It is not known whether life created carbon. This discovery strengthens the case for bringing samples home
Perseverance strikes again with an intriguing – but unsolved – clue in the search for past life on Mars.
In an ancient river canal, the rover detected complex organic carbon in and on rocksplanetary scientist Ashley Murphy and colleagues report June 24 in Scientific advances. One of these detections is the first of its kind to be found on a rock that the rover had not drilled into. Combined with previous data from Perseverance, the discovery adds context to a potential signature of ancient microbial processes on Mars, says Murphy, of the Planetary Science Institute headquartered in Tucson, Arizona.
Perseverance took these steps in July 2024, when the six-wheeled robot found organic-rich “leopard spots” at the same site. These sites attracted great interest because of the mineral content of their edges – iron phosphate – which bore similarities to features on Earth known to be commonly associated with ancient microbial life.
The newly described organic carbon detections come 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 rocks and give details of its texture.
SHERLOC measured four targets on three rocks at Bright Angel, a rock formation located in the dry river that fed the ancient lake now called Jezero Crater. The measurements revealed that this organic carbon is mixed with both the silicate-dominated sediments and the carbonate and sulfate minerals that form later. This suggests that the organic materials may have been emplaced at two different times in the rocks’ history: when sediments were first deposited, and then when fluids moved through and modified the rock. However, these data cannot reveal the origin of the organic carbon, explains Murphy.
Planetary scientist Paul Byrne of Washington University in St. Louis says the organic carbon “could come from meteorites or cosmic dust; from abiological processes like hydrothermal reactions; or even biological in nature.”
Nonetheless, 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 the Jezero craterthe Curiosity rover organic matter detected in Gale Cratermore than 3,500 kilometers away. The location of Gale Crater organics so far from Perseverance organics could indicate that if life ever existed on Mars, it could have been widespread.
To determine whether the samples collected by Perseverance are signs of ancient life, they must be analyzed on Earth – the rover does not have the instruments necessary to characterize the structure of organic carbon and identify the clusters of atoms attached to it. Perseverance cached 30 samples for a possible return to Earth, including a rocky core called Sapphire Canyon which contains organic carbon. But budget cuts and changing priorities have complicated plans to bring the Martian samples home.
All the knowledge gained from these samples is worth exploring further, Byrne says. If laboratory analyzes reveal that the molecules formed abiotically, it would improve scientists’ understanding of how complex organic chemistry can work without life.
“Or maybe we’ll discover… that these compounds were produced by extraterrestrial biology,” he says. “This possibility makes it worth bringing these samples back to Earth.”
