"These samples are the reason why our mission was flown," stated David Shuster, a professor of earth and planetary science at the University of California, Berkeley, and a member of NASA's science team for sample collection. "This is exactly what everyone was hoping to accomplish. And we've accomplished it. These are what we went looking for."
The rocks, extracted from ancient river deposits in Jezero Crater, are highlighted in a study to be published on Aug. 14 in AGU Advances, a journal of the American Geophysical Union.
"These are the first and only sedimentary rocks that have been studied and collected from a planet other than Earth," said Shuster. "Sedimentary rocks are important because they were transported by water, deposited into a standing body of water, and subsequently modified by chemistry that involved liquid water on the surface of Mars at some point in the past. The whole reason that we came to Jezero was to study this sort of rock type. These are absolutely fantastic samples for the overarching objectives of the mission."
Shuster co-authored the paper with Tanja Bosak, a geobiologist at the Massachusetts Institute of Technology (MIT).
"These rock cores are likely the oldest materials sampled from any known environment that may have supported life," said Bosak. "When we bring them back to Earth, they can tell us so much about when, why, and for how long Mars contained liquid water, and whether some organic, prebiotic, and potentially even biological evolution may have taken place on that planet."
Some of the samples contain fine-grained sediments, which are particularly promising for preserving potential evidence of past microbial life on Mars - if life ever existed there.
"Liquid water is a key element in all of this because it is the key ingredient for biological activity, as far as we understand it," Shuster explained. "Fine-grained sedimentary rocks on Earth are those that are most likely to preserve signatures of past biological activity, including organic molecules. That's why these samples are so important."
NASA recently announced that Perseverance had collected new rock samples from an area called Cheyava Falls, which might also hold signs of past life. The rover's instruments detected organic molecules and other features that could be linked to fossilized microbial life.
Ken Farley, Perseverance project scientist at Caltech, commented, "Scientifically, Perseverance has nothing more to give. To fully understand what really happened in that Martian river valley at Jezero crater billions of years ago, we'd want to bring the Cheyava Falls sample back to Earth, so it can be studied with the powerful instruments available in laboratories."
Shuster emphasized the importance of the sediments collected in Jezero, which formed approximately 3.5 billion years ago. The water that once flowed there has long since disappeared, either trapped underground or lost to space. At that time, life in the form of microbes was already thriving on Earth.
"Life was doing its thing on Earth at that point in time, 3.5 billion years ago," he noted. "The basic question is: Was life also doing its thing on Mars at that point in time?"
Shuster added, "Anywhere on Earth over the last 3.5 billion years, if you give me the scenario of a river flowing into a crater transporting materials to a standing body of water, biology would have taken hold there and left its mark, in one way or another. And in the fine-grained sediment, specifically, we would have a very good chance of recording that biology in the laboratory observations that we can make on that material on Earth."
Despite not detecting organic molecules in the key samples with the rover's instruments, Shuster stressed that this does not rule out their presence. "We did not clearly observe organic compounds in these key samples," he said. "But just because that instrument did not detect organic compounds does not mean that they are not in these samples. It just means they weren't at a concentration detectable by the rover instrumentation in those particular rocks."
Perseverance has so far collected 25 samples, including duplicates, atmospheric samples, and "witness tubes" that monitor possible contamination. Eight of these samples were cached on Mars as a backup in case the rover encounters issues. The remaining 15 samples, including one from Cheyava Falls, are still aboard the rover awaiting retrieval.
Shuster's earlier analysis of the first eight rock samples - mainly igneous rocks - was published in 2023. The new paper examines seven more samples, collected between July and November 2022, which include sandstone and mudstone created by fluvial processes.
"Perseverance encountered aqueously deposited sedimentary rocks at the front, top and margin of the western Jezero fan and collected a sample suite composed of eight carbonate-bearing sandstones, a sulfate-rich mudstone, a sulfate-rich sandstone, [and] a sand-pebble conglomerate," Bosak explained. The rocks from the fan's front are the oldest, while those from the top are the youngest from this period of aqueous activity.
While the fine-grained sediments are of particular interest for their biosignature potential, the coarser sediments also offer critical insights into Mars' watery past. These sediments, washed downstream and now preserved in the rocks, could reveal the timing and chemistry of water flow on the planet.
"With lab analysis of those detrital minerals, we could make quantitative statements about when the sediments were deposited and the chemistry of that water. What was the pH (acidity) of that water when those secondary phases precipitated? At what point in time was that chemical alteration taking place?" Shuster said. "We have this combination of samples now in the sample suite that are going to enable us to understand the environmental conditions when the liquid water was flowing into the crater. When was that liquid water flowing into the crater? Was it intermittent?"
The analysis of these samples, once returned to Earth, will be crucial to understanding Mars' environmental history and its potential for life.
"One of the most important planetary science objectives is to bring these samples back," Shuster concluded.
Research Report:Astrobiological potential of rocks acquired by the Perseverance rover at a sedimentary fan front in Jezero crater, Mars
Related Links
University of California - Berkeley
Mars News and Information at MarsDaily.com
Lunar Dreams and more
| Subscribe Free To Our Daily Newsletters |
| Subscribe Free To Our Daily Newsletters |
