Perseverance finds organic carbon beneath Mars

NASA’s Perseverance rover has found macromolecular organic carbon in two mudstone rocks inside Mars’s Jezero Crater, according to a study published June 24 in *Science Advances*. The detections came from the rover’s SHERLOC instrument, which mapped carbon-bearing material in rocks from the Bright Angel formation. The researchers said the finding adds to evidence that organic material can persist in ancient Martian rocks, but does not show that life existed on Mars. They said instruments on Earth would be needed to test the samples in greater detail. ### What exactly did Perseverance find in the rocks? The June 24 paper identified macromolecular carbon, or MMC, in two mudstones that Perseverance examined in an ancient river valley in Jezero Crater. The authors wrote that the measurements produced hundreds of organic detections, making this the most robust organic detection yet in Jezero and, to their knowledge, the only detection of macromolecular carbon on a natural rock surface on Mars. (science.org) Ashley Murphy, a co-lead author and postdoctoral researcher at the Planetary Science Institute, said in material describing the study that the result was “one of the most exciting findings to date.” Murphy and the team said the specific formation mechanism remains unknown. ### Why isn’t “organic carbon” the same thing as evidence of life? (science.org) Organic carbon is one of the chemical building blocks associated with life, but it can also form through nonbiological processes, the researchers said. The study and NASA-linked summaries both said the rover’s measurements cannot determine whether the material came from biology, geology, meteorites or other abiotic chemistry. (scitechdaily.com) Science Advances reported that the carbon was associated with different mineral settings in the two rocks. One rock showed organics alongside secondary carbonate and sulfate minerals, while the other showed organics associated with a primary silicate-dominated matrix. The authors said those patterns point to more than one possible emplacement or preservation event in Martian history. (scitechdaily.com) ### How close to the Martian surface was this material? Phys.org, summarizing the study from the participating institutions, reported that the macromolecular carbon was preserved only microns beneath the Martian surface. That is unusually shallow on a planet where radiation and oxidizing chemistry are expected to degrade complex carbon-bearing material over time. (science.org) SciTechDaily reported that the detection came from Bright Angel formation rocks that Perseverance examined with SHERLOC, a Raman and fluorescence instrument mounted on the rover’s arm. SHERLOC analyzes rock surfaces without destroying them and helps mission scientists decide which targets merit sampling. ### Why were these particular rocks important? (phys.org) Jezero Crater is the site of an ancient lake-and-delta system, and Perseverance was sent there to look for signs that microbial life might once have existed. The Bright Angel formation includes fine-grained mudstones laid down in water-rich conditions, according to the study summary, making them strong candidates for preserving chemical traces over long periods. (scitechdaily.com) The researchers said the carbon appeared with sediments deposited in the ancient environment and with minerals formed later during aqueous alteration. That combination is why the rocks are being treated as high-value targets for follow-up work. ### Can scientists test these rocks more directly? NASA says Perseverance is the first leg of the Mars Sample Return effort and is collecting and caching samples for possible return to Earth. (scitechdaily.com) The rover landed on Feb. 18, 2021, and NASA’s Jet Propulsion Laboratory said this week that it has collected 30 samples and still has six empty tubes. NASA’s current Mars Sample Return page now describes the campaign in the past tense as a proposed plan, while Perseverance’s own mission page still says the rover is collecting sealed samples for future pickup. (scitechdaily.com) That means the rover can keep building the sample collection even as NASA considers what return architecture, if any, comes next. ### What happens next for this discovery? (science.nasa.gov) Earth-based laboratories are the next step the researchers themselves identified. SciTechDaily’s summary of the study said more sensitive instruments on Earth would be required to determine whether the carbon has a biological or geological origin. Perseverance remains active in Jezero Crater, and NASA said the rover continues to collect detailed information about geologic targets it has not yet sampled. (science.nasa.gov) Any stronger claim about the origin of the newly reported carbon will depend on future analysis of returned material by scientists on Earth. (jpl.nasa.gov) (scitechdaily.com)