New evidence that Jezero Crater on Mars was a lake

Photo of the area where a river delta entered the lake that existed in Jezero Crater (Image NASA/JPL-Caltech/ASU)
Photo of the area where a river delta entered the lake that existed in Jezero Crater (Image NASA/JPL-Caltech/ASU)

An article published in the journal “Science Advances” reports new evidence that Jezero Crater on Mars was a lake when the red planet was young and much more Earth-like. A team of researchers coordinated by UCLA (University of California at Los Angeles) and the University of Oslo used data collected by the RIMFAX radar (Radar Imager for Mars’ Subsurface Experiment) mounted on NASA’s Mars Rover Perseverance, exploiting its ability to carry out detections underground to a depth of 20 meters.

Data collected between May 20 and December 8, 2022, in a contact area between the crater floor and the delta of an ancient river, made it possible to map that area and reconstruct the sequence of erosions and sediment deposits. Conditions were favorable for the development of life forms and there may still be traces of them in the samples collected by Perseverance.

Since it landed on Mars on February 18, 2021, the Mars Rover Perseverance has been exploring Jezero Crater, chosen precisely for its geological characteristics considered very interesting, among others, by some targeted studies conducted by other researchers. It’s hardly a surprise that this ancient crater created by a meteorite impact was filled with water for some time.

The conditions of the time allowed liquid water to be present on the Martian surface with oceans, seas, lakes, and rivers. When the lake in Jezero Crater began to dry up, sediment carried by a river formed a delta in the lake. Eventually, the lake dried up and the sediments eroded away, leaving geological traces still visible on the surface.

In searching for more evidence of that lake and reconstructing the geological history of Jezero Crater, the Mars Rover Perseverance used its RIMFAX radar to probe the subsurface. This allowed to reach the base of the sediments and reveal the surface of the now-buried crater floor.

It took months of detections between May 20 and December 8, 2022, to obtain the data necessary for this study. The long period of survey and another long period spent analyzing the data collected bore fruit, bringing the new confirmation of the existence of that ancient lake.

The reconstruction shows two distinct periods of sediment deposition alternating with two periods of erosion. The crater floor beneath the delta isn’t uniformly flat, suggesting that a period of erosion occurred before the lake sediments were deposited. Radar images show that the sediments are regular and horizontal, just like the sediments deposited in lakes on Earth.

A second period of sediment deposition occurred when fluctuations in the lake level allowed the river to deposit a large delta that once extended well into the lake but subsequently retreated closer to its mouth.

UCLA’s David Paige, the principal investigator of the RIMFAX instrument and one of the authors of this study, explained that the changes he and his colleagues see in the geologic traces were caused by large-scale changes in the Martian environment. When it was young, Mars had an Earth-like environment that was very dynamic until an environmental collapse started transforming it into the barren red planet we know.

These new results confirm that Jezero Crater is very interesting, also for astrobiologists given that the conditions were favorable for the emergence of life forms. However, to have more in-depth analyzes, it’s necessary to bring samples back to Earth. NASA and ESA have been developing a collaboration for the Mars Sample Return program for some years but costs and technical difficulties led NASA to stop work to reevaluate the project.

Other nations are developing projects to bring Martian samples back to Earth, and China, for example, is making continued progress in its space program. However, the Mars Rover Perseverance already collected samples in various areas of Jezero Crater while independent missions would also need to collect samples to bring back to Earth. In any case, whatever happens, it will take several years before anyone can conduct analyzes of samples that contain potential traces of ancient Martian life forms.

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