Today's Venus Transit Could Illuminate Mysteries of Venus

Venus Pioneer Orbiter — NASA’s Pioneer Venus Orbiter took this false color image of Venus’ clouds during its mission circling the cloudy world from 1979 into 1992. Some scientists have speculated that the planet’s clouds might be a cozy habitat for microbial life.

(Image credit: NASA/GSFC)

Skywatchers around the world will get a once-in-a-lifetime chance to see Venus cross in front of the sun today (June 5). 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.

Bizarre stripes on Venus

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).

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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."

"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.

The long-vanished oceans of Venus are thought to have been culprits of what is called a runaway greenhouse effect. Scientists think that planet's close proximity to the sun heated its water, causing it to build up in Venus' atmosphere as steam. Water is a greenhouse gas, trapping heat from the sun that would have vaporized still more water, a vicious cycle that heated Venus enough to boiled away its oceans.

Charles Q. Choi is a contributing writer for Live Science and Space.com. He covers all things human origins and astronomy as well as physics, animals and general science topics. Charles has a Master of Arts degree from the University of Missouri-Columbia, School of Journalism and a Bachelor of Arts degree from the University of South Florida. Charles has visited every continent on Earth, drinking rancid yak butter tea in Lhasa, snorkeling with sea lions in the Galapagos and even climbing an iceberg in Antarctica.