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The Perseverance rover has confirmed that sediments from a lake at the base of Jezero Crater may contain traces of life on Mars.
New research published in the Journal Science AdvancesThe team, led by UCLA and The University of Oslo, shows that the crater at some point filled with water. Layers of sediments were deposited on the floor of the crater. The lake shrank, and sediments carried along by the river that fed into it formed a massive delta. As the lake dwindled over time, sediments in the crater became eroded. This is what we see today.
Radar images confirm that the inferences about Jezero’s geologic past based on Mars images taken from space were accurate.
“From orbit, it’s possible to see a lot of different deposits. However, we cannot tell for certain if they are in their original form or if the geological story is coming to an end,” said David Paige. Paige is a UCLA Professor of Earth, Planetary and Space Sciences and the first-author of the paper. To tell how these things form, we need to look below the ground.
The rover has been exploring this 30-mile wide crater for the past 2021. It has studied its geology and atmospheric conditions and collected samples. Perseverance’s rock and soil samples will be brought to Earth by future expeditions and studied for evidences of past life.
Perseverance, between May and Dec 2022, will have driven from the crater’s floor onto the delta. This vast expanse of sediments 3 billion years old, which from orbit resembles river deltas on Earth, is the result of Perseverance’s drive.
As the rover drove into the delta, the Perseverance’s RIMFAX instrument fired downward radar waves at 10-centimeter spacing and measured pulses reflecting from depths up to 20 meters beneath the surface. Scientists can use radar to see the top surface of a buried crater’s floor.
Scientists have learned how to read subsurface layers’ structure and composition from radar reflections after years of research using ground-penetrating Radar and testing RIMFAX in Earth. The subsurface image is interpreted as a highway road cut.
Paige, RIMFAX deputy principal investigator, said: “Some geologists claim that radar’s ability to see below the surface is similar to cheating.”
RIMFAX imaging revealed that there were two distinct periods of deposition of sediment sandwiched between periods of erosion. UCLA and the University of Oslo reported that the crater bottom below the delta was not uniformly flat. This suggests that erosion took place before the lake sediments were deposited. Radar images show that sediments are horizontal and regular – just like sediments in lakes on Earth. Previous studies had suggested the existence of sediments from lakes, but this research has confirmed it.
A second period of eroding occurred when fluctuations in lake levels allowed the river to deposit an extensive delta that once extended out into the Lake, but now has eroded closer to river’s mouth.
Paige said that the changes preserved in the rock records are a result of large-scale changes to the Martian environment. “It is cool that we are able to see so much evidence for change in such a limited geographic area. This allows us to extend our discoveries to the scale the entire crater.”