century — it might help shed light on some of the enduring mysteries of our planetary neighbor.Strange stripes in the upper clouds of Venus are called "blue absorbers" or "UV absorbers" because they absorb blue and ultraviolet wavelengths of light. These soak up a dramatic amount of energy — nearly half of the total solar energy the world takes in. As such, they seem to play a key role in keeping Venus as hot as it is, with surface temperatures of more than 860 degrees Fahrenheit (460 degrees Celsius).One of the biggest mysteries of Venus is the "super-rotation" of its atmosphere. Violent winds drive storms and clouds around that world at speeds of more than 220 mph (360 kph), some 60 times faster than the planet rotates.
The Venus Express spacecraft the European Space Agency launched in 2005 is armed with what's called a solar occultation spectrometer "to help us pinpoint the altitude and latitude distribution for these UV absorbers and understand their behavior a bit more now," said David Grinspoon, curator of astrobiology at the Denver Museum of Nature and Science. "However, we have not yet definitively identified it. We think it's a sulfur compound, or it could be a form of elemental sulfur." Evidence of lightning on the planet was confirmed by Venus Express, even though such weather displays should be impossible there.
"You need rainfall for lightning, and we're not sure if we actually get rainfall on Venus," said Grinspoon, an interdisciplinary scientist on the Venus Express mission. "But in some ways, we don't really understand lightning on Earth very well, so by cracking how lightning works on Venus, we may understand it better here. With Venus Express, we're getting more information at the latitudes lightning's distributed in, which we hope to link with activity in the atmosphere."The Venus Climate Orbiter Akatsuki, which means "Dawn" in Japanese, was supposed to help capture vital clues about Venusian lightning with a camera dedicated to photographing it. Unfortunately, the Japanese space probe overshot the planet in 2010, although there's a chance it may still get to Venus. "It's a shame Akatsuki didn't make it into orbit around Venus — it was primed to address many questions, this matter of lightning in particular," Grinspoon said. One of the biggest mysteries of Venus is the "super-rotation" of its atmosphere. Violent winds drive storms and clouds around that world at speeds of more than 220 mph (360 kph), some 60 times faster than the planet rotates.