Somewhere in the dried bed of an ancient Martian river, the Perseverance rover has been drilling into rocks for more than four years — and last June, NASA scientists announced that two of them contain the same complex carbon-based molecules that form the building blocks of life on Earth

A paper published in Science Advances on 24 June 2026 reports the detection of complex organic carbon in two ancient mudstones examined by NASA’s Perseverance rover in Jezero crater. The material is macromolecular carbon, a class of large, cross-linked carbon molecules that on Earth is tied up with the chemistry of living things. The study, led by Ashley Murphy of the Planetary Science Institute and co-led by Kyle Uckert, deputy principal investigator for the rover’s SHERLOC instrument, describes hundreds of organic detections across the rocks and calls it the most robust organic result from Jezero so far.

The rocks lie in the Bright Angel outcrop, a light-toned formation along Neretva Vallis, the river channel that once carried water and sediment into Jezero’s western delta billions of years ago. One of the two is Cheyava Falls, the mudstone whose millimetre-scale mineral rings, nicknamed leopard spots, NASA drew attention to in September 2025.

What SHERLOC detected

SHERLOC is a deep-ultraviolet Raman spectrometer mounted on the rover’s robotic arm. It works by shining a laser at a rock surface and reading the light that scatters back, which lets it map minerals and organic compounds without grinding or drilling. The signature the team relied on is a pair of spectral features, the D-band and G-band near 1350 and 1600 wavenumbers, that mark macromolecular carbon.

Macromolecular carbon, or MMC, is a solid network of reduced carbon that resists heat and chemical breakdown. That durability lets it survive in rock for a very long time, which is what makes a near-surface detection worth attention.

The two mudstones together produced what the paper describes as the only detection of MMC on a natural rock surface on Mars to date. The Cheyava Falls reading came from a dust-cleared but otherwise unprepared surface, which the authors call the shallowest organic detection on the planet. Uckert has suggested the organics there may have been exposed relatively recently, or shielded by minerals with photoprotective properties.

Two rocks, two chemical settings

The detail worth dwelling on, in our reading, is not the carbon itself but its placement. In one rock, the organics are associated with secondary carbonate and sulfate minerals, the kind deposited later when fluids moved through the rock. In the other, they are bound up with the primary silicate matrix that formed when the mudstone itself was laid down.

That points to carbon incorporated through at least two separate processes at different times. Finding the same organic signal in both settings argues against a single delivery event and suggests organic chemistry was a recurring feature of ancient Jezero rather than a one-off.

Why building blocks are not the same as life

Building blocks of life is a fair description of the material, though it marks the edge of what the study will support. Macromolecular carbon arises through biological routes on Earth, but it also forms with no biology involved at all, through meteorite delivery, volcanic activity, and reactions in hot water. The Perseverance payload cannot tell the two apart.

Uckert has been plain about this. He has said the presence of organic matter on Mars does not necessarily imply biology, and that the study cannot claim biology played any role in the carbon it describes. The rover was not built to answer that question.

The Cheyava Falls rock has carried this ambiguity before. The September 2025 Nature paper led by Joel Hurowitz of Stony Brook University identified the same rock’s mineral features, including the leopard-spot reaction fronts rich in iron phosphate and iron sulfide, as a potential biosignature, a feature that could have a biological origin but need not. The June 2026 result adds organic carbon to that picture without resolving the origin of any of it.

The samples that cannot come home

Settling the question would take the kind of laboratory instruments no rover can carry, which means getting the cached cores back to Earth. That path narrowed sharply this year.

In January 2026, a congressional spending bill backed the White House’s move to end the Mars Sample Return programme, which had been the agency’s plan for retrieving Perseverance’s tubes. As reported in Science, the bill redirected the effort into a smaller Mars Future Missions line funded at $110 million, aimed at preserving landing and related technologies rather than mounting a retrieval. For now, the samples stay on Mars.

So the most spatially extensive organic detection yet made on Mars is sitting in sealed tubes on the surface, with the one measurement that could separate biology from geology out of reach and no funded mission to collect the cores. What to watch is whether a cheaper retrieval concept, a commercial partner, or China’s own sample-return plans change that arithmetic before Perseverance’s plutonium power source runs down.