Several of the samples collected by Mars rover Curiosity are found to be rich in the kind of carbon created on Earth by biological processes.

Mars rover Curiosity has been in Gale crater on the red planet for nearly a decade. In that time, the rover has already examined a lot of rocks. After a new analysis, researchers are now making an exciting discovery. Because several of the samples collected by Mars rover Curiosity appear to be rich in the kind of carbon that is created on Earth through biological processes.

Carbon-12

Carbon is particularly important because this element is associated with all life on Earth; it flows continuously through the air, water and ground. Carbon has two stable isotopes: carbon-12 and carbon-13. Living things on Earth use the smaller, lighter carbon-12 atom for the conversion of food or for photosynthesis. And now, researchers have found that nearly half of the rocks that Mars rover Curiosity has sampled over time contain carbon-12. These samples come from five different spots in Gale Crater.

This image shows a borehole made by NASA’s Curiosity rover. The Mars rover collected a sample of the rock on Vera Rubin Ridge (a high and steep hill) in Gale Crater. Powder from this hole appears to be rich in carbon-12. Image: NASA/Caltech-JPL/MSSS.

Extraterrestrial life

Although it’s an intriguing find that could just hint at extraterrestrial life, the researchers remain sober. According to them, the discovery does not necessarily indicate former life on Mars. That’s because scientists haven’t yet found conclusive supporting evidence, such as sedimentary rock formations formed by ancient bacteria, or a diversity of complex organic molecules. “We find things on Mars that are tantalizingly interesting,” said study researcher Paul Mahaffy. “But we really need more evidence to confirm that we’ve discovered life.”

Three explanations

In their study, the researchers come up with three explanations for the unusual carbon detected; one based on a biological process and two non-biological explanations.

1) The first explanation is based on a biological origin. For example, the carbon traces could indicate that bacteria have been at work. Microorganisms may have released methane into the atmosphere, where this gas was then converted into larger, more complex molecules by ultraviolet. These new molecules then rained down on the surface, where they are preserved along with the carbon traces in Martian rock.

2) In addition, the discovered carbon traces may also have been created by an interaction between ultraviolet light and CO2 in the Martian atmosphere. This created new, carbon-containing molecules that sank to the surface.

3) Finally, the team speculates that the carbon could have been left behind by a giant molecular cloud rich in carbon-12. This cloud would have paid a visit to our solar system hundreds of millions of years ago.

“All three explanations fit the data,” said researcher Christopher House. “We simply need more data to confirm or disprove them.”

Carbon cycle

The next step is now to fully map the carbon cycle on Mars. Because that will already clarify a lot. “On Earth, the kind of carbon we discovered on Mars is biological in origin,” House says. “However, we need to understand whether the same explanation works for Mars, or whether there are other explanations. Mars is really very different.” So defining the carbon cycle on Mars is absolutely essential in trying to understand how life might fit into that cycle.

Research continues. For example, the Curiosity team plans to measure more carbon isotopes to see if the rover finds similar carbon tracks elsewhere. To test the biological explanation, the team wants to analyze the carbon content of a methane plume released from the surface. Curiosity encountered such a plume in 2019, although it is currently questionable whether that will happen again. There is also a task here for Mars rover Perseverance. Because if this rover succeeds in collecting the best kind of monsters, it can be definitively determined whether there is (or has been) life on Mars.