Supersaline water could have erased some evidence of life on Mars

Rocks on Mars retain a record of the planet’s ancient past, but a startling discovery by NASA’s Curiosity rover shows that some patches of Martian rock have had their history completely erased.

The main objective of the NASA Curiosity mission is to assess the previous potential for habitability on Mars, while the new arrival Objectives of the Perseverance mission to find real remains or signs of previous life. To this end, Curiosity studied the sedimentary rocks of Gale Crater, which are filled with clay minerals. Clay is an important marker of livability because it suggests the past presence of liquid water, a key ingredient for life.

Using his instrument of chemistry and mineralogy, also known as Path, the six-wheeled rover analyzed drill samples of sedimentary layers along the lower parts of Mount Sharp. In 2019, a chance path from Vera Rubin Ridge to Glen Torridon allowed Curiosity to examine a layer of mudstone that formed in a Martian lake about 3.5 billion years ago.

The rover took samples from two areas within 1310 feet (400 meters) of each other. Research published today in Science described unexpected differences in these two areas, as one plot contained only half of the expected amount of clay minerals. Instead, these ancient mud stones were filled with iron oxides, which, interestingly enough, is what gives Mars its iconic red hue.

The mudstone in both plots dates from the same time and place, so they are expected to contain similar amounts of clay minerals. The startling observation forced the researchers, led by Tom Bristow of NASA’s Ames Research Center, to come up with an explanation for the missing clay. Indeed, ancient rocks are known to be custodians of history, but as new research shows, natural geological processes can undo this record.

To explain what happened, the team came up with a scenario in which water seeped into the clay from a sulphate deposit directly above it. The super salty brines seeped through the grains of sand at the bottom of the old lake and in doing so changed the mineral-rich layers underneath forever.

“We thought that once these layers of clay minerals formed at the bottom of the lake in Gale Crater, they stayed that way, preserving when they formed over billions of years,” Bristow explained in a NASA statement. “But later, brines destroyed these clay minerals in places, essentially resetting the rock record.”

In an email, Bristow said the new research adds to the emerging image of ancient Martian habitability.

“This confirms previous evidence which showed that fluids continued to move through the rocks of Gale Crater long after they were deposited,” he explained. “It also shows that there were geochemical gradients – some parts of the rocks were affected more than others and the chemistry of the fluids changed,” Bristow said, adding that biological organisms “can use geochemical gradients to capture energy.”

This process was not uniform at the bottom of the old lake, as it happened after the lake lost its liquid water, according to the research. Groundwater from Gale Crater continued to flow – and also carry and dissolve chemicals – below the surface. As a result, some underground mudstone pockets were exposed to different conditions. These pockets exposed to salt water underwent a process called “diagenesis,” in which changing mineralogy wiped out the geological records, and possibly biological records.

Interestingly, if not ironically, diagenesis could create microbe-friendly environments even though he erased potential proof of life, according to John Grotzinger, study co-author and professor of geology at Caltech.

“These are great places to look for evidence of ancient life and assess livability,” Grotzinger said in the release. “Even though diagenesis can erase the signs of life in the original lake, it creates the chemical gradients necessary to support life underground, so we’re really excited to have discovered this.”

I like this paper for several reasons. First, it improves our understanding of geological processes on the Red Planet and its unanticipated complexities. Second, it’s a reminder that Curiosity is still doing important work on Mars, even when new. years after he started riding and Perseverance began to steal the show.

This study can now inform the Perseverance team as it assesses investigative targets and selects rock samples that could potentially be brought to bear. Earth for further analysis. Interestingly, the two rovers are now working as a team (even though they’re 2,300 miles apart) and in doing so they can influence each other.

After: NASA’s other Martian rover returns a selfie to remind us it still exists.