Scientists have discovered that rock samples from the Jezero Crater on Mars contain minerals that generally form in water. While the presence of organic material remains unclear, these rocks may represent the best opportunity for scientists to uncover evidence of ancient life on Mars.
A recent study published in the journal AGU Advances by researchers from MIT and NASA reveals that seven samples of rocks taken from the “fan front” of Jezero Crater exhibit minerals that typically form in aquatic environments. These findings indicate that the rocks were either deposited by water or formed while water was present.
The seven samples were collected by NASA’s Perseverance rover in 2022 while exploring the crater’s western slope, where it was suggested that some rocks might have originated from what was once a large ancient lake. The Perseverance science team, alongside MIT researchers, has analyzed the rover’s images and chemical data, confirming the presence of water in these rocks and indicating that the crater was likely once a habitable, watery environment.
It remains uncertain whether the crater itself hosted any form of life. The team was unable to confirm the existence of organic material—essentially, the building blocks of life—based on the rover’s readings. However, the mineral composition of the rocks leads scientists to believe that they hold the most promise for uncovering signs of ancient Martian life once they are returned to Earth for further study.
“These rocks affirm the previous existence of conditions suitable for life on Mars, at least temporarily,” explained Tanja Bosak, the study’s lead author and a professor of geobiology in MIT’s Department of Earth, Atmospheric, and Planetary Sciences (EAPS). “Our findings indicate significant water activity, but the duration of this activity is still a mystery. Nevertheless, it was evidently long enough to create large sediment deposits.”
Remarkably, some of the samples may date back over 3.5 billion years, potentially predating the earliest evidence of life on Earth.
“These are the oldest water-deposited rocks we’ve ever encountered, either directly or via the rover,” noted Benjamin Weiss, co-author and the Robert R. Shrock Professor of Earth and Planetary Sciences at MIT. “This is thrilling because they represent our best chance for uncovering fossils and life markers.”
The team of MIT co-authors also includes postdoctoral researcher Eva Scheller and research scientist Elias Mansbach, as well as other members of the Perseverance science team.
Collection at the Fan Front
The samples were gathered during the rover’s Fan Front Campaign in 2022, an exploration phase in which Perseverance moved along the western slope of Jezero Crater, an area characterized by layered, sedimentary rocks that resemble a fan. Scientists suspect this “fan front” may have formed as an ancient delta where sediment carried by a river accumulated in what is now a dry lakebed. If life ever existed on Mars, scientists believe its remnants could be preserved within these sediment layers.
Ultimately, Perseverance collected seven samples from various spots along the fan front, extracting them by drilling into the Martian bedrock to retrieve pencil-sized cores, which were sealed in tubes for future return to Earth for analysis.
Before extracting the cores, the rover took images of the surrounding sediments at each site. The science team analyzed these imaging data to determine the average grain size and mineral makeup of the sediments. Results indicated that all seven samples likely show evidence of water, suggesting they were deposited by it.
Specifically, Bosak and her team found minerals within the sediments that are known to precipitate from water.
“We discovered numerous minerals such as carbonates, which are essential components in Earth’s reefs,” said Bosak. “These materials are ideal for preserving microbial life fossils.”
Intriguingly, the researchers also found sulfate minerals in some samples collected near the bottom of the fan front. Sulfates form in highly saline waters, providing additional evidence that water was once present in the crater, though Bosak notes that very salty water is not necessarily conducive to life. If the entire crater was filled with saline water, it would likely hinder the survival of any life. However, if only the lake’s bottom was very salty, this could work in favor of preserving signs of life that may have existed in less salty layers above it.
“Regardless of the salinity levels, organic matter would be well-preserved, akin to pickling,” Bosak mentioned. “If any organism fell into saline layers, it would have a better chance of being preserved.”
Uncertain Organic Evidence
However, the team stresses that organic matter has not yet been reliably detected by the rover’s instruments. While organic material can indicate the presence of life, it can also arise from certain geological processes unrelated to living organisms. The previous Curiosity rover found organic molecules dispersed throughout Gale Crater, which scientists believe may have originated from asteroid impacts.
In an earlier exploration, Perseverance detected what seemed to be organic molecules scattered along Jezero Crater’s floor. These observations were made using the rover’s SHERLOC (Scanning Habitable Environments with Raman and Luminescence for Organics and Chemicals) instrument, which utilizes ultraviolet light to examine the Martian surface. If organics are present, they can fluoresce like materials under a blacklight. The wavelengths of this fluorescence can essentially fingerprint the types of organic molecules found.
During its previous exploration of the crater floor, SHERLOC identified possible organic molecules across various locations, and subsequently at some sites along the fan front. However, an in-depth analysis led by MIT’s Eva Scheller revealed that while the observed wavelengths might indicate organic materials, they could equally represent signatures of inorganic substances.
“It turns out that cerium metals found in minerals produce very similar signals to those of organic matter,” Scheller explained. “Upon examination, the potential organic signals were closely linked to phosphate minerals, which consistently contain cerium.”
Her research indicates that the rover’s findings cannot definitively confirm the presence of organic matter.
“This isn’t disappointing news,” Bosak clarified. “It implies that organic matter isn’t abundant, but it’s still possible it’s present below the rover’s detection threshold.”
When the gathered samples finally make their way back to Earth, Bosak is confident that laboratory instruments will possess the sensitivity needed to detect any organic materials present.
“On Earth, with our microscopes that can achieve nanometer-scale resolution and various sophisticated instruments, we can thoroughly search for signs of life,” she said.
This research was partially funded by NASA.
