Scientists have confirmed in a new study that the scientific playground of NASA’s Perseverance Mars rover — Jezero Crater — was once home to an ancient lake.

New radar data from one of Perseverance’s instruments revealed layers of sediments that, billions of years ago, sat at the bottom of a Martian lake like the material that settles at the bottom of Earth’s oceans. Though it’s no longer a wet environment, the former lakebed reveals itself through stratified sections sandwiched throughout the 65 feet below the rover’s six wheels.

“Imagine a very still pond where nothing much happens except fine layers of muck are laid down every year. That’s the sort of situation we think we’re seeing with these radar signatures,” David Paige, the deputy principal investigator of the instrument behind the discovery: Perseverance’s Radar Imager for Mars’ Subsurface Experiment (RIMFAX), told Inverse.

The planetary scientist is also the lead author of the new study, published today in the journal Science Advances, describing the ancient wet Martian landmark.

The lake may have been about the size of two Manhattan islands arranged the long way and would have sat inside the 28-mile-wide Jezero Crater. According to Paige, the lake depth would have varied depending on climatic conditions.

How did Perseverance find these layers?

“What’s exciting about the results that we’re showing is that there are a bunch of very fine, regular layers, and they are not tilted. These are exactly the type of layers you’d expect to be laid down in a lake,” Paige says. Water has a low viscosity, so it settles in a flat, horizontal way. Think of holding a glass of water and how the water line remains parallel to the ground no matter how harshly you angle the cup.

Paige says that radar, like that on RIMFAX, works by producing images of what’s deep below the surface. Like all images, the viewer relies heavily on context to make conclusions about what they see.

Equipped with knowledge about Earth-based radars and the images they create, Paige and the team conclude what they are seeing is the result of an ancient river carrying and depositing Martian material it brought downstream and left behind inside Jezero Crater.

What lies beneath?

For the past three years, Perseverance has roamed back and forth along the crater floor to answer all the questions the NASA science team assigns it to investigate. For this subsurface study, RIMFAX fired radar waves downwards every 10 centimeters that the rover traversed along the western crater edge near what looks like an ancient river delta.

What lies beneath, revealed in RIMFAX observations obtained from May 10 to December 8, 2022, is one more page in the unraveling story of Mars.

Mars is a fabulous target for astrobiologists. It’s 140,000,000 miles away, a relatively short distance when compared to other worlds that might harbor life.

Life needs water. If Mars once had liquid water plus other hospitable qualities — like a magnetic field that would have shielded the surface from cosmic rays, for instance — then perhaps the Red Planet could have supported life.

As far as we know, nothing calls Mars home nowadays. The verification that Jezero Crater was home to an ancient lake does, however, mean that NASA picked a great spot on all of Mars to investigate ancient traces of alien life.

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