Between July and November 2022, NASA’s Perseverance rover gathered seven sediment samples from an ancient alluvial fan located within Jezero crater. Initial onboard tests provided some insights regarding their composition, but comprehensive examinations on Earth are necessary to uncover how and when water existed on Mars and whether it may have supported life. Although geophysicists aimed to return these samples by 2033, it is likely that NASA’s sample return mission may face delays past that timeline.
In nearly five months during 2022, NASA’s Perseverance rover collected rock samples from Mars that could change our understanding of water history on the Red Planet and possibly indicate evidence of ancient life.
However, the valuable information from these samples cannot be fully explored without further detailed studies on Earth, necessitating a mission to retrieve the samples. Scientists remain hopeful to have these samples returned by 2033, but it may take longer due to potential delays in NASA’s sample return mission.
“These samples are the main objective of our mission,” stated David Shuster, a co-author and earth and planetary science professor at the University of California, Berkeley, also part of NASA’s sample collection team. “This is exactly what we aimed to achieve, and we have succeeded. These samples are why we came here.”
The significance of these samples, taken from river deposits in a dried lake that once filled Jezero crater, is elaborated in a study slated for publication on August 14 in AGU Advances, a journal associated with the American Geophysical Union.
“These represent the first and only sedimentary rocks ever examined and collected from a planet other than Earth,” Shuster remarked. “Sedimentary rocks are crucial because they are formed from materials carried by water, deposited into standing water, and chemically altered by interactions with liquid water on Mars at some point in its history. Our mission’s focus on studying this type of rock is precisely why these samples are so critical to our goals.”
Shuster is co-authoring the paper with Tanja Bosak, a geobiologist from the Massachusetts Institute of Technology (MIT) in Cambridge.
“These rock cores might be the oldest materials collected from environments that could have supported life,” Bosak said. “Upon their return to Earth, they can reveal much about when, why, and for how long liquid water was present on Mars, including whether organic, prebiotic, or even biological developments occurred there.”
Significantly, some of the samples include very fine-grained sediments, which are the most promising for preserving traces of any past microbial life on Mars, if such life ever existed.
“The presence of liquid water is vital because it’s essential for biological processes, as we currently understand them,” stated Shuster, a geochemist. “On Earth, fine-grained sedimentary rocks are the most likely to retain evidence of former biological activity, including organic molecules. Hence, these samples are of great importance.”
On July 25, NASA announced that Perseverance gathered additional rock samples from an outcrop called Cheyava Falls, which may also show signs of past life on Mars. The rover’s instruments found indications of organic molecules, and peculiar “leopard spot” features within the rocks resemble those on Earth associated with fossilized microbial life.
Ken Farley, Perseverance project scientist at Caltech, commented, “Scientifically, Perseverance has completed its data-gathering phase. To completely understand what transpired in the Martian river valley at Jezero crater billions of years ago, we need to return the Cheyava Falls sample to Earth for analysis using advanced laboratory equipment.”
Sediments hold the answers
Shuster highlighted that Jezero and the sediment fan formed by the river likely emerged around 3.5 billion years ago. That substantial water is now missing, absorbed underground or expelled into space. During that ancient period, Earth was teeming with microbial life.
“Life was thriving on Earth at that time, 3.5 billion years ago,” he explained. “The fundamental question remains: Did life also exist on Mars during that period?”
“Historically, on Earth, if you provide me with a scenario where a river flowed into a crater, bringing materials to a standing body of water, life would have made its presence known and left marks in some form,” Shuster elaborated. “In fine-grained sediments, we would significantly enhance our chances of detecting biological evidence through laboratory investigations of those materials once back on Earth.”
Shuster and Bosak acknowledged that the rover’s organic analysis tools did not identify organic molecules in the four samples taken from the sedimentary fan. Organic molecules, a key aspect of life as we know it, are not definitive proof of life even when detected.
“We did not clearly identify organic compounds in these crucial samples,” Shuster noted. “However, the absence of detected organic compounds does not exclude the possibility that they are present; it simply indicates they were not found at detectable levels using the rover’s instrumentation.”
To date, the Perseverance mission has collected a total of 25 samples, including duplicates and atmospheric samples, plus three “witness tubes” that are intended to capture potential contaminants near the rover. Eight duplicate rock samples, along with an atmospheric sample and a witness tube, have been placed in a backup cache called Three Forks on Jezero’s surface, to protect against possible issues with the rover preventing sample retrieval. The 15 remaining samples, including the one from Cheyava Falls collected on July 21, are still housed onboard the rover awaiting retrieval.
Shuster contributed to the analysis of the initial eight rock samples collected — two from each location on the crater floor. These samples were primarily igneous rocks likely formed during a meteor impact that excavated the crater, as reported in a 2023 study based on data collected by Perseverance’s instruments.
The latest paper focuses on an analysis of seven additional samples, three of which are duplicates stored on Mars, collected between July 7 and November 29, 2022, from the front of the western sediment fan in Jezero. Bosak, Shuster, and their team found that these rocks mainly consist of sandstone and mudstone, both shaped by fluvial activity.
“Perseverance found sedimentary rocks that formed under water at the front, top, and edges of the western Jezero fan. The samples include eight carbonate-bearing sandstones, a sulfate-rich mudstone, a sulfate-rich sandstone, and a sand-pebble conglomerate,” Bosak explained. “The oldest rocks come from the fan front, while the younger rocks were sourced from the fan top, influenced by water and sediment deposition in the western fan.”
While Bosak is particularly interested in potential signs of life within the fine-grained sediments, Shuster pointed out that the coarse-grained sediments hold valuable information regarding Mars’ water history. Though less likely to preserve organic or potential biological materials, they contain carbonate materials and debris carried by the now-extinct river. As such, these samples could provide insights into when Mars had flowing water, a primary focus of Shuster’s research.
“By analyzing these detrital minerals in the lab, we can make precise claims about when the sediments were deposited and the chemistry of the water at that time. What was the pH of the water during the formation and deposition of those secondary minerals? At what stage did chemical alterations occur?” he queried. “With this collection of samples, we can learn about the environmental conditions when liquid water flowed into the crater. Was the water flow consistent or intermittent?”
Finding answers to these questions will depend on laboratory analyses of returned samples, focusing on the organic, isotopic, chemical, morphological, geochronological, and paleomagnetic data they contain, the researchers emphasized.
“One of the primary objectives in planetary science is to ensure these samples are brought back,” Shuster concluded.
