A year ago, the Perseverance rover found something puzzling in Jezero Crater: sedimentary rocks showed chemical patterns similar to those on Earth often associated with ancient microbial activity. The scientists were extremely cautious. Those The signs did not prove the existence of past life, but they were unusual enough to merit further investigation.
Now a new piece of the puzzle has appeared. A study published in Science Advances reveals that these same rocks contain complex organic carbon, a type of especially interesting material for astrobiology because it constitutes one of the fundamental ingredients of the chemistry of life.
And most importantly: the carbon appears in exactly the same place where Perseverance previously detected those possible biosignatures. The samples come from the Bright Angel outcrop, located in an ancient river channel that emptied into the Jezero Crater billions of years ago. Today the landscape is a frozen and dusty desert. But in the past, Jezero was home to a lake fed by rivers. Its sediments accumulated layer after layer, just as happens in terrestrial deltas.
The study’s authors, led by Ashley Murphy of the Planetary Science Institute, consider these environments especially promising because fine mud can trap and preserve organic molecules for enormous periods of time. So what exactly did the rover find? Using the SHERLOC Raman spectrometer, Perseverance analyzed two Martian mudstones. In one of them, the organic carbon appeared integrated within a matrix rich in silicates, that is, minerals that were part of the original rock.
In the other, carbon was associated with secondary carbonate and sulfate minerals, formed later by the action of water. The study also highlights an important detail: the organic material does not seem to be strongly degraded. That could mean that was exposed to the surface relatively recently or has resisted Martian radiation and oxidation surprisingly well.
The key word is “could.” The discovery does not prove that there was life on Mars. The authors themselves emphasize that Carbon can have several possible origins, as material contributed by meteorites and interplanetary dust, geological processes that occurred within the planet or ancient biological processes. Mars has various mechanisms capable of generating organic molecules without the intervention of living organisms, including hydrothermal reactions, volcanic processes and chemical transformations of carbon dioxide.
So why is it so important? Because the evidence begins to coincide in the same place. Now astrobiologists, planetary geologists and chemistry experts have sediments deposited in an ancient aquatic environment, chemical patterns compatible with possible biological interactions and, the latest discovery, complex organic carbon preserved in those same rocks. In planetary science, the spatial coincidence of several independent clues is often much more valuable than a spectacular but isolated observation. But the study also points out another relevant aspect.
The detections of organic matter made by Perseverance are separated by more than 3,500 kilometers from those that the Curiosity rover found years ago in Gale Crater. That suggests that The availability of organic compounds could have been widespread over large regions of ancient Mars and not limited to a single enclave exceptional. In other words, if Mars was once habitable, that habitability may not have been a local phenomenon.
Paradoxically, Perseverance’s most exciting discovery cannot yet be answered on Mars. Murphy’s team acknowledges that To determine the exact origin of the carbon, it will be necessary to analyze the samples with instruments much more sensitive than those carried by the rover.. That will only be possible if the rocks collected by Perseverance are brought to Earth on a future sample return mission.
It is true that no piece of evidence alone is enough to solve the case, but each new piece of evidence reduces the space of possible explanations a little more. And now we know that, in the heart of an ancient Martian river, Perseverance has found complex organic carbon exactly where some of the most intriguing signals in all of the exploration of the red planet had already appeared. In a nutshell: Mars remains unrevealed if it was ever alive. But it is becoming increasingly difficult to ignore the chemical traces it left behind.