Most promising clue yet there may have been life on Mars
A raging river might have cut across Mars billions of years ago.
The Perseverance rover has captured new images that appear to reveal geologic evidence of a fast-flowing river that fed into Jezero Crater, the site of an ancient Martian lake.
Perseverance began exploring the remnants of the environment within the crater, which now resembles a dry lake bed, after landing on the red planet in February 2021.
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The rover started studying a fan-shaped deposit in the area that stands 250 metres tall, likely the remnants of an ancient river delta, about a year ago.
First, Perseverance studied the eroded front edge of the fan. Now, the rover has climbed on top of the fan to explore the sedimentary rock that may preserve evidence of past water – and life, if it ever existed.
"This fan really represents the main history of water in the crater," Katie Stack Morgan, Perseverance's deputy project scientist at NASA's Jet Propulsion Laboratory, told CNN. "With the rover, we're actually moving through different environments that once had water associated with them. So here in Jezero, we have evidence of lakes, deltas and ancient rivers."
The curved layers of the fan suggest flowing water shaped them, and the latest images taken by the rover point to a deeper and more rapidly moving river than scientists expected on Mars. It's the first time scientists have seen environments such as this on Mars.
Scientists have long been curious about the diverse types of waterways that once existed on Mars more than three billion years ago, when the planet was warmer and wetter. Previous observations by the Curiosity rover, which landed on Mars in 2012 and is exploring Gale Crater about 3,700 kilometres away, revealed evidence of shallow streams rather than powerful rivers.
Perseverance's latest findings, collected in two mosaic images, showcase cobbles and coarse sediment grains.
"Those indicate a high-energy river that's truckin' and carrying a lot of debris. The more powerful the flow of water, the more easily it's able to move larger pieces of material," said Libby Ives, a postdoctoral researcher at JPL, in a statement.
Rivers likely carried the big boulders and debris from other areas on Mars to Jezero Crater, Morgan said.
Clues within the new Mars mosaics
One of the mosaics shows a deposit dubbed "Skrinkle Haven," where flowing water carved rock layers that remain billions of years later. Scientists aren't sure whether the rows of rocks that appear to ripple across the landscape are like the shifting riverbanks of the Mississippi or the island-like sandbars of the Platte River in Nebraska.
The rocky layers were likely much taller in the past but have been eroded by wind over time.
"The wind has acted like a scalpel that has cut the tops off these deposits," said Michael Lamb, river specialist and Perseverance science team collaborator at Caltech, in a statement. "We do see deposits like this on Earth, but they're never as well exposed as they are here on Mars. Earth is covered in vegetation that hides these layers."
Perseverance also observed "Pinestand," an isolated hill formation filled with layers of sandwiched sedimentary rocks that curve toward the sky as high as 20 metres.
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"These layers are anomalously tall for rivers on Earth," Ives said. "But at the same time, the most common way to create these kinds of landforms would be a river."
Perseverance and the search for life
Scientists are using all the tools in Perseverance's kit to get to the bottom of the river mystery, including the rover's ground-penetrating Radar Imager for Mars' Subsurface Experiment, or RIMFAX, to search below the site. The Perseverance team is also analysing other images taken by the rover.
Samples of rocks and dirt collected by the rover will eventually travel to Earth via the ambitious Mars Sample Return program, a series of successive missions slated for the next decade that will venture to the red planet, grab samples from Perseverance's cache and bring them back for scientists to analyse in labs around the world.
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"One of the reasons why we chose Jezero as the landing site is because the more diverse rocks we have, the more chance we have to learn more about the processes that took place on Mars and formed Mars," Morgan said. "We have different types of potential habitable environments recorded within these rocks."
The rocks and Martian soil samples might reveal whether life ever existed on Mars.
"To answer that question, we have to bring these rocks back to Earth, where we have really sophisticated instruments and laboratories that can deeply probe that question," Morgan said. "And it's a hard question to answer. We struggle even with early Earth rocks to answer this question. But Perseverance's job is to identify those rocks that have the best chances of having life in them, and we've been able to do that."
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