Confirmation of ancient lake on Mars raises hope that soil and rock samples from Perseverance rover contain traces of life

If life ever existed on Mars, the Perseverance rover’s verification of lake sediments at the base of Jezero Crater bolsters hopes that traces could be found in the crater.

In new research published in the journal Scientists progress, a team led by UCLA and the University of Oslo shows that at some point the crater filled with water, depositing layers of sediment on the crater floor. The lake then shrank and the sediments carried by the river which fed it formed an enormous delta. As the lake dissipated, the crater’s sediments eroded, forming the geological features visible on the surface today.

Periods of deposition and erosion occurred over eons of environmental change, the radar says, confirming that inferences about the geologic history of Jezero Crater based on images of Mars obtained from space are accurate.

“From orbit we can see a bunch of different deposits, but we can’t say for sure whether what we see is their original state or whether we see the conclusion of a long geological history,” said David Paige. professor of earth, planetary and space sciences at UCLA and first author of the paper. “To understand how these things formed, we need to see beneath the surface.”

The rover, which is about the size of a car and carries seven scientific instruments, has been exploring the 30-mile-wide crater, studying its geology and atmosphere, and collecting samples since 2021. The soil and rock samples from Perseverance will be brought back to Earth. by a future expedition and studied for evidence of past life.

Between May and December 2022, Perseverance passed from the crater floor into the delta, a vast expanse of 3 billion-year-old sediments that, from orbit, resembles river deltas on Earth.

As the rover headed toward the delta, the Perseverance Radar Imager for Mars Subsurface Experiment, or RIMFAX, fired radar waves downward at 10-centimeter intervals and measured the pulses reflected from depths about 20 meters below the surface. Using radar, scientists can see down to the base of the sediments to reveal the upper surface of the buried crater floor.

Years of research with ground-penetrating radar and testing of RIMFAX on Earth have taught scientists how to read the structure and composition of underground layers from their radar reflections. The resulting underground image shows rock layers that can be interpreted as a highway cutting.

“Some geologists say radar’s ability to see beneath the surface is a bit like cheating,” said Paige, who is RIMFAX’s deputy principal investigator.

RIMFAX imagery revealed two distinct periods of sediment deposition sandwiched between two periods of erosion. UCLA and the University of Oslo report that the crater floor beneath the delta is not 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 sediments deposited in Earth’s lakes. The existence of lake sediments had been suspected in previous studies, but was confirmed by this research.

A second period of deposition occurred when fluctuations in lake level allowed the river to deposit a large delta that once extended far into the lake, but which has now eroded closer to the mouth of River.

“The changes we see preserved in the rock record are due to large-scale changes in the Martian environment,” Paige said. “It’s cool that we can see so much evidence of change in such a small geographic area, allowing us to expand our findings to the scale of the entire crater.”