Rocks on floor of Jezero Crater, Mars, show signs of sustained interactions with water

The Perseverance Rover takes a selfie above the rock from which it took two core samples on Mars. Credit: NASA/JPL-Caltech/MSSS.
The Perseverance rover has been exploring Jezero crater, Mars's oldest lake, since it landed there in February. The Mars 2020 mission and Perseverance are searching for signs of ancient Mars life and preparing samples for analysis on Earth.

Katie Stack Morgan, Mars 2020 Deputy Scientist, is a researcher scientist at NASA's Jet Propulsion Laboratory. She will provide an update on early results from the Mars 2020 rover mission at the Geological Society of America’s Connects 2021 annual meeting, Portland, Oregon.

The scientific team used Perseverance's high tech suite of instruments onboard to analyze the rocks in the crater floor. They have been interpreting them as igneous rocks and a possible volcanic lava flow.

"The possibility that this could have been a volcanic rock appealed to us from a sample-return perspective, as igneous rocks can be used to get accurate age dates. Jezero was an ancient crater lake site on Mars that had both amazing sedimentary deposits and volcanic deposits. This could have helped us to construct the geologic timescale of Mars," stated Stack Morgan.

Jezero crater was likely to have been habitable around 3.83.6 billion year ago. However, it will be possible to date the rocks in Earth's laboratories and get the first definitive insight into when the lake system and rivers were active.

Perseverance's abrasion instrument, which scratches the rock's top to reveal its textures, revealed that the crater floor is composed of coarser-grained and igneous minerals. There are also many salts within the rocks. The rocks have been subject to significant amounts of water, which could explain why they were weathered and altered.

Perseverance used its on-board tools for analyzing the characteristics of the crater's floor. The next step was to take a rock sample with its drill feature. Perseverance's first attempt at drilling failed and the core sample tube was returned empty.

"We spent several days looking at the rover, thinking the core might have fallen from the bit. We then looked down at the drill hole and thought it might not have made it out. All of these searches were unsuccessful. Stack Morgan said that we ultimately concluded that the core had been pulverized during drilling.

It is likely that the rock was so altered and weakened by water interactions that the Perseverance drill vibrations and power pulverized it.

Perseverance then found another rock that was more resistant to weathering and was able to collect two core samples. This was the first sample in its collection. Perseverance's collection of samples will be part a multi-spacecraft handoff that is still in development and will hopefully be returned to Earth by the 2030s. Scientists on Earth will analyze and date the rocks in order to determine if they contain any evidence of ancient Martian life.

The rocks on the crater floor weren't originally intended to be the primary astrobiology target for the mission. But Mars surprises us every time we look up at it. Stack Morgan said that even these rocks could have been habitable for ancient martian microbes, and they are happy to report this.

Perseverance boost case provides additional information on Mars rocks.

More information: Session 14, T117. Perseverance at Jezero CraterCharacterizing a Ancient Crater Lake Basin in MarsPaper 14-1. Early results from Mars 2020 Perseverance Rover in Jezero Crater. Session 14 is T117. Perseverance at Jezero CraterCharacterizing an Ancient Crater Lake Basin on MarsPaper 14-1: Early results from the Mars 2020 Perseverance rover in Jezero Crater, Mars Sunday, 10 Oct., 88:15 a.m., Oregon Convention Center, Portland Ballroom 256 (Hybrid Room)