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Researchers discover the origins of organic matter on Mars

Analysis of sediments collected by the Curiosity rover from the Gale Crater uncovered organic matter
Analysis of sediments collected by the Curiosity rover from the Gale Crater uncovered organic matter. (CREDIT: NASA/JPL-Caltech)

Mars, often characterized by its desolate, dusty terrain, seemingly stands as a stark contrast to the bustling ecosystems of Earth. Yet, beneath this barren facade, the planet's geology—marked by ancient deltas, lakebeds, and river valleys—hints at a vibrant past where water may have flowed freely.

These features have become focal points for scientists, particularly as they analyze sediments preserved within these areas to uncover clues about Mars' environmental history and the processes that have shaped it over millennia.


One significant discovery in this realm comes from Gale Crater, believed to have been an ancient lake approximately 3.8 billion years ago, formed from an asteroid impact.

Analysis of sediments collected by the Curiosity rover from this site uncovered organic matter. Intriguingly, this organic matter was found to contain a lower ratio of the carbon-13 isotope (13C) to carbon-12 (12C) compared to that typically found on Earth, sparking questions about the formation processes of organic material on Mars.

A recent study published in the journal Nature Geoscience, offers new insights into this anomaly. Led by Professor Yuichiro Ueno from the Tokyo Institute of Technology and Professor Matthew Johnson from the University of Copenhagen, the research team proposes that the discrepancy in isotopic composition can be explained by the photodissociation of carbon dioxide (CO2) in Mars' atmosphere.


Explaining their findings, Ueno notes, "The Martian organic matter shows a 13C abundance of 0.92% to 0.99% of the total carbon content, which is considerably lower compared to Earth’s sedimentary organic matter at about 1.04%, and atmospheric CO2 at around 1.07%."

These values are unlike the organic matter found in meteorites, which typically show about 1.05% 13C.


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The team's research began by examining the atmospheric conditions of early Mars, which was predominantly composed of CO2 containing both 13C and 12C isotopes.

Through laboratory simulations mimicking the Martian atmosphere’s composition and temperature, the scientists discovered that when 12CO2 is exposed to solar ultraviolet (UV) light, it preferentially absorbs this radiation and dissociates into CO depleted in 13C, while leaving behind CO2 enriched in 13C.


This process of isotopic fractionation, where different isotopes of the same element are separated, has been observed in the upper atmospheres of both Mars and Earth. On Earth, UV radiation from the sun causes CO2 to split into CO that is depleted in 13C. On Mars, this phenomenon has more profound implications due to the planet's unique atmospheric conditions and history.

In Mars' reducing atmosphere, the CO generated from this process can further transform into simple organic compounds, such as formaldehyde and carboxylic acids. During the era when Mars potentially had surface temperatures close to water's freezing point, these organic compounds could have dissolved in liquid water and eventually settled in the sediments that are now being analyzed by scientists.


The research team's model calculations suggest that if Mars' atmosphere had a CO2 to CO ratio of 90:10, with a 20% conversion rate of CO2 to CO, it would result in sedimentary organic matter with δ13CVPDB values of -135‰, and the remaining CO2 would show δ13CVPDB values of +20‰. These figures closely match those found in Martian sediments examined by the Curiosity rover and in studies of Martian meteorites.

This evidence strongly suggests that the formation of organic matter on early Mars was primarily driven by atmospheric rather than biological processes. This insight is crucial for our understanding of Mars' past habitability and the potential for life.

Professor Ueno emphasizes the broader implications of their findings, stating, "If the estimations in this research are correct, there might be a surprising amount of organic material present in Martian sediments. This suggests that future explorations of Mars might uncover large quantities of organic matter."


Such discoveries could significantly enhance our understanding of Mars' geological and potentially biological history, laying the groundwork for future missions to unravel the mysteries that still remain about this intriguing planet.

For more science and technology stories check out our New Discoveries section at The Brighter Side of News.


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