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EARTHDATE: November 5, 2006

Official News - page 9

REAL LIFE NEWS: JUST HOW OLD IS VENUS?

by Hazed

Scientists are in the process of changing their minds about how old the planet Venus is. New evidence is casting doubt on the theory that the planet's surface was totally reformed during a cataclysmic bout of volcanic activity about 500 million years ago. Recent analysis carried out by scientists at the University of Minnesota has shown that this massive, destructive event probably never happened after all.

The age of a planet's surface is traditionally estimated by counting the craters. The more craters, the older the surface. Using this method, Venus at about 4.5 billion years old ought to have about 5,000 craters. Any fewer than this and processes such as weathering and geological activity have to be invoked.

But Venus only has around 1,000 visible craters, all of which are very well preserved. This led scientists to conclude that a single, massive volcanic event must have wiped out all the other craters, leaving a fresh lava coating between one and three kilometres deep over most of the planet.

Now, the researchers at Minnesota have looked again at data from the Magellan mission in the early nineties. They analyzed areas where smooth flat plains are punctuated by islands of older terrain. By considering how each island sloped off, they could estimate roughly where neighbouring islands would meet - in other words, where the base of the valley lay.

They found that the older terrain was covered by a much thinner layer of lava than had previously been thought - it was less than a kilometre thick. So the "catastrophic eruption" scenario could not account for all those missing craters.

Instead, the researchers concluded that Venus must have been resurfaced much more gradually, and that this process has left plenty of the older surface intact - and that parts of the surviving surface could be as much as a billion years old.

"The implication is that Venus on its surface preserves an extremely long record of rich geological history," Vicki Hansen said - she's one of the scientists who has done this research. "That's what's so exciting about it. It says Venus actually has a lot of secrets to tell us."

If she is right, then future missions to Venus may be able to collect and analyze rock samples from various periods throughout the planet's history - and this would give a much broader picture of the planet's evolution.


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