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A new global study of ancient Martian river beds shows that they are on average larger than the rivers of the Earth and that they previously transported large volumes of water and runoff. They also sank astonishingly recently in the history of Mars, perhaps even in the last billion years. This is a headache, given the current desert environment of the red planet, its weak atmosphere and low light. These features should have prevented vast water resources even early in world history. Scientists must now discover how both types of evidence can coexist – or prove an error.
Wet and dry river beds
Researchers at the University of Chicago, led by Edwin Kite, examined the old river beds on Mars and published their findings on March 27 in the newspaper Progress of science. The team said it was surprised to find potential evidence of a large flow of water over the last billion years.
It's been a long time since astronomers think that Mars loses its atmosphere and dries up. It is difficult to understand how a planet with so little sun and atmosphere remained warm enough to accommodate – not just a little surface water, but also fast-flowing rivers -. The researchers point out that although water may have appeared and disappeared over long periods of time, it has filled the riverbeds of the planet in more than 200 locations.
In an interview, Kite said that something else had to be wrong if the data from the riverbed were correct. Maybe the rivers are older than the researchers think. Or maybe Mars has dried up much faster than current theories suggest. But Kite says that a strange process could also keep Mars warm enough long enough for the big rivers to sink, even after the disappearance of most of its atmosphere.
"The three options are uncomfortable," says Kite. "These three solutions would require an in-depth review of our current understanding."
Kite points out that the first possibility could be explored with a sample return mission that would allow scientists to determine concrete ages for river beds that they see in orbit. Although examples of return plans are in progress, this mission is not complete. Scientists are therefore forced to explain how Mars, farther away from the Sun than the Earth, remained hot enough, even though the young Sun was even less bright than it is today. Yet the latest evidence overwhelmingly indicates that Mars was once a very humid world.
For the second option, Kite says NASA's Mars-based mission MAVEN has provided compelling evidence that the solar wind has slowly stripped the red planet of its atmosphere over a long time. The revised models will have to explain both MAVEN's atmospheric data and evidence of large amounts of recent surface water, which is a delicate balance.
The third option to keep Mars warm, even with a thin atmosphere, would depend on some kind of greenhouse warming effect. And Kite says that the most likely cause of a Martian greenhouse effect would be water ice clouds that would trap infrared light and warm Mars sufficiently for the water to stay wet and dry. moves on its surface.
Whatever the solution, the story of Mars' climate will probably remain a mystery for at least a little longer.
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