NASA model suggests ancient Venus cooler, habitable

A computer rendition showing the model land-ocean pattern of Venus.
A computer rendition showing the model land-ocean pattern of Venus.

For a 2 billion-year span that ended about 715 million years ago, Venus was a much more pleasant spot than it is today, scientists say. To observe Venus now is to witness a dry and toxic landscape, where the planet heats up to a scorching 864 degrees Fahrenheit. A super-strong electric wind is believed to sweep the smallest traces of water into space.

But travel back in time a few billion years or so. Ancient Venus, according to a new computer model from NASA, would have been prime solar-system real estate, possibly even downright habitable.

To support life, Venus would have needed much balmier temperatures and a liquid ocean -- which is a significant if, though elemental traces like deuterium indicate water existed on Venus at one point.

Venusian temperatures, too, appear to have been far cooler when the solar system was younger. NASA's Goddard Institute for Space Studies, in a report published last week in the journal Geophysical Research Letters, calculated that the average surface temperature 2.9 billion years ago was about 50 degrees Fahrenheit. That would have made Venus, surprisingly for a planet closer to the sun, a bit chillier than Earth was at the time.

To determine the ancient temperatures of Venus, NASA scientists applied a computer model similar to the ones used to predict the future of Earth's climate. The simulations relied on topographical data from the Magellan mission, a spacecraft that in the early 1990s mapped 98 percent of the surface of Venus with radar.

"Many of the same tools we use to model climate change on Earth can be adapted to study climates on other planets, both past and present," said Michael Way, a Goddard researcher and the lead author of the new study, in a press release. "These results show ancient Venus may have been a very different place than it is today."

Old Venus would have orbited a sun about 30 percent dimmer than today. The institute's simulation revealed that, when Venus' extremely slow daily rotation is taken into account, unusual weather patterns emerge. (Venus rotates so slowly -- 243 Earth days per spin -- it actually completes an orbit of the sun before its day is over. That is, a Venusian year -- about 225 Earth days long -- is shorter than Venusian a day. Were there to be a shallow ocean on Venus at the time, the sun would have churned some of the liquid sea into a thick cloud layer. The net effect would have been like the flap of foil across a car windshield.

Those ancient Venusian clouds would act "like an umbrella to shield the surface from much of the solar heating," said the institute's Anthony Del Genio in the press release. "The result is mean climate temperatures that are actually a few degrees cooler than Earth's today."

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