Perseverance finds surface carbon on Martian rocks
A new study says the rover detected complex carbon at a Jezero Crater outcrop, but scientists cannot yet say whether it came from life or chemistry.
By Maya Lindqvist · Senior Technology Correspondent
3 min read
NASA’s Perseverance rover has detected complex macromolecular carbon on the surface of rocks at the edge of an ancient Martian river channel. The finding, reported in Science Advances, gives scientists a new target in the search for chemical traces from Mars’ distant past, though the team says it cannot yet identify the carbon’s origin.
The rover made the detection at Bright Angel, an outcrop near Neretva Vallis in Jezero Crater, where Perseverance has spent five years examining rocks for signs of past processes on Mars. Ashley E. Murphy, a researcher at the Planetary Science Institute in Tucson, Arizona, and lead author of the study, said the team believes it is the shallowest detection of organic matter yet made on the Martian surface.
Perseverance has previously found organic carbon, according to the study team, but mostly after drilling into rocks or scraping their surfaces. At Bright Angel, the carbon signal came from material exposed on the rock surface.
The detection came from SHERLOC, a deep-ultraviolet Raman and luminescence spectrometer mounted on the rover’s robotic arm. The instrument fires a laser at a target and analyzes shifted light signals that reveal molecular bonds.
Between Martian sols 1180 and 1218, the rover examined four targets at Bright Angel. The study says one target, Steamboat Mountain, served as a nearby control, while three others, named Cheyava Falls, Apollo Temple and Walhalla Glades, produced a signal known as a graphitic band, or G-band.
According to the researchers, that signal points to a cross-linked network of mostly reduced carbon atoms that can resist chemical and heat-driven breakdown. Murphy said the material resembles terrestrial kerogen within the limits of Perseverance’s instruments, but the team avoided using that term because on Earth it is tied strongly to biological material, especially buried fossil microbes.
The study says the Martian material could still have formed without life. Murphy said “macromolecular carbon” leaves open whether the material came from biological or non-biological processes.
The team also checked whether the signal could have come from the rover rather than the rocks. Kyle Uckert, SHERLOC’s deputy principal investigator at NASA’s Jet Propulsion Laboratory, and colleagues tested spare flight optics in the lab, used Martian calibration targets and collected background readings after a dust-cover anomaly forced SHERLOC into a new operating mode.
Uckert said nearby rock targets did not show the same G-band signal, including Steamboat Mountain. The researchers also considered contamination from Earth, but noted that Perseverance’s abrasion bit was sterilized before launch and had been used elsewhere in Jezero without producing a similar strong signal.
Cheyava Falls strengthened that case, according to the study, because the rover did not touch it with the abrasion hardware and only cleared dust from the surface with nitrogen gas. Uckert said the control rock showed no spectral evidence of organic matter.
The chemistry around the carbon varied by site. Murphy said that difference suggests carbon may have been emplaced during at least two episodes over geologic time.
At Apollo Temple, the carbon signal appeared with carbonate and sulfate minerals, which can form when water moves through older rock, according to the study. At Walhalla Glades, the carbon was found in silicate-rich sediment, which Murphy said could fit an earlier phase when organic matter settled into lake mud and was later buried.
Kevin P. Hand, Perseverance principal investigator at JPL, said Earth-based laboratories would be needed to test the samples with methods beyond the rover’s payload. He said isotope measurements, molecular handedness and powerful microscopy could help scientists assess whether the carbon records ancient Martian life.
The study also identifies non-biological possibilities, including fluid-rock reactions that can create organic compounds. Hand said Perseverance is now exploring rocks outside Jezero Crater that may be among the oldest ever studied by a rover on Mars, where early-life clues could still be preserved if life arose there.
This story draws on original reporting from Ars Technica.