Key facts
- NASA's Perseverance rover detected complex macromolecular carbon on the surface of a Martian rock.
- The carbon signature, known as the graphitic band (G-band), indicates a network of reduced carbon atoms.
- The material is resistant to chemical and thermal breakdown and roughly matches terrestrial kerogen.
- Researchers ruled out instrument hardware malfunction and rover contamination as sources for the signal.
- The carbon's association with different mineral types suggests multiple emplacement events.
- Further analysis of returned samples is needed to determine if the carbon is of biological or abiotic origin.
NASA's Perseverance rover has detected complex macromolecular carbon on the surface of a Martian rock at the Bright Angel site, an outcrop on the edge of the Neretva Vallis ancient river channel. This marks the shallowest detection of organic matter on the Martian surface to date. The discovery was made using the SHERLOC instrument, which analyzes light reflected from a target after being hit by a UV laser. Scientists identified a spectroscopic signature indicating a tangled, cross-linked network of reduced carbon atoms resistant to breakdown, similar to terrestrial kerogen. However, researchers are hesitant to label it as biogenic, as the term kerogen implies a biological origin, and they are considering abiotic processes as well. Initial concerns about the signal originating from the instrument's hardware or from contamination brought by the rover were addressed through rigorous testing and control measurements, including examining spare optics and known calibration targets, and noting that nearby rocks did not show the same signal. The abrasion bit used by the rover was sterilized before launch and had not produced such a strong signal in previous uses. Furthermore, one rock target was analyzed after simply being cleared of dust with nitrogen, without physical contact from the rover's hardware. The chemical analysis of the material adjacent to the carbon suggests that its emplacement may have occurred during at least two distinct geological events. At one site, the carbon signal clustered with carbonate and sulfate minerals, indicative of precipitation from water, while at another, it was found within silicate-rich sediment. This suggests a history involving organic matter settling into ancient lake mud and later being altered by groundwater. Ultimately, distinguishing between a biological and abiotic origin will likely require sample return to Earth, where more advanced techniques can be employed to analyze isotopic signatures, chirality, and potential microfossils. Scientists noted that the Perseverance rover's instruments are designed to identify compelling samples for return, rather than definitively determine the origin of organic compounds on Mars.