In a groundbreaking development, two minerals closely associated with microbial metabolism have been discovered in a recent drill sample collected by NASA's Perseverance rover. This remarkable find has ignited a wave of excitement within the scientific community, prompting NASA Acting Administrator Sean Duffy to emphasize the significance of these minerals, stating, “the closest we have ever come to discovering life on Mars.” The two minerals, vivianite and greigite, are at the center of this thrilling discovery.
According to the Mineralogical Society of America, greigite is a mineral that forms through the activity of magnetotactic bacteria and sulfate-reducing bacteria found in lake soils or hydrothermal vents. This mineral is notable because it is among several materials that scientists believe could have acted as catalysts for the origin of life on Earth. Specifically, a certain iron-based unit in greigite is present in a protein crucial for driving the acetyl-COA pathway, a fundamental metabolic process that underpins cellular respiration.
Vivianite, on the other hand, is a hydrated iron phosphate mineral commonly found in fossils, as well as in the shells of bivalves and gastropods. It is also associated with human burial sites, resulting from the chemical reactions that occur as decomposing bodies interact with iron enclosures. Interestingly, while the prefix "vivi" in vivianite may suggest a connection to life, it is actually named after the scientist John Henry Vivian.
Both vivianite and greigite were identified in a core sample taken from Neretva Vallis, an ancient river channel approximately a quarter mile wide that once flowed into a lake situated at the bottom of Jezero Crater. This crater has been the focal point of Perseverance's search for evidence of microbial life for over five years. Duffy remarked, “This finding by Perseverance is the closest we have ever come to discovering life on Mars," highlighting the importance of this potential biosignature in advancing our understanding of the Red Planet.
NASA's commitment to conducting what it terms "Gold Standard Science" remains unwavering as the agency continues its mission to send humans to Mars. The recent budget allocation reflects this commitment, linking funding directly to human exploration efforts while canceling a billion-dollar sample return mission that would have gathered additional cores from Neretva Vallis. Instead, NASA plans to have astronauts collect these samples directly, simplifying the process of studying Martian geology.
Reports from Earth.com reveal that the sample sediments displayed a ring of vivianite interspersed with small “leopard spot” cores enriched in greigite. This pattern aligns with sequences observed in biologically mediated vivianite influenced by extracellular electron transfer, a key metabolic pathway known to occur in biologically active sediments on Earth. While these findings do not conclusively prove that the Neretva Vallis samples originated from microbial activity, they represent the closest approach yet to detecting signs of life on Mars.
This significant discovery has the potential to extend the timeframe during which Mars was possibly habitable, providing important reference dates for future studies. With such a strong biosignature identified within just six years of exploration, there is optimism that further evidence of mineral cycling related to life may be uncovered in upcoming samples or missions.
The critical question moving forward is whether scientists can demonstrate that greigite and vivianite require biological processes for their formation, as opposed to occurring through abiotic means. Additionally, researchers must investigate whether there are specific signatures that biotic versions of these minerals possess, setting them apart from their abiotic counterparts. The answers to these questions could prove to be among the most significant milestones in the ongoing quest to determine whether Mars was ever inhabited by microbes.
