NASA’s rover landed on Mars on Aug. 6, 2012, and since then has roamed Gale Crater, taking samples and sending the results back home for researchers to interpret. Analysis of Carbon isotopes in sediment samples taken from half a dozen exposed locations, including an exposed cliff, leave researchers with three plausible explanations for the origin: cosmic dust, ultraviolet degradation of dioxide, or ultraviolet degradation of biologically produced methane.
The researchers note today in Proceedings of the National Academy of Sciences that all three of these scenarios are unconventional, unlike processes common on Earth. Carbon has two stable isotopes, 12 and 13. By looking at the amounts of each in a substance, researchers can determine specifics about the cycle that occurred, even if it happened a very long time ago.
Curiosity heated the samples in the absence of oxygen to separate any chemicals. Analysis of a portion of the reduced produced by this pyrolysis showed a wide range of Carbon 12 and 13 amounts depending on where or when the original sample formed. Some was exceptionally depleted in 13, while other samples were enriched.