Perseverance Mars rover uncovers the watery history of Jezero crater

Perseverance Mars rover

A selfie of the Perseverance Mars rover

NASA/JPL-Caltech/MSSS

NASA’s Perseverance rover has taken some of the most detailed measurements ever of Mars rocks, yielding insights into the lake that once filled Jezero crater.

When the rover landed on Mars in February, researchers were immediately intrigued by layered outcroppings near its landing spot in Jezero crater. The ground-penetrating radar instrument that Perseverance carries allowed it to measure the layers of rocks beneath its wheels as it drove across the Martian surface, showing that these outcroppings extended underground.

The new findings were presented by members of the mission team on 15 December at a meeting of the American Geophysical Union in New Orleans, Louisiana. “We can actually see that these layers extend down into the subsurface and go underneath the crater floor,” said Briony Horgan at Purdue University in Indiana. “We can actually trace them down.” Tracking the layers showed that they make up the oldest rocks in the crater.

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But when the rover took more detailed measurements, scraping off the surface of the rocks and looking closely at their compositions, the results surprised the researchers. “These rocks that we originally thought might be sedimentary rocks, these are in fact igneous [volcanic] rocks,” said Kelsey Moore at the California Institute of Technology (Caltech). “And even more excitingly, they’re not just igneous rocks – there’s more history to the story.”

The analysis of the rocks’ compositions revealed minerals that are generally produced by interactions between water and rock, as well as traces of two different salts that were probably left behind as salty water flowed through the cracks and pores in the volcanic rock.

The variety of minerals indicates that these rocks were probably underwater at least twice. “Two different types of liquid with two different types of chemistries points towards two different episodes of liquid water interaction,” said Eva Scheller, also at Caltech.

Studying these rocks more closely could give us a better idea of whether the lake that once – or perhaps twice – filled Jezero crater could have been habitable. “We know that specific types of minerals form under specific conditions, so if we can get a better idea of the minerals that are there… it will give us an idea of what that water looked like and whether or not it could have hosted life in the past,” said Moore. If the rover itself isn’t able to figure that out, the samples it is collecting for a later mission to return to Earth should help.

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