Exploring the origins of life on Mars

The researchers from the University of Copenhagen and Tokyo Institute of Technology relate these findings to photolysis, in which ultraviolet light from the sun breaks down carbon dioxide, leading to the formation of non-living organic matter.

Two samples from Mars together represent the “smoking gun” in a new study that shows the origin of organic matter on Mars. The research provides strong evidence for a prediction made more than a decade ago that could hold the key to understanding how organic molecules, the building blocks of life, formed on Earth.

The findings of the Curiosity rover show that organic matter could have been formed by the photolysis of carbon dioxide, suggesting an abiotic origin. This finding, linked to research from the University of Copenhagen, supports theories about the common past of the Earth and Mars atmospheres and points to processes that could have led to the emergence of life.

A robot is moving on its own in a meteor crater on the Red Planet. For now, it may be collecting soil samples with a drill and a robotic arm, as this requires a lot of practice. NASA’s Curiosity rover has been active as the Mars Science Extension Arm for nearly 12 years and continues to make discoveries that surprise and challenge scientists’ understanding of Mars and the Earth world.

Recently, the discovery of organic deposits with peculiar properties has left many researchers scratching their heads. The properties of this carbon-based material, especially its carbon isotope ratio, surprised the researchers.

“If organic material with such properties is found underground, it usually indicates the presence of microorganisms, but they can also be the result of abiotic and chemical processes. This discovery obviously has researchers looking for definitive answers, but there don’t seem to be any suitable answers.”

New insights and theoretical advances

Yet there’s nothing fraught about the research collaboration behind a new study published in the journal Nature Geoscience, and there’s plenty of enthusiasm.

In fact, the discovery on Mars provided the missing piece for this team of researchers from the University of Copenhagen and Tokyo Institute of Technology to make everything fall into place.

As author and chemistry professor Matthew Johnson put it, this was the “ironclad evidence” needed to confirm his theory from a decade ago about so-called photolysis in the Martian atmosphere.

Using the example of Curiosity, new research was able to prove with reasonable certainty that the Sun broke down carbon dioxide in the Martian atmosphere billions of years ago, just as old theories predicted. The resulting carbon monoxide gradually reacted with other chemicals in the atmosphere to form complex molecules that gave Mars its organic matter.

“In addition, since the CO2 atmospheres of Earth, Mars and Venus were very similar when the photolysis occurred long ago, this may also be important for our understanding of the origins of life on Earth,” says Professor Matthew Johnson from the Department of Chemistry at the University of Copenhagen.

A puzzle solved

Twelve years ago, Johnson and two colleagues used simulations based on quantum mechanics to determine what happens when an atmosphere rich in carbon dioxide is exposed to ultraviolet sunlight, a process called photolysis.

Basically, on Mars, about 20% of CO 2 is broken down into oxygen and carbon monoxide. But carbon has two stable isotopes: carbon-12 and carbon-13. Normally, they exist in a ratio of 1 carbon-13 to every 99 carbon-12. However, the lighter carbon-12 photolyzes faster, so carbon-13 photolysis produces less carbon monoxide (depletion) and leaves more CO 2 (enrichment).

Because of this, Johnson and his colleagues were able to make very accurate predictions about the carbon isotope ratios after photolysis, giving them two different fingerprints to look for. One of them was discovered several years ago in a different sample from Mars.

Linking Mars samples to photolysis theory

“We actually have a piece of Mars here on Earth that was ejected from Mars by a meteorite and then re-emerged as itself when it landed on Earth,” said Matthew Johnson. The meteorite, named Allen Hills 84001 after the site in Antarctica where it was found, contains carbonate minerals that formed from carbon dioxide in the atmosphere. The smoking gun here is that the ratio of carbon isotopes in it is exactly what we predicted in our quantum chemistry simulations, but there was a missing piece of the puzzle. We were missing another product of the chemistry to confirm the theory, and this is what we have now.

The carbon in the Allan Hills meteorite is enriched in carbon-13, making it a mirror image of the carbon-13 depletion measured in organic matter found on Mars by NASA’s Curiosity rover; the new study therefore links data from two samples that the researchers believe had the same origin during Mars’ childhood but were separated by more than 50 million kilometers.

“There is no other way to explain the carbon-13 depletion in organic matter and the carbon-13 enrichment in Martian meteorites that is not related to the composition of volcanic carbon dioxide emitted on Mars, which has a similar fixed composition to Earth’s volcanoes,” Johnson said.

Future research and the complexity of Earth’s geology

Because organic matter contains isotopic “fingerprints” of its origin, the researchers were able to trace the carbon in the organic matter to the source of carbon monoxide formed by photolysis in the atmosphere. But it also revealed a lot about what was going on in the meantime.

“This suggests that carbon monoxide is the starting point for the synthesis of organic molecules in these atmospheres; thus, we have an important conclusion about the origin of the building blocks of life,” Johnson said.

Johnson explained that researchers would like to find the same isotopic evidence on Earth, but this has not yet happened and may be a greater challenge because our geological development has significantly altered the surface compared to Mars.

“It is reasonable to assume that the photolysis of CO 2 was also a prerequisite for the emergence of life on Earth, regardless of its complexity,” says Matthew Johnson. But we have not yet found such “ironing proof” material on Earth to prove that this process took place. Perhaps it is because the Earth’s surface is more active, both geologically and literally, and therefore constantly changing. But it is a big step forward from what we have now found on Mars, because the two planets are very similar.