Curious clouds on Mars captured by the Curiosity Rover on the 3,063rd Martian day, or sol. Image Credit: NASA.

Signs of Life? Curiosity Measures Intriguing Carbon Signatures on Mars

The Curiosity Rover has measured a curious carbon signature on Mars. On Earth, this type of carbon is associated with biological processes—life.


Mars is one of the most similar places in the solar system to Earth. However, although the red planet may appear barren and lifeless, our understanding of what Mars was like in the distant past has dramatically changed.

While decades ago we thought it impossible for Mars to have been a world covered in water, lakes, and clouds, today we know that Mars was all that and perhaps much more based on numerous scientific missions on the red planet. Perhaps millions if not billions of years ago, Mars was a world that met all the requirements for life as we know it to exist on its surface.


But whether this was the case or not remains to be seen.

And significant progress is being made towards that goal with robotic missions on Mars such as Perseverance and Curiosity.

Anomalous carbon Reading on Mars, but is it life?

A recent report reveals that the analysis of carbon isotopes in sediment samples taken by the Curiosity rover shows an unusual carbon cycle on Mars that is nothing like what we see on Earth today.

“All three of these scenarios are unconventional, unlike processes common on Earth,” researchers explained in a study published in Proceedings of the National Academy of Sciences.

Martian soil samples obtained by the rover from half a dozen exposed locations in Gale Crater, including a cliff, leave researchers with three plausible explanations for the carbon’s origin.

Carbon has two stable isotopes, 12 and 13. So by looking at the amounts of each in a substance, researchers can determine details about the carbon cycle that occurred, even if it happened a long time ago, say billions of years ago.

“The amounts of carbon 12 and carbon 13 in our solar system are the amounts that existed at the formation of the solar system,” said Christopher H. House, professor of geosciences, Penn State.

“Both exist in everything, but because carbon 12 reacts more quickly than carbon 13, looking at the relative amounts of each in samples can reveal the carbon cycle.”

NASA’s Curiosity Rover has been studying and exploring Mars for nearly a decade after landing on the surface of the Red Planet on August 6, 2012.


The robotic rover has been exploring Gale Crater while talking multiple soul samples, sending back data for researchers on Earth to study.

The rover has been drilling into the Martian surface at Gale Crater, successfully recovering samples from buried sedimentary layers.

After analyzing one of the powdered rock samples gathered by Curiosity, researchers have said that several samples are rich in a type of carbon associated with biological processes—life—here on Earth.

While this may seem extraordinary, researchers say it does not necessarily point to the existence of ancient life on Mars.

Scientists have still not found conclusive evidence like sedimentary rock formations produced by ancient bacteria or complex organic molecules formed by life.

“We’re finding things on Mars that are tantalizingly interesting, but we would really need more evidence to say we’ve identified life,” revealed Paul Mahaffy, who served as the principal investigator of the Sample Analysis at Mars (SAM) chemistry lab aboard Curiosity until retiring from NASA’s Goddard Space Flight Center in Greenbelt, Maryland, in December 2021.

“So we’re looking at what else could have caused the carbon signature we’re seeing, if not life.”

In the study published in Proceedings of the National Academy of Sciences, researchers offer three possible explanations for the abnormal results of the powdered rock.

Explaining the Intriguing Carbon Signature on Mars

There is one biological explanation and two nonbiological explanations.

The first and most exciting is the biological explanations which essentially suggest that Mars was habitable in the distant past. Ancient Martian bacteria on the surface could have produced a unique carbon signature by releasing methane into the air.

This methane would then interact with ultraviolet light, turning into larger, more complex molecules. Eventually, these molecules would have rained down on the surface, remaining there until today, when Curiosity gathered soil samples.


The nonbiological explanations are not as exciting but equally plausible. For example, one of the explanations suggests that the “anomalous” carbon signature could have resulted from an interaction of ultraviolet light with carbon dioxide in the Martian atmosphere. These interactions would have produced new carbon-bearing molecules that were eventually deposited on the red planet’s surface.

The third nonbiological explanation proposes that the carbon in the samples was deposited on Mars as our solar system passed through a massive molecular cloud rich in the carbon detected by Curiosity’s instrument.

“All three explanations fit the data,” said House. “We simply need more data to rule them in or out.”

Why is the discovery of carbon so important? Well, this element is found in all life on Earth.

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Written by Ivan Petricevic

I've been writing passionately about ancient civilizations, history, alien life, and various other subjects for more than eight years. You may have seen me appear on Discovery Channel's What On Earth series, History Channel's Ancient Aliens, and Gaia's Ancient Civilizations among others.

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