Mineral may unlock secrets of Venus's ancient oceans

Did ancient oceans on Venus last long enough for potential life to have emerged? The answer could be locked inside a hardy mineral called tremolite, which future robotic missions to our neighbouring planet could find and study.

The surface of Venus today is extremely dry and hot enough to melt lead. But there is evidence that the planet was much cooler and wetter in the past, before a runaway greenhouse event probably evaporated any oceans the planet had.

In fact, previous research has suggested that the formation of clouds could have slowed this greenhouse effect, allowing oceans to survive for 2 billion years or more.

"For half of its lifetime, Venus could have been a habitable planet with liquid water oceans," says planetary scientist David Grinspoon of the Denver Museum of Nature and Science in Colorado, US.

If so, chunks of rock ejected by asteroid or comet impacts could have shuttled living organisms between Earth and Venus, he says. "Earth life could have been transplanted to Venus and it would have landed on a wet planet," he told New Scientist. "Conversely, it's even possible that Earth life came from Venus."

Chemical clock

Most of the planet's surface appears to have been covered over with lava, obscuring records of Venus's history, and making it difficult to determine how long any oceans might have lasted - a crucial factor in determining whether life could have emerged there.

But Grinspoon and fellow planetary scientist Mark Bullock of the Southwest Research Institute in Boulder, Colorado, US, say there is reason for hope. A hardy water-bearing mineral called tremolite could be the key to unlocking Venus's past, they say.

Experiments by Natasha Johnson of NASA's Goddard Space Flight Center in Greenbelt, Maryland, and Bruce Fegley Jr of Washington University in St Louis, Missouri, both in the US, have previously shown that tremolite, which forms in the presence of water, is tough enough that it could have survived on Venus's surface to the present.

Grinspoon and Bullock believe tremolite can be used as a kind of chemical clock. Because researchers know how long tremolite takes to decompose into other minerals in the extreme temperatures on Venus, tremolite abundances could be used to determine how long ago the rocks containing it were formed, and thus how recently water was present on Venus's surface.

High ground

Future robotic landers could look for tremolite, Grinspoon says. Although robots would not last long on the blisteringly hot surface, a couple of hours would suffice to measure it using modern instruments, he says. He thinks such a mission is unlikely in the near future, but very likely in the next 10 to 20 years.

Ellen Stofan of University College in London, UK, says she is optimistic about the prospects for finding evidence of an older, wetter Venus, despite the lava flows covering much of the surf

•	Mineral may unlock secrets of Venus's ancient oceans NewScientist.com (UK), Wednesday, Oct. 10, 2007 Byline: David Shiga, NewScientist.com news service