Perseverance finds surprising evidence of water activity on ancient Mars

NASA’s Perseverance rover has uncovered unexpected evidence of repeated water activity in rocks near an ancient Martian lake, offering new clues about the Red Planet’s watery past and its potential habitability.

The discovery was made at Jezero Crater, a vast basin that once contained a lake. Perseverance reached the crater’s inner edge in September 2023 and began exploring an area known as the Margin Unit, which stretches along the ancient shoreline, BBC's Sky At Night Magazine writes.

Scientists had expected to find sedimentary rocks formed from layers of sand and silt deposited over thousands or millions of years. Such rocks are considered promising targets in the search for evidence of ancient microbial life because they can preserve traces of past biological activity.

Orbital observations had also detected carbonate minerals in the area. On Earth, carbonates commonly form in environments involving water, including lakes and oceans that can support life.

Instead, Perseverance encountered igneous rock — material formed from magma either deep beneath the surface or through volcanic activity.

Although unexpected, the rocks provided an important record of interactions between water and the Martian surface. Scientists found evidence that the rocks had interacted with water on at least three separate occasions.

The findings were made using Perseverance’s SuperCam instrument, which analyses the mineral composition of geological features and uses a laser to reveal their chemistry.

“Before we arrived at the Margin Unit, the main hypothesis – derived from orbital observations – was that the carbonate seen from orbit formed from interaction with the lake that existed in Jezero Crater,” says Candice Bedford of Purdue University, the study’s lead author.

“But now we know that this location became a sort of crossroads for aqueous systems. The Margin Unit findings are important because Jezero Crater sits inside one of the largest exposures of carbonate on Mars, so what we learn here reaches well beyond this crater.”

As Perseverance explored higher ground, it encountered coarse-grained crystalline rock bearing the characteristics of olivine, with little evidence that water had interacted with it.

Scientists believe this olivine-rich rock formed in a large body of magma deep beneath Mars before slowly cooling. Erosion later exposed the rock at the surface.

Further down, closer to the ancient lakebed, the rocks showed significant transformation. Olivine grains were fractured and surrounded by silica, while carbonate and silica minerals provided evidence of interactions with water.

These findings are significant because water interacting with olivine on Earth can release hydrogen, which can serve as an energy source for some microbes. The process can also leave carbonate and silica behind.

“Some of the Margin Unit rocks also contain silica,” says Eleni Ravanis of the University of Hawaii at Manoa and a coauthor of the study.

“Turning olivine into carbonate can leave silica behind, and we see more of that silica in rocks that sat below the water line.”

The discovery adds another piece to the puzzle of Mars’ ancient climate and habitability, as scientists continue to reconstruct how water moved across the planet billions of years ago.

“If there is one thing I have learned after 10 years working with Mars rovers, it is that Mars constantly throws surprises at you,” says Bedford.

“It is very rare that things are as we expect them to be from orbital data. I hope this work helps reshape how scientists view the history of water in Jezero Crater and across Mars. Ultimately, I hope it helps planetary scientists reconstruct the changing climate and habitability of early Mars.”

By Sabina Mammadli