Abundant Nickel in Mars' Neretva Vallis Hints at Ancient Habitability

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

At Neretva Vallis, an ancient channel that formerly transported water into the Jezero Crater delta, scientists identified nickel levels in bedrock higher than any previously recorded on Mars. Considered alongside the area's wider geology, the metal reveals details of its chemical past and supplies another part of the puzzle surrounding the planet's former habitability.

"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."

Nickel in Neretva Vallis on Mars

Nickel is not particularly rare on Mars, although it is normally detected in meteorite fragments dispersed across its surface.

In 2024, NASA's Perseverance rover travelled through the long-dry Neretva Vallis and encountered several unusual rocks. Among them was an exceptionally pale exposed bedrock section, which scientists called Bright Angel.

Bright Angel contained intriguing characteristics often linked with microbial activity on Earth. These included iron-sulphide minerals resembling pyrite - a mineral frequently present in microbe-rich settings - as well as organic compounds.

During its mission, Perseverance gathered compositional information from numerous rocks throughout Neretva Vallis. Manelski and his team examined these data for evidence of the rocks' formation processes, and the assessment revealed an unusually powerful nickel signal.

Nickel-rich iron sulphide and ancient water

From 126 sedimentary rocks and eight rock surfaces examined by Perseverance, the team identified 32 with nickel concentrations of up to 1.1 percent by weight. What accompanied that nickel, however, 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. Water flowing through the sediments appears to have altered the rocks in Neretva Vallis, triggering chemical reactions over time.

The researchers think a meteorite may have brought the nickel to the site, after which water dissolved and redistributed it. Crucially, nickel is an essential element for many living organisms on Earth, including microbes.

The nickel quantities identified by the team indicate that the element could have been accessible to living organisms, although the researchers do not claim that life was present to make use of it.

Rocks assessed by Perseverance also contained organic compounds: carbon-containing molecules. Carbon, the element on which all Earth life is based, can of course be produced through many non-biological processes. Yet, like water, it is something life as we know it cannot exist without.

What the Mars rocks suggest about habitability

"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 also prompt questions over when such conditions were present. Neretva Vallis rocks may be younger than those in other areas of Jezero Crater, which implies that 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 findings have been published in Nature Communications.