Nickel in Neretva Vallis Offers New Clues to Ancient Life on Mars

The identification of plentiful nickel in a Martian area that was once saturated with water provides another indication that the red planet may previously have had conditions capable of supporting life.

In Neretva Vallis, an ancient watercourse that once fed the Jezero Crater delta, scientists have identified nickel levels in bedrock that exceed any previously recorded on Mars. Viewed alongside the wider geology of the area, the metal reveals details of the region’s chemical past and supplies another clue to the planet’s former habitability.

Nickel in Neretva Vallis bedrock

"While nickel has been detected on Mars before, this is our strongest detection to date outside of iron-nickel meteorites found on the Martian surface," planetary scientist Henry Manelski of Purdue University told ScienceAlert.

"Generally, nickel is a trace element on the surfaces of Earth and Mars because the vast majority of it migrates into the planets' cores during their formation. The substantial amount we have detected on the surface places unique constraints on how these rocks formed and were subsequently altered."

Although Mars is not wholly lacking in nickel, the element is generally encountered in meteorite fragments dispersed over its surface.

During 2024, NASA’s Perseverance rover travelled through the long-parched Neretva Vallis and encountered several unusual rocks. These included a notably light-coloured exposed bedrock area, which researchers called Bright Angel.

Bright Angel contained several intriguing characteristics commonly linked with microbial activity on Earth. They included iron-sulphide minerals resembling pyrite, which is frequently present in microbe-rich settings, as well as organic compounds.

As part of its mission, Perseverance gathered compositional information from numerous rocks throughout Neretva Vallis. Manelski and his team examined those data for evidence of the processes that created the rocks. That work revealed an unusually powerful nickel signal.

What the nickel concentrations could reveal about ancient Mars

Among 126 sedimentary rocks and eight rock surfaces examined by Perseverance, the team identified 32 containing nickel at concentrations of up to 1.1 percent by weight. However, the accompanying material within those rocks is what begins to clarify the wider picture.

"Nickel-rich iron-sulfide is observed on Earth in ancient sedimentary rocks. Iron sulfide weathers easily in oxygen-rich environments, so its presence in ancient terrestrial rocks is one line of evidence used to demonstrate that Earth's early atmosphere was once very oxygen-poor," Manelski explained.

"This is in stark contrast to another environment where nickel is often found on Earth: laterites, which are highly weathered ancient soils. Observing nickel in iron-sulfide suggests these rocks likely formed in a reducing (oxygen-poor) environment."

These minerals also indicate an active water-rich setting. Neretva Vallis rocks seem to have been altered by water flowing through their sediments and triggering chemical reactions over time.

The researchers suggest nickel could have arrived within a meteorite before being dissolved and spread elsewhere by water. Crucially, nickel is an essential element for many Earth organisms, microbes among them.

The nickel concentrations observed by the researchers indicate that the element may have been accessible to living organisms, although they do not suggest that life was present to make use of it.

Rocks studied by Perseverance also contained organic compounds: carbon-bearing molecules. Carbon, the element underpinning all life on Earth, can certainly be produced through many non-biological processes. Yet, like water, it is indispensable to life as we know it.

Organic carbon and potentially habitable conditions at Jezero Crater

"As we search for evidence of life on ancient Mars, it is useful to draw parallels to life on ancient Earth. Life around 3.5 to 4 billion years ago – the approximate age of Jezero Crater – was dominated by anaerobic microbes," Manelski said.

"Our detection of high nickel abundances directly adjacent to our first discovery of organic carbon and macroscopic zones of reduced sulfur suggests nickel was bioavailable. This further supports the idea that the ingredients for life were present on ancient Mars."

The results additionally prompt questions over the timing of such conditions. Since Neretva Vallis rocks could be younger than rocks elsewhere in Jezero Crater, potentially habitable Martian environments may not have been confined to the planet’s earliest period.

"Our finding of a seemingly habitable environment for ancient microbial life implies that our search for biosignatures in ever older rocks could be somewhat misplaced," Manelski said, "and we should remain open-minded to exciting discoveries wherever our rovers explore."

The research has been published in Nature Communications.