Carbon Molecules on Mars Open New Mystery

A greatly reduced carbon 13 signature is discovered in a drill sample taken by NASA’s Curiosity rover on Vera Rubin Ridge in Gale Crater.

IMAGE: A selfie taken by NASA’s Curiosity Mars rover on Sol 2291 at the “Rock Hall” drill site, located on Vera Rubin Ridge. Reduced carbon released from powder from this drill hole was strongly depleted in carbon 13, the surprising carbon isotopic signature reported by the team. The selfie is composed of 57 individual images taken by the rover’s Mars Hand Lens Imager (MAHLI), a camera on the end of the rover’s robotic arm. CREDIT: NASA/Caltech-JPL/MSSS

Scientists have been analyzing recent data collected by NASA’s Curiosity rover that has led to headlines everywhere being less than circumspect and a little clickbait-y.

While analyzing samples taken from the Highfield drill hole on Vera Rubin Ridge in Gale Crater, researchers found what they have deemed an “intriguing” carbon signature. They found that the powder in this sample was strongly depleted in carbon 13, one of two stable carbon isotopes. Here on Earth, depletion of this sort can be caused by the ultraviolet degradation of biological methane.

Take a moment to giggle over cow farts, and then let’s move on.

How do we know the sample is reduced in this particular isotope? Christopher H. House, lead author of the new paper in the Proceedings of the National Academy of Sciences, explains: The amounts of carbon 12 and carbon 13 in our solar system are the amounts that existed at the formation of the solar system. 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.

So Curiosity samples a rock by drilling into its surface. Then another instrument heats that sample to separate out various chemicals. Finally, the sample is analyzed spectrographically, and the spectra tell us what was actually in the sample, including the relative proportions of different isotopes. They compare those proportions with what is already known to exist in our solar system, and voila, carbon 13 is relatively absent.

IMAGE: This image shows the Highfield drill hole made by NASA’s Curiosity rover as it was collecting a sample on Vera Rubin Ridge in Gale crater on Mars. The image was taken by the Mars Hand Lens Imager on the 2,247th Martian day, or sol, of the mission. CREDIT: NASA/Caltech-JPL/MSSS.

Now, about those headlines. Yes, on Earth, we see a depletion of carbon 13 due to the breakdown of biogenic methane, whose composition is CH4 — one carbon to four hydrogen. The methane is broken down, and the carbon escapes into the atmosphere. However, there are two other possibilities for this process: a cosmic dust cloud or that same…