News release

From: Springer Nature

Nickel-rich rocks reveal ancient Martian chemistry

The discovery of nickel-rich Martian rocks in Neretva Vallis — an ancient river channel that once carried water into a lake in Jezero crater — by NASA’s Perseverance rover is described in a paper published in Nature Communications. The findings may provide further insight into chemical reactions that occurred on early Mars.

Henry Manelski and colleagues used a laser, infrared spectrometers, and an X-ray spectrometer on the Perseverance rover to examine 126 sedimentary rocks and 8 rock surfaces in Neretva Vallis that are believed to be over 3 billion years old. They detected nickel in 32 rocks in concentrations up to 1.1% of their weight, which the authors note is the highest abundance observed in Martian bedrock to date. They observed that nickel tended to co-occur with iron sulfide compounds and with sulfate minerals produced from the breakdown of these rocks, such as jarosite and akaganeite.

The authors identify similarities between the chemical composition and shape of the nickel-rich iron sulfide arrangements in Neretva Vallis and those of pyrite — an iron sulfide mineral — in sedimentary rocks on Earth. Previous studies have suggested that iron sulfides in sedimentary rocks on Earth are primarily formed from microbial anaerobic respiration using sulfates in the presence of iron-containing minerals. Previous research has also detected iron sulfides in Neretva Vallis in the presence of organic carbon compounds and it has been proposed that these compounds could have been formed by living organisms. However, the authors note that they could also result from reactions that do not involve living organisms and emphasise that their current research does not provide evidence of such organisms.

Nickel is an essential component of enzymes in many ancient archaea and bacterial species and is required for some chemical pathways used in energy generation, carbon fixation, and organic matter decomposition. The authors suggest that the presence of nickel-rich rocks indicates that, if living organisms had been present on early Mars, nickel may have been available in a form that they could have used. They speculate that the nickel may have originated from the breakdown of igneous rocks or from a nickel-rich meteorite.

The authors conclude that further research is needed to determine the source of nickel in Neretva Vallis and to investigate possible connections between it and organic matter in this location.