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The more scientists learn about Mars, the more intriguing the Red Planet becomes as a potential haven for primitive life in the ancient past ... and perhaps even the present.
A study released Monday (March 23) reports that ancient Mars harbored a form of nitrogen that could potentially have been used by microbes, if any existed, to build key molecules such as amino acids. An unrelated study suggests that atmospheric carbon monoxide has been a feasible energy source for microbes throughout the Red Planet's history. Both papers were published Monday in the journal Proceedings of the National Academy of Sciences (PNAS).
"It's more support for this environment that would have had the ingredients that life would have needed," said Jennifer Stern of NASA's Goddard Space Flight Center in Greenbelt, Maryland, lead author of the nitrogen study. [The Search for Life on Mars: A Photo Timeline]
All life on Earth requires nitrogen, which is a critical component of amino acids and other biomolecules. But microbes can't just pull their nitrogen straight out of the air; atmospheric, or molecular, nitrogen (N2) features two atoms of the stuff linked in a tight triple bond, making it relatively inert and inaccessible.
Before life-forms can incorporate nitrogen into their metabolic processes, that bond must be broken; nitrogen must be "fixed" into different, more chemically reactive compounds, such as nitrate (NO3).
That process did indeed occur on Mars, Stern and her team reported in their study, which looked at measurements made by the Sample Analysis at Mars (SAM) instrument aboard NASA's Mars rover Curiosity.
SAM found significant concentrations of nitrate in soil and rock samples that Curiosity collected at three different spots near its landing site — Rocknest, John Klein and Cumberland.
The John Klein and Cumberland samples, which were drilled from a sedimentary mudstone, had previously allowed rover team members to conclude that, billions of years ago, the area was part of a potentially life-supporting lake-and-stream system. The discovery of fixed nitrogen contributes to this habitability picture.
"Had life been there, it would have been able to use this nitrogen," Stern told Space.com. [Ancient Mars Could Have Supported Life (Photos)]
Life as we know it needs certain basic building chemical blocks (such as carbon and fixed nitrogen), liquid water and an energy source. In the other new PNAS paper, Gary King of Louisiana State University suggested that carbon monoxide (CO) could serve as an energy source on Mars, from ancient epochs all the way up to the present day.
While CO is toxic to many organisms, including humans, here on Earth, some microbes use it to drive their metabolism, gaining energy by oxidizing the substance into carbon dioxide (CO2).
Such life-forms are taking advantage of a relatively scarce resource, as Earth's atmosphere is just 0.3 parts per million (ppm) or so CO by volume. The Martian atmosphere, in comparison, contains 800 ppm CO currently, and concentrations of the stuff may have been much higher in the past. Therefore, CO seems like a plausible candidate for an energy source for Mars life, but the possibility hasn't drawn much scholarly attention, King wrote in the PNAS paper.