Scientists have now shown that carbon-rich molecules found in an ancient Martian lakebed once existed at far higher levels than the tiny traces measured today.
That revision means the planet must have produced or preserved far more carbon than expected, forcing a new accounting of how ancient Mars worked.
Carbon locked in mudstone
Deep within a dried lakebed on Mars, a sedimentary rock sample preserved three long carbon chains despite relentless surface radiation.
Using those molecules, Dr. Alexander A. Pavlov at NASA’s Goddard Space Flight Center calculated how much radiation would have destroyed and reconstructed their earlier abundance.
That reconstruction indicated the rocks once held substantially higher concentrations than the trace amounts measured today.
Those elevated starting levels now demand an explanation strong enough to account for both the preservation and the apparent loss over time.
What the rover found
Chemists call these chains alkanes, simple molecules made only of carbon and hydrogen, and they often survive heat.
Inside its laboratory, Curiosity identified gases released from the rock, and the pattern matched longer carbon chains.
Three related carbon molecules containing ten, eleven, and twelve carbon atoms appeared at roughly 30 to 50 parts per billion in the rock sample.
Lab work tied the trio to fatty acids, oily molecules that help build cell membranes, though nonliving chemistry can also make them.
Shelter from oxidation
Layered clays and sulfur-rich salts in mudstone can trap carbon compounds and keep them away from reactive oxygen.
When Curiosity warmed the sample in stages, early heating released oxygen first, so later heating did less burning.
Protected in mineral layers, the larger molecules stayed intact until high temperatures freed them for the rover to detect.
That kind of shelter makes some Martian rocks better targets than loose sand when scientists search for older chemistry.
Radiation sets a clock
On today’s Mars, thin air and weak shielding leave much of the surface under a constant stream of energetic particles from space.
That ionizing radiation, high-energy particles that break chemical bonds, can chop long carbon chains into smaller, harder-to-read fragments.
Over roughly 80 million years of radiation exposure, Pavlov’s team calculated that the rock may once have contained between 120 and 7,700 parts per million of these carbon molecules.
Once those starting numbers enter the picture, the hunt turns into a search for processes that can concentrate carbon.
Rewinding lost carbon
Lab irradiation results let Pavlov’s team estimate how fast organic molecules, carbon-based compounds made by life or geology, fall apart inside rock.
By combining that decay rate with the tiny amount measured today, the model inferred the earlier load.
Small changes in shielding depth or mineral mix can alter the math, which kept the reconstructed range broad.
That uncertainty still left room to check every plausible non-life source, then ask what was missing.
Non-life sources fall short
Processes called abiotic, made by chemistry without living organisms involved, can create carbon chains from dust, air, and rock.
Those sources sprinkle material broadly, yet radiation and reactive chemicals chew it up, so the pile rarely builds high.
“We argue that such high concentrations of long-chain alkanes are inconsistent with a few known abiotic sources of organic molecules on ancient Mars,” wrote Dr. Pavlov.
With familiar sources falling short, the team turned to two harder options that involve hot water chemistry or biology.
Guardrails on claims
Caution mattered because the rover saw only a few related molecules, not a full chemical signature that points one way.
Strong life claims need patterns that geology struggles to mimic, such as consistent ratios across many samples and layers.
“In addition, in practice with established norms in the field of astrobiology, we note that the certainty of a life detection beyond Earth will require multiple lines of evidence,” wrote Pavlov.
Until Mars missions can stack that evidence, the carbon chains stay a clue, not a verdict.
Simulating Mars conditions
Follow-up work now needs to track what radiation turns these molecules into inside mudstone, not just how fast they fade.
Laboratories can seal similar rocks in Mars-like air and temperature, then bombard them with particles that mimic cosmic rays.
Matching the breakdown leftovers to what Curiosity detects would tighten the clock and narrow the range of possible sources.
If an unknown nonliving pathway exists, its fingerprints should show up in those tests before anyone invokes ancient biology.
Why sample return matters
Bringing pieces of this mudstone to Earth would let labs run many checks that a rover cannot fit onboard.
High-precision instruments could compare isotopes, forms of the same element with different weights, across repeated measurements.
Perseverance has already cached samples for possible return, and those tubes could reveal whether the carbon chains repeat elsewhere.
Without that kind of cross-checking, any single site on Mars can fool scientists with local chemistry.
Where this leads
A trace of carbon chains, a protective rock, and a harsh radiation clock now point to a bigger ancient source.
Future lab work and returned samples can decide whether geology alone fits the numbers, or whether biology stays necessary.
The study is published in Astrobiology.
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