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Early Venus Had Oceans, May Have Been Habitable

Richard A. Lovett
for National Geographic News
October 11, 2007
 
Venus, not Mars, may have been the most likely planet in the solar system to have also developed life, scientists say.

The cloud-shrouded planet most likely started with oceans much like Earth's, which evaporated as Venus heated up, according to new research.

The oceans didn't disappear overnight, said David Grinspoon of the Denver Museum of Nature and Science.

Speaking yesterday at a meeting of planetary scientists in Orlando, Florida, Grinspoon said that preliminary results of new computer models indicate Venus may have retained its oceans for a billion years after it formed, possibly longer.

Prior models had indicated that rising Venusian temperatures had turned the oceans to steam within the planet's first 600 million years.

The extra 400 million years are even more significant than they sound, Grinspoon added, because early Venus was constantly bombarded by asteroids, reducing the likelihood of life.

The new finding suggests that the oceans existed for much longer after the asteroid bombardment tapered off.

"There may have been a sizeable interval when [Venus] was habitable," he said.

Today, however, Venus is about 100,000 times drier than Earth and is 860º F (460º C) at its surface, Grinspoon said.

(Download a wallpaper photo of a Venusian volcano.)

New Discovery From Venus

Future studies might further refine our understanding how long the planet was habitable.

If samples can be collected from the surface, for example, scientists might find rocks that formed when the planet was wet, Grinspoon said.

Determining how much water remains locked in these rocks may allow scientists to figure out how long ago the planet dried out.

Similarly, studies of Venusian gases could help scientists better estimate the rate at which water was lost into space.

Already such research is playing a role in our understanding of Venusian heating.

At the Orlando meeting, French researcher Jean-Loup Bertaux reported that the Venus Express spacecraft, now orbiting the planet, has discovered a rare form of carbon dioxide never before detected on Venus.

Instead of containing the most common form of oxygen, which has eight protons and eight neutrons, this one has one atom of oxygen with eight protons and ten neutrons.

That causes it to absorb more infrared light than normal carbon dioxide, increasing its strength as a greenhouse gas.

(See a photo of "airglow" created by oxygen in the Venusian atmosphere.)

The upsurge of interest in Venus comes hard on the heels of a recent finding that early Mars might have been colder and drier—and therefore less habitable—than previously believed.

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