Scientists have just found evidence suggesting past life on Mars. Although not a particularly novel idea, acting NASA Administrator Sean Duffy is calling this finding “the closest we have ever come to discovering life on Mars.”
This discovery came from NASA’s Perseverance rover exploring rocks by the Neretva Vallis, a dried river body formed by water flowing into the Jezero Crater. Previously, Perseverance had confirmed suspicions that the Jezero Crater was once a lake. The sedimentary rocks in that area contain clay and silt, materials known by biologists as good preservers of signs of past microbial life on Earth.
Perseverance examined a rock from this area of around 3.2 by 2.0 feet. The rock contains colorful spots indicative of certain chemical compounds that may have arisen from past microbial life. Specifically, microbes may have utilized the rock’s organic carbon, sulfur, and phosphorus for energy and left these colorful spots behind. According to a study published in the journal Nature on Sept. 10, these spots contain likely signatures of specific elements known on Earth for being produced by microbes or existing near decaying organic matter.
Although these colorful spots may have been produced by ancient Martian life, scientists were careful to consider other possible explanations. The minerals found in the rock could have otherwise been produced under intense heat, though these reactions appear to have occurred at lower temperatures. The minerals could also have been formed by acidic conditions, though evidence for acidic conditions is nonexistent. It is also possible, but unconfirmed, that the required reactions may have been possible at more moderate temperatures even without life.
Ultimately, alternate explanations for the signs of life are certainly possible given the right conditions, hence the term “potential biosignatures” to refer to these chemical spots. The study authors note that studying the rocks with instruments only available on Earth would likely answer whether these spots have a biological origin. Returning Martian rocks is the eventual goal of the Mars 2020 mission, though Perseverance itself will not return to Earth.
This is only the latest step in a long and ongoing search for evidence of past life on Mars. Part of this search has been the hunt for what enables life: water. Nowadays, it is known that Mars once had flowing water on its surface, and continues to have frozen polar ice caps sitting above the surface with more frozen water lying beneath its surface.
Aside from supposed canals on Mars, astronomers over a century ago saw features that were later discovered to be optical illusions, and various other speculations. NASA rigorously confirmed water once flowed on the surface of Mars in 2004, once its Spirit and Opportunity rovers landed that year. Opportunity found rock patterns within a crater indicative of past flowing water, and nearby chemicals suggesting the area was likely once the shore of a salty Martian sea. Then, in 2008, NASA’s newly landed Phoenix spacecraft searched the arctic plains of Mars and quickly found evidence of ice remaining under Mars’ surface.
Many other breakthroughs in exploring whether life lived on Mars have concerned the question of whether life can exist on Mars. For instance, in 2013, NASA’s Curiosity rover examined some flat bedrock that led scientists to conclude that ancient Mars was habitable for microbial life.
The rocks Perseverance recently discovered are not the first Martian rocks that have been noted for potentially indicating past life. One sample found in 1984 clearly shows that liquid water was present upon the rock’s formation and contains a mineral that on Earth correlates with the presence of microbes. This rock was a meteorite found in Antarctica that had landed on Earth approximately 13,000 years ago, and it is not the only Martian meteorite that has found its way to Earth. The trouble with meteorites is that, during their time on Earth, they undergo changes that may obscure features which could otherwise be hints at past Martian life.
Hopes of life on Mars have also undergone ups and downs. For instance, stronger claims once surrounded the Antarctic meteorite from 1984. Another material of interest found in the meteorite was argued to support past life on Mars, but this material is overall quite common, not only in Martian meteorites but also in asteroids and comets. Additionally, elongated potential fossils of ancient microbes were eventually widely concluded not to have biological origins. Other doubts of supposed possible indications of past Martian life are commonplace. This includes the argument that the organic compounds found on Mars that we expect to derive from life may have non-biological origins.
Whether or not life once existed on Mars is an open question — there is a nonzero chance microbial life continues to exist underground within Mars. Evidence surfaces, asterisks on that evidence’s significance emerge, and the cycle repeats. Perhaps this discovery or future discoveries will finally break the cycle and answer the question of whether life existed on Mars.