The Ancient Microbial Life On Mars, The First Report Of Life Beyond Earth

Earlier this month, NASA revealed that its Perseverance rover had uncovered potential signs of ancient microscopic life on Mars, discovered last year in rocks within a long-dry river channel. While scientists stress the need for an in-depth analysis of the gathered sample in labs on Earth before reaching any conclusions, the discovery marks a significant milestone. As NASA’s science mission chief Nicky Fox put it, it is "the closest we've actually come to discovering ancient life on Mars".

In a paper, 'Redox-driven mineral and organic associations in Jezero Crater, Mars', published in the journal Nature, a group of scientists have published groundbreaking results on the sample collected by the Perseverance Rover last year, suggesting the potential of ancient microbial life.

In the abstract of the paper, the authors report that “…. a detailed geological, petrographic and geochemical survey of these rocks and show that organic-carbon-bearing mudstones in the Bright Angel formation contain submillimetre-scale nodules and millimetre-scale reaction fronts enriched in ferrous iron phosphate and sulfide minerals, likely vivianite and greigite.”

The identification of specific minerals—namely vivianite and greigite, a ferrimagnetic iron-sulfide—serves as a potential biosignature, indicating that bacterial processes likely contributed to their formation. Although the research stops short of claiming definitive evidence of fossilised life, it proposes that particular morphological features observed on the rocks could be attributed to the presence of microbial forms in the distant past.

At the end of the paper, the authors add, “In summary, our analysis leads us to conclude that the Bright Angel formation contains textures, chemical and mineral characteristics, and organic signatures that warrant consideration as ‘potential biosignatures’.

Scientists have reached this assessment by analysing data relayed by the rover, particularly its detailed chemical and mineralogical analyses. Perseverance is equipped with sophisticated instrumentation, including high-resolution cameras and spectrometers that use light to determine the precise composition of rocks and soil. To interpret this Martian data, researchers use the well-established compositional framework of Earth's geology as a reference template, comparing the mineralogy and formations found on Mars to those with known origins on our own planet.

Marked by seven benchmarks, the Confidence of Life Detection, or CoLD, scale outlines a progression in confidence that a set of observations stands as evidence of life. (Credit: NASA)

Until these samples can be analysed in terrestrial laboratories with more advanced tools, scientists rightly refrain from drawing definitive conclusions. This rigorous approach to evidence is why researchers consistently attach a caveat to such findings, emphasising that further study is essential before any firm conclusion can be reached regarding the presence or absence of ancient life on Mars.

NASA's Perseverance Rover: Journey, mission, and more

NASA's Perseverance Rover was launched on July 30, 2020, and successfully landed on Mars on February 18, 2021. Its primary mission is to explore the Jezero Crater, a site believed to have once hosted a lake, in search of signs of ancient microbial life and to assess the planet's past habitability.

NASA selected Jezero Crater as the landing site for the Perseverance rover through a rigorous, collaborative process. Mission team members and scientists from around the world spent five years evaluating more than 60 candidate locations before choosing Jezero.

The selection was driven by compelling evidence that the crater had a wet past. Scientists determined that over 3.5 billion years ago, the area was home to a lake that was fed by an ancient river delta. This environment is key to the mission's goals, as flowing water would have transported clay minerals and other materials into the crater lake.

NASA’s Perseverance Mars rover took this selfie, made up of 62 individual images, on July 23, 2024. A rock nicknamed “Cheyava Falls,” which has features that may bear on the question of whether the Red Planet was long ago home to microscopic life, is to the left of the rover near the center of the image. (Credit: NASA/JPL-Caltech/MSSS)

Crucially, such an environment could have supported microbial life. If life existed, its biosignatures might be retained in the lakebed or shoreline sediments. Therefore, the Perseverance rover is tasked with analysing the region's geological history, seeking signs of this ancient life, and collecting rock and soil samples that could contain these vital clues.

Perseverance is methodically drilling and sealing core samples from Martian rocks and regolith (broken rock and soil). These samples are being cached for potential retrieval by a future NASA-ESA (European Space Agency) mission, which would bring them back to Earth for unprecedented detailed analysis in terrestrial laboratories.

The rock with potential signs of life

The sample carrying potential signs of life on Mars was collected by the rover while exploring the fan-shaped remains of an ancient river delta within the Jezero Crater, a 45-km-wide impact basin located north of the Martian equator. Perseverance's onboard laboratory is designed to investigate the origin of geological formations and seek evidence of past water presence and organic carbon molecules. Critically, it can identify specific mineral arrangements and biosignatures that may indicate ancient microbial activity, guiding the selection of the most promising samples for eventual return.

An annotated version of the image of “Cheyava Falls” indicates the markings akin to leopard spots, which have particularly captivated scientists, and the olivine in the rock. The image was captured by the WATSON instrument on NASA’s Perseverance Mars rover on July 18. (Credit: NASA/JPL-Caltech/MSSS)

Evidence suggestive of potential microbial life was derived from a specific sample designated "Sapphire Canyon," which was obtained from a rock outcrop named "Chevya Falls" inside the crater. This precise location within the delta was targeted because such environments on Earth are known to preserve organic matter and biosignatures.

Ancient life on Mars: The significance of the discovery

The recent paper presenting evidence of possible microbial remnants on Mars represents a pathbreaking discovery. While definitive confirmation is still required, this finding brings us historically closer to a profound realisation: We may not be alone in the universe.

If future analysis confirms that these Martian microbes originated through a different biochemical mechanism, it would demonstrate that life can emerge from diverse chemical environments. Conversely, if they share a similar origin story with life on Earth, it could imply a shared pathway in the early evolution of both planets. This would present a cosmic dichotomy: one world, Earth, continued to flourish as a living blue planet, while the other, Mars, became a dead red world after its initial era of microbial life.

In either scenario, the confirmed discovery of past life on Mars would be a monumental achievement for astrobiology and planetary science, fundamentally reshaping our understanding of life's prevalence and guiding future research priorities for decades to come.

Carl Sagan, who wrote in Chapter V of his legendary ‘Cosmos’, titled 'Blues for a Red Planet', reminds us to keep our solipsistic anthropocentrism in check, while exploring for life beyond Earth:

“The surface area of Mars is exactly as large as the land area of the Earth. A thorough reconnaissance will clearly occupy us for centuries. But there will be a time when Mars is all explored; a time after robot aircraft have mapped it from aloft, a time after rovers have combed the surface, a time after samples have been returned safely to Earth, a time after human beings have walked the sands of Mars. What then? What shall we do with Mars? There are so many examples of human misuse of the Earth that even phrasing this question chills me. If there is life on Mars, I believe we should do nothing with Mars.

Mars then belongs to the Martians, even if the Martians are only microbes. The existence of an independent biology on a nearby planet is a treasure beyond assessing, and the preservation of that life must, I think, supersede any other possible use of Mars."

(CP Rajendran is an adjunct professor at the National Institute of Advanced Studies, Bengaluru)