The Perseverance landing site is an ancient Martian lake bottom, now it's time to find fossils of life

NASA's Perseverance probe has been studying the Jezero crater for the past eight months. The first data it sent back showed that about 3.7 billion years ago, this crater was the bottom of a large lake, receiving abundant fluids from an ancient river. Geological surveys at the Jezero crater area show that flash floods have swept the soil and rock from far away, from areas that could be at least tens of kilometers from Jezero.

NASA scientists deliberately chose Jezero crater as the place where Perseverance landed, after noticing features that suggested it could very well be an ancient lake. At the northwest corner of the hole, the team noticed a water channel radiating many branches.

Ancient lakes once existed on Mars.

This is an indication that a river once deposited alluvium in this area. Now that they have evidence that the Jezero crater is a lake bed that has been dry for billions of years , the next step is to rewrite the geological history of the large area.

' The key finding allowed us to confirm the presence of a lake, a river delta at Jezero, ' said Nicolas Mangold. Professor Mangold is the lead study author and researcher at the Nantes Planetary Geology Laboratory, France.

Extracting information from rocks

Research published earlier this month came to a conclusion thanks to images taken by Perseverance. During the first three months of wandering the Jezero region with two imaging devices, the Mastcam-Z and the Super Cam Remote Micro-Imager (RMI) , Perseverance obtained irrefutable evidence of the ancient lake.

Taking a close look at two areas 2.2 kilometers from the landing site, Perseverance saw a mound undetectable by satellites. Currently, they have the shape of a tall mound, but upon closer analysis, the team found sedimentary layers suggesting that the mound was once at the bottom of a lake in the Jezero region.

A mound called Kodiak 25 meters high contains clear evidence. A complex of layers of soil lying at a particular angle, indicating that it was once eroded by river water. ' There has never been such well-preserved stratigraphic evidence on Mars, ' said study author Mangold.

The slanted soil indicates that it once belonged to a river delta area.

The slanted soil layers are remnants of a delta region . Rivers push mud and soil into low-lying areas containing water, sediment settles over time to form alluvial mounds radiating in the shape of a propeller. The slopes below the waterline will gradually tilt and petrify over time, and that is the origin of the inclined rock layer at Kodiak mound. Wind could not create this rock structure, the cause could only be an ancient lake.

North of the Perseverance landing site is another remarkable piece of land: the layer that separates the delta from the rest of the land, about 60 meters above the bottom of the crater. Besides the slanted rock layers similar to the Kodiak site, there is a lithosphere containing stones 1.5 meters in diameter that ' can't exist on their own in this area '. According to researcher Mangold, they rolled down here following the great floods that happened in the past.

History of the Jezero . area

The rocky areas surrounding the delta tell a brief, though lacking detail, story of the once-existing Lake Jezero. The oldest sedimentary layer belongs to a river that once fed Lake Jezero.

Large floods appeared, causing the geology of the area to change. Based on analysis of the composition of large rocks, NASA confirmed they came from the highlands as far as 2.2km to the north. It is estimated that large floods move at a speed of about 6-30km/h.

Part of the ancient delta.

Ancient flash floods can occur after heavy rains, sudden snow melts due to volcanic activity or meteorite impacts. Another theory is that the giant glacier has flowed out, breaking through the natural dam.

Later, the water in the lake dried up to the point where it no longer flooded the Jezero crater. That's also when sedimentary layers began to form in the Kodiak area. The mounds in the Kodiak region vary in height, indicating that the lake's water level has experienced different highs and lows, perhaps influenced by the Red Planet's climatic conditions.

In addition to rewriting the history of the Jezero crater, the new discovery also helps scientists plan for the next missions, especially those to find rock samples to bring back to Earth for study. As for the mission to find fossils of life, Perseverance will continue to find other materials in the rock layers, looking for sediment and fossil samples that may contain traces of living organisms.