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Rover finds evidence of ancient flash floods on Mars, researchers say

Scientists confirmed the Jezero crater once contained a lake. They were surprised to find evidence of flooding so intense it could move large boulders.
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The Perseverance rover, which spent months traveling to Mars, could hardly have landed in a more interesting spot. 

The Jezero crater — a dry, wind-scoured patch of Martian rock where the rover touched down in February — was once a lake bed fed by an ancient river with floods so powerful they could move boulders, scientists say. 

Those findings, published last week in the journal Science, confirmed scientists’ suspicions that the crater contained a lake millions of years ago, and also suggests that this part of Mars had a warm, humid past with a more complicated water cycle than was known. 

“There were rushing rivers here,” Katie Stack Morgan, a deputy project scientist of the Mars 2020 project and an author of the paper, said of Jezero’s landscape some 3.5 million years ago. “Jezero might have been a good place for life to exist and that environment evolved over time.”

Further studies could help researchers understand why the planet dried out and provide new clues about whether the planet once supported life. 

A view from the ground

New perspective — thanks to Perseverance — and geological detective work by scientists made these insights possible. 

The rover, which transmitted imagery from the crater’s surface back to Earth, provided scientists new views that couldn’t be seen from space.

“What you think you’re seeing from orbit around Mars may not be what you see when you get into the crater at eye level,” Stack Morgan said.

The surface-level images supported scientists’ theory that Jezero once featured a deep lake. 

The images also gave scientists, including the 39 authors of the Science paper, the ability to further analyze the layers of a rock on an outcropping called Kodiak. Researchers found those layers were consistent with how river deltas appear on Earth, suggesting water flowed into the ancient lake. 

But the visuals also contained a few surprises. On other cliffs near Kodiak, the scientists noticed large boulders — some as wide as five feet across and shaped by water — within upper layers of the formations, according to the Science paper.

They suspect the boulders were deposited during massive flash flooding events powerful enough to rapidly transform the Martian watershed. 

They don’t know what caused these floods, but speculated in the paper that intense rainfall, rapid snowmelt or changes to glacier ice could have sent floodwaters raging. 

“It could be very difficult to reconstruct that kind of thing,” Stack Morgan said.

Looking for signs of life

Perseverance is the first rover to collect and cache Martian rock samples. 

Stack Morgan said it’s exciting to know with certainty the rover will visit and collect samples from an ancient lake that was fed by a river.

That means the rover will have access to a diversity of rock types that were deposited to the crater. The rover also should be able to reach and sample portions of ancient lake beds, which are “exactly the kind of beds on earth that are great for organic material and biosignatures," she said.

The rover could be in the right place to answer some of humankind's deepest questions.

“That’s why we came to Jezero with Perseverance,” she said. “So far, Jezero has not disappointed.”