Confirmation of ancient lake on Mars brings hope that Perseverance rover’s soil and rock samples contain signs of life

If life existed on Mars, the Perseverance rover’s examination of lake sediments at the bottom of Jezero Crater raises hopes that traces may be found within the crater.

In a new study published in the journal scientific progressA research team led by UCLA and the University of Oslo showed that at some point the crater filled with water, and a layer of sediment was deposited on the crater’s floor. The lake then shrank, and the sediment carried by the rivers that fed it formed a huge delta. As the lake disappeared over time, the sediment within the crater eroded away, forming the geological features seen on the surface today.

Radar shows that the period of deposition and erosion occurred amidst persistent environmental change, confirming that inferences about Jezero Crater’s geological history based on Mars images obtained from space are accurate. It is supported.

“While we can see various deposits from orbit, we cannot know for sure whether we are seeing the original state or the end of a long geological story. ” said David Page. He is a professor of Earth, planetary, and space sciences at the University of California, Los Angeles, and the paper’s lead author. “You have to look below the surface to see how these things formed.”

The rover, which is about the size of a car and carries seven scientific instruments, has been exploring the 30-mile-wide crater since 2021, studying its geology and atmosphere and collecting samples. Perseverance’s soil and rock samples will be returned to Earth. Future expeditions studied evidence of past life.

Perseverance reached the delta region from the crater floor between May and December 2022. The delta region is a vast area of ​​3 billion-year-old sediments that resembles Earth’s delta region when viewed from orbit.

When the spacecraft enters the delta region, Perseverance’s Radar imager for underground experiments on Mars, or RIMFAX, fired radar waves downward at 10-centimeter intervals and measured the reflected pulses at a depth of about 20 meters below the surface. Using radar, scientists can peer down to the bottom of the sediment and reveal the top surface of the buried crater floor.

Years of research with ground-penetrating radar and testing RIMFAX on Earth have taught scientists how to read the structure and composition of underground layers from radar reflections. The resulting subsurface image displays rock formations that can be interpreted like highway road cuts.

“Some geologists say that radar’s ability to see below the surface is kind of cheating,” said Page, RIMFAX’s deputy principal investigator.

RIMFAX imaging 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 sediment is regular and horizontal, similar to sediment deposited in lakes on Earth. Previous research had suspected the presence of lake sediment, but this study confirmed it.

The second period of deposition occurred when the river deposited a wide delta area due to fluctuations in lake levels. The delta region once extended deep into the lake, but has now eroded back to near the mouth of the river.

“The changes preserved in the rock record are driven by large-scale changes in the Martian environment,” Page said. “It’s great to see so much evidence of change in such a small geographic area and to be able to extend our findings to the scale of an entire crater.”