Perseverance discovers how Lake Mars disappeared

Image credit: NASA / JPL-Caltech / ASU / MSSS 

“If you want to go to Mars in search of indirect clues of past biological activity, you have to go to Jezero. We know it was a lake and this fact makes it very suitable for life.” These are the words of Jorge Pla-García, a member of NASA’s Mars 2020 Perseverance mission, for Diario AS moments before the Perseverance rover landed on the red planet.

Just that area, the Jezero crater, was about 3.7 billion years ago a lake fed by a small river, according to the analysis of the images taken by the NASA rover, published in the journal Science. The images reveal that millions of years ago this area suffered great flash floods, which caused the movement of rocks from several kilometers away, and that they ended up in the lake, where they are today.

This new analysis is based on the study of images of rocks that emerge inside the crater, on its western side. Previously, through satellites, this outcrop had been verified seen from above, which announced a similarity with the deltas of terrestrial rivers, in which the sediment layers are deposited in a fan shape while the river feeds from a lake .

River delta
The new images unequivocally reveal that this area was once a river delta. Taking the sedimentary layers as a reference, everything indicates that the river delta fed a lake that was calm for much of its existence on Mars. Until one day, a strong change in the climate wiped out it, through repeated flooding towards the end of its history, NASA explains.

“If you look at these images, you are basically looking at this epic desert landscape. It is the most desolate place you can visit. There is not a drop of water anywhere and yet here we have evidence of a very different past. Something very profound happened in the history of the planet, “says Benjamin Weiss, professor of planetary sciences in the Department of Earth, Atmospheric and Planetary Sciences at MIT.

Remote scan
The Perseverance rover reached Mars on February 18 of this year, at a distance of just over a kilometer from the western outcrop of the Jezero crater. And although in the first three months it was stopped (while NASA engineers carried out various checks), two of its cameras did not stop working.

The Mastcam-Z and the SuperCam Remote Micro-Imager (RMI) took graphical evidence of the environment, with long-distance photos of the edge of the outcrop and a formation known as the Kodiak butte, a smaller outcrop than geologists believe could have been. connected to the main, but partially eroded.

After sending them to Earth, the scientists processed and combined them, verifying the existence of different sediment beds on Mount Kodiak. After making several measurements, of thickness, slope and lateral extension, they discovered that these sediments must have been deposited by the flow of water in a lake, and not by the wind, or other geological processes. The rover also captured sloping sediment beds in the main outcrop. Together with those of the Kodiak, they confirmed that it was an ancient delta that fed a Martian lake.

Solved one of the great unknowns
According to Weiss, the NASA rover managed “without getting anywhere, to solve one of the great unknowns: that this crater was once a lake. Until we actually landed there and confirmed it, it was always a mystery.” Looking more closely at the images, they found that there were large rocks embedded in the younger and upper layers of the delta, up to a meter wide and several tons in weight.

According to experts, they must have come from outside the crater, possibly they were part of the rocky bed at the edge of the crater, or they were about 40 miles upriver. Due to their location and dimensions, they consider that they were washed away by the river and into the lake after a sudden flood, which flowed up to 9 meters per second and moved 3,000 cubic meters of water per second. “Brisk flood conditions are needed to transport such large and heavy rocks. It is something special that may be indicative of a fundamental change in the local hydrology or perhaps the regional climate of Mars,” says Weiss.

The next step
Now, the rover will continue with the study of the Jezero crater, with the future taking of sediment samples, in which they could find signs of ancient aquatic life on the planet. The samples will be sent to Earth for further analysis. “Now we have the opportunity to search for fossils. It will take some time to get to the rocks that we really hope to sample for signs of life,” concludes Tanja Bosak, member of the research team and associate professor of geobiology at MIT.