Mars Rounded Pebbles: Do Rocks Discovered By NASA Indicate An Ancient River?
Rounded pebbles found on the surface of Mars provide evidence that water once flowed on the planet, according to a new study published in Science.
The Martian pebbles were discovered in pictures taken by NASA's Curiosity rover, which found densely packed pebbles in several areas. Researchers analyzed photos of 515 stones, concluding that the size and rounded shape indicate rocks which traveled in water, perhaps in the kind of river that isn't able to exist in the cold, arid climate of modern day Mars.
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"We know it was a streambed because it takes a fast flow to move pebbles of this size, and they're rounded," said Dawn Sumner, a University of California, Davis researcher and co-author of the study. "The rounding requires that they're banged against each other and the sand a huge number of times to break the edges of the rocks. It's like how you polish rocks in a polisher, you hit them against each other over and over."
Sumner added that the rocks -- which were rounded by fluvial abrasion, to use the technical term -- are believed to be at least two billion years old. Given the kind of pebble-rounding researchers saw, Sumner says that the ancient stream must have flowing "for a long period of time over a long distance."
"You aren't going to get rounding with transient water or a flash flood," Sumner said.
Another way you aren't going to get that rounding is from wind abrasion. Rocks worn down by wind would be more rough and angular than the rounded pebbles on Mars are.
Finding the rounded pebbles wasn't a result of serendipity: the main reason NASA chose to land the Mars rover between Gale Crater and the base of Mount Sharp was to study layered rocks there.
'We knew there was an alluvial fan in the landing area, a cone-shaped deposit of sediment that requires flowing water to form," said Sumner. "These sorts of pebbles are likely because of that environment. So while we didn't choose Gale Crater for this purpose, we were hoping to find something like this."
The discovery of the round pebbles is the latest evidence of the possibility of water -- and life -- on Mars. In 2004, NASA's Spirit and Opportunity rovers found soil that had been exposed to water, and in 2008, the Phoenix Mars Lander uncovered the existence of current water-ice.
Here on Earth, scientists recently found a bacteria living in the Canadian arctic permafrost, in conditions previously thought to be totally inhospitable to any kind of life. The findings led the scientists to wonder whether similar bacteria could exist in the harsh climate of Mars.
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