Rocknest, where Curiosity scooped its soil sample. Photo: NASA

In short, carbon.

Specifically, chlorinated methane gas, which contains carbon. Curiosity’s Sample Analysis at Mars (SAM) instrument also found traces of water, sulfur, and perchlorate salts, but naturally the building blocks of organic matter is what could be the most exciting discovery. Now, researchers are trying to work backwards to see if these carbon atoms could be the remains of life.

There are few pitfalls here. It’s possible that the carbon traces come from the rover itself, since NASA couldn’t completely clean it of every extraneous molecule before lift off. It’s also possible that the carbon came from meteorites and comets that slammed into the planet.

What researchers think happened was some molecular re-arranging in the SAM. SAM works like this: The microwave-sized machine heats up the matter Curiosity collects from the soil. Then it analyzes the vapors that the cooking soil emits and uses a laser spectrometer to examine atoms. The team thinks the sizzling perchlorates in the sample released chlorine, a sticky atom that easily bonds with molecules like carbon dioxide, and that’s what may have made the chlorinated methane.

Researchers at NASA say they need to remain patient. The problem with organic compounds is that they’re easily destroyed, whether by cosmic radiation, perchlorate salts or hydrogen peroxide. If the team wants to find carbon compounds, the rover will more likely have to dig a little deeper into Mars.

This plot of data from NASA’s Mars rover Curiosity shows the variety of gases that were released from sand grains upon heating in the Sample Analysis at Mars instrument, or SAM. The gases detected were released from fine-grain material, and include water vapor, carbon dioxide, oxygen and sulfur dioxide. (NASA/JPL-Caltech/GSFC)

Scientists indicate the oxygen and chlorine may come from perchlorate or similar compounds, which contain chlorine and oxygen. (NASA/JPL-Caltech/GSFC)

(NASA/JPL-Caltech/GSFC)