Perseverance strikes again with an intriguing — yet unresolved — clue in the search for past life on Mars.
In an ancient river channel, the rover detected complex organic carbon within and on rocks, planetary scientist Ashley Murphy and colleagues report June 24 in Science Advances. One of those detections is the first of their kind to be found on a rock the rover hadn’t drilled into. Combined with previous data from Perseverance, the finding adds context to a potential signature of long-ago microbial processes on Mars, says Murphy, of the Planetary Science Institute headquartered in Tucson, Ariz.
Perseverance took these measurements in July 2024, when the six-wheeled robot found organic-rich “leopard spots” at the same site. These spots sparked wide interest due to the mineral content of their rims — iron phosphate — which bore similarities to features on Earth known to typically be associated with ancient microbial life.
The newly described organic carbon detections are from the same 2024 measurements, but they represent a deeper dive using a different instrument on the rover, SHERLOC, to characterize the carbon found in the rocks and give details about its texture.
SHERLOC measured four targets across three rocks at Bright Angel, a rock formation in the dried-up river that fed the ancient lake now called Jezero crater. The measurements revealed that this organic carbon is mixed in with both the silicate-dominated sediment and later-forming carbonate and sulfate minerals. This suggests the organics may have been emplaced at two different points in the rocks’ history — as the sediments were first laid down, and later as fluids moved through and altered the rock. These data, however, cannot reveal the origin of the organic carbon, Murphy says.
Planetary scientist Paul Byrne of Washington University in St. Louis says the organic carbon “could be from meteorites or cosmic dust; abiological processes like hydrothermal reactions; or they could be biological in nature.”
Still, the detection of organic carbon in Bright Angel could have compelling implications in the search for ancient microbial Martians. In 2014, seven years before Perseverance landed in Jezero crater, the Curiosity rover detected organics at Gale crater, more than 3,500 kilometers away. The location of the Gale crater organics so far from Perseverance’s organics could indicate that if life ever existed on Mars, it may have been widespread.
To determine whether the samples collected by Perseverance are signs of ancient life, they need to be analyzed on Earth — the rover doesn’t have the instruments needed to characterize the organic carbon’s structure and identify the clusters of atoms attached to it. Perseverance has cached 30 samples for possible return to Earth, including a rock core dubbed Sapphire Canyon that contains the organic carbon. But budget cuts and shifting priorities have complicated plans for bringing the Martian samples home.
Any knowledge gleaned from these samples is worth pursuing, Byrne says. If laboratory analyses reveal that the molecules formed abiotically, that would enhance scientists’ understanding of how complex organic chemistry can function sans life.
“Or perhaps we’ll find … that these compounds were produced by alien biology,” he says. “That possibility is worth bringing these samples back to Earth.”
