NASA has uncovered “intriguing” carbon signatures on Mars after analyzing powdered rock samples collected by the Mars Curiosity Rover.
In an article posted to the official NASA website on Jan. 17 NASA scientists “announced that several samples collected by the rover are rich in a type of carbon that on Earth is associated with biological processes.”
Scientists were quick to note that the discovery doesn’t “necessarily” point to ancient life on Mars, stating that they have “not yet found conclusive supporting evidence of ancient or current biology there, such as sedimentary rock formations produced by ancient bacteria, or a diversity of complex organic molecules.”
Paul Mahaffy, the principle investigator of the Sample Analysis at Mars chemistry lab said, “We’re finding things on Mars that are tantalizingly interesting, but we would really need more evidence to say we have identified life.”
NASA’s findings are to be published in the Proceedings of the National Academy of Sciences journal on January 18 where scientists are expected to offer several explanations for the unusual carbon signals. Their theories are drawn in part from carbon signatures observed here on Earth; however, scientists are warning that the two planets are so different that they will be unable to make definitive conclusions based on Earth samples.
‘The hardest thing’
“The hardest thing is letting go of Earth and letting go of that bias that we have and really trying to get into the fundamentals of the chemistry, physics and environmental processes on Mars,” said Goddard astrobiologist Jennifer L. Eigenbrode.
One hypothesis for the curious signatures is that ancient bacteria on the surface could have produced a unique carbon signature as they released methane into the Mars atmosphere. Once in the atmosphere this methane would have been exposed to ultraviolet light that would have converted the gas into “larger, more complex molecules.” These molecules would have rained down to the surface of the planet and could be preserved, with their distinct carbon signature, in Martian rocks.
While the discovery of ancient life on Mars would be an Earth shattering revelation, scientists are also offering up nonbiological explanations.
One theory puts forward the idea that the carbon signature could have resulted “from the interaction of ultraviolet light with carbon dioxide gas in the Martian atmosphere, producing new carbon-containing molecules that would have settled to the surface.”
Another theory is that the carbon could have been left behind from a rare event millions of years in the past, when a giant molecular cloud rich in carbon passed through the solar system, depositing the carbon on the Mars surface.
Christopher House, a Curiosity scientist based at Penn State who led the carbon study believes that “all three explanations fit the data,” leaving the possibility open that the signatures detected could be the result of ancient life on the planet.
House’s team used the Tunable Laser Spectrometer (TLS) instrument located at the SAM lab to analyze the samples. The instrument can differentiate between different forms of carbon. The carbon 12 atom, for instance, is used by nature to metabolise food or is used by lifeforms for photosynthesis.The carbon 13 atom on the other hand is a heavier form of carbon found in ancient rocks. The two forms of carbon are the only two of five that are known to man that are not radioactive or a byproduct of a nuclear reaction.
Researchers found that nearly half of the samples analyzed had a “surprisingly large amount of carbon 12 compared to what scientists have measured in the Martian atmosphere and meteorites,” supporting the idea that the samples were a result of ancient life.
Andrew Steele, a Curiosity scientist based at the Carnegie Institution for Science in Washington, D.C. noted that scientists are just beginning to understand how the carbon cycle works on Mars and how to interpret isotopic ratios and the nonbiological activities that could lead to those ratios.
“Defining the carbon cycle on Mars is absolutely key to trying to understand how life could fit into that cycle,” Steele said. “We have done that really successfully on Earth, but we are just beginning to define that cycle for Mars.”
Going forward, NASA scientists are going to collect samples from other sites on the planet to see if they can detect a similar carbon signature to further test the biological hypothesis.
This discovery will be used as “guidance to the team behind NASA’s Perseverance rover on the best types of samples to collect to confirm the carbon signature and determine definitively whether it’s coming from life or not.”