Rover footage confirms Jezero crater is an ancient Martian lake


October 11, 2021

(Nanowerk News) The first scientific analysis of images taken by NASA’s Perseverance rover has now confirmed that Mars’ Jezero Crater – which today is a dry, wind-eroded depression – was once a calm lake, regularly fed by a small river about 3.7 billion years ago.

The images also reveal evidence that the crater suffered flash floods. This flood was strong enough to sweep large boulders tens of kilometers upstream and deposit them in the lake bed, where the massive rocks are today.

The new analysis, published in the journal Science (“Perseverance rover reveals ancient delta-lake system and flood deposits in Jezero crater on Mars”), is based on images of rocks flush with the interior of the crater on its western side. Satellites had previously shown that this outcrop, when viewed from above, resembled river deltas on Earth, where layers of sediment settle in a fan-like shape as the river flows into a lake.

Images from the Perseverance rover confirm that Jezero crater is an ancient Martian lake, researchers say. This Mastcam-Z enhanced color photo mosaic shows a knoll near Jezero Crater informally nicknamed “Kodiak” by the rover team. (Image: NASA / JPL-Caltech / LANL / CNES / CNRS / ASU / MSSS)

The new images of Perseverance, taken from inside the crater, confirm that this outcrop was indeed a river delta. From the sedimentary layers of the outcrop, it appears that the river delta fed into a lake that was calm for much of its existence, until a drastic change in climate triggered episodic flooding at the end or near the end of the lake’s history.

“If you look at these pictures, you’re basically looking at this epic desert landscape. This is the most desolate place you can visit, ”says Benjamin Weiss, professor of planetary science in the Department of Earth, Atmospheric, and Planetary Sciences at MIT and a member of the analysis team. “There isn’t a drop of water nowhere, and yet here we have proof of a very different past. Something very profound has happened in the history of the planet.

As the rover explores the crater, scientists hope to uncover more clues about its climate change. Now that they have confirmed that the crater was once a lake environment, they believe its sediment may contain traces of ancient watery life. In its future mission, Persévérance will seek locations to collect and preserve the sediments. These samples will eventually be sent back to Earth, where scientists can probe them for Martian biosignatures.

“We now have the opportunity to search for fossils,” says Tanja Bosak, team member, professor of geobiology at MIT. “It will take some time to reach the rocks that we really hope to sample for signs of life. So it’s a marathon, with a lot of potential.

Inclined beds

On February 18, 2021, the Perseverance rover landed on the floor of Jezero Crater, just over a mile from its western fan-shaped outcrop. For the first three months, the vehicle stood still while NASA engineers performed remote checks of the rover’s many instruments.

Meanwhile, two of Perseverance’s cameras, Mastcam-Z and the SuperCam Remote Micro-Imager (RMI), captured images of their surroundings, including long-range photos of the outcrop edge and a formation known as the Kodiak Butte, a smaller outcrop which planetary geologists assume may have already been connected to the main fan-shaped outcrop, but has since partially eroded.

Once the rover transferred the images to Earth, NASA’s Perseverance science team processed and combined the images and was able to observe distinct beds of sediment along the Kodiak Butte with surprisingly high resolution. The researchers measured the thickness, slope and lateral extent of each layer, finding that the sediment must have been deposited by the flow of water in a lake, rather than by wind, sheet flooding or other geological processes.

The rover also captured similar sloping sediment beds along the main outcrop. These images, along with those of Kodiak, confirm that the fan formation was indeed an ancient delta and that this delta fed into an ancient Martian lake.

“Without driving anywhere, the rover was able to solve one of the big unknowns, which was that this crater was once a lake,” Weiss explains. “Until we landed there and confirmed it was a lake, it was still a question.”

Block flow

When the researchers took a closer look at the images of the main outcrop, they noticed large boulders and cobbles embedded in the youngest and highest strata of the delta. Some rocks were up to 1 meter wide and weighed up to several tons. The team concluded that these massive rocks must have originated from outside the crater and were likely part of the bedrock located on the edge of the crater or 40 miles or more upstream.

Judging from their current location and dimensions, the team says the rocks were transported downstream and into the lake bed by a flash flood that sank at up to 9 meters per second and moved up to 3,000. cubic meters of water per second.

“You need drastic flood conditions to transport such large and heavy rocks,” Weiss explains. “It’s a special thing that may indicate a fundamental change in local hydrology or perhaps the regional climate on Mars.”

Because the huge rocks are found in the upper layers of the delta, they represent the most recently deposited material. The rocks rest on layers of older and much finer sediment. This stratification, say the researchers, indicates that for much of its existence, the ancient lake was filled with a gentle-flowing river. Fine sediment – and possibly organic material – drifted along the river and settled in a gradually sloping delta.

However, the crater later experienced flash floods which deposited large boulders on the delta. After the lake dried up and for billions of years the wind eroded the landscape, leaving the crater we see today.

The cause of this climate change is unknown, although Weiss says the rocks in the delta may contain answers.

“The most surprising thing that emerges from these images is the potential opportunity to capture the moment this crater went from an Earth-like habitable environment to this desolate landscape we now see,” he says. “These rock beds may be records of this transition, and we haven’t seen this in other places on Mars.”

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