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Source：Charm Information Network Editor：Science Time：2025-06-25 23:26:34

Back in 2011,Watch Power NASA scientists announced they had spotted compelling evidence that water sometimes still flowed on Mars. Now, researchers are backpedaling on these watery conclusions.

To NASA's credit, the 2011 evidence looked quite convincing. Images captured by the Mars Reconnaissance Orbiter — a NASA satellite orbiting Mars — showed telltale dark streaks running down various mountains, valleys, and craters on Mars. They look strikingly similar to features formed on Earth's surface by flowing water.

But, according to a new study in the journal Nature Geoscience, it turns out these dark streaks are made mostly of "granular flow" — sand and perhaps rocks falling downhill — rather than water flowing down valleys during the warmer Martian summers.

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Researchers came to this conclusion after examining new images and topographic data taken by the Mars Reconnaissance Orbiter.

The dark streaks "grow gradually over a month and reappear on an annual basis," Colin Dundas, a planetary geologist at the U.S Geological Survey and the study's lead author, told Mashable. "It resembles the behavior of liquid water."

Original image has been replaced. Credit: Mashable

"Granular flow is the large part of what’s going on rather than liquid water," Dundas added.

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NASA has identified thousands of these dark, flow-like streaks on the Martian surface. In this study, Dundas and his team examined over 150 of these features at 10 different Mars locations.

NASA is attempting to figure out if Mars might be a good environment for any hardy microbial critters. But these new results don't exactly bolster chances that life still exists on Mars.

"On Earth, water and life often go together," said Dundas. "If on Mars there's little or no water, that’s a challenge for Earth-like life."

Original image has been replaced. Credit: Mashable

Dundas, however, notes these drier environs don't necessarily eliminate the possibility — however slight — that life can exist somewhere on Mars.

"That's not ruled out," he says, "but we're filling out an understanding of the present conditions."

And although the dark streaks seem to be made from mostly sandy soil, some water could still play a role in triggering these sand flows on Mars, explains Dundas. How much water is involved, if any, still remains unknown.

"They’re a puzzling feature on Mars," says Dundas. "And there are still pieces of the puzzle that we don’t understand."

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