ASTRONOMERS are fairly sure that Mars was once wet. There is plenty of evidence—from dried-up river valleys to the presence of chemicals that need water to form—to suggest this. Modern Mars, though, is a freezing desert. In the 4.5 billion years since the planet came into existence, a sizeable chunk of its water has boiled away into space, another chunk is thought to have seeped deep into its interior, and what little remains on or near the surface has frozen solid. That is depressing for those who seek Martians, even bacterial ones, for most biologists agree that liquid water is a sine qua non of life.
Some researchers, though, think Mars is not entirely dry. Over the past few years evidence has accumulated that water still trickles over its surface from time to time. And a paper just published in Nature Geoscience by Lujendra Ojha of the Georgia Institute of Technology and his colleagues offers the most convincing proof yet.
In 2011 Mr Ojha, then a student at the University of Arizona, spotted dark streaks on the walls of certain Martian craters that had been photographed from orbit by a satellite called Mars...Continue reading
Source: Science and technology http://ift.tt/1LJYzyX
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