Newly discovered oxygen reaction could aid search for extraterrestrial life

Scientists have discovered a new way oxygen can form in the carbon dioxide-rich atmospheres of worlds beyond our own – challenging assumptions about how we should search for life on other planets , and perhaps about the origins of life itself.

“Most searches for life, or signatures of life, on other planets actually prove that everything we observe can be generated by means that do not require life,” David Benoit, lecturer in physics molecular and astrochemistry at the University of Hull. The EA Milne Center for Astrophysics, which was not involved in the study, told Space.com. “This study shows another pathway for molecular oxygen production that was not always considered viable before.”

Before the massive increase in atmospheric oxygen (O2) Earth During the Great Oxidation about 2.4 billion years ago, when ocean-dwelling cyanobacteria began producing oxygen through photosynthesis, our planet’s early atmosphere was dominated by carbon dioxide ( CO2) with only traces of oxygen.

“These O2 molecules were exclusively produced via abiotic (non-biological) processes,” writes the team of researchers led by Shan Xi Tian and Jie Hu of the University of Science and Technology of China.

Tian and Hu say they were fascinated by how this primitive atmospheric oxygen formed, reporting a new mechanism by which this could have happened.

Others, meanwhile, propose the formation of oxygen through mechanisms such as the so-called “three-body recombination” reaction of two oxygens. atoms or the dissociation of CO2 under ultraviolet light. It is also possible, some believe, that the substance came from specific reactions with electrons. “However, we found a distinctly different route to produce O2 from molecular CO2,” Tian told Space.com. “Namely, thanks to the reaction of helium ions (He+) with CO2.”

Most helium ions are produced when alpha particles in the solar wind interact with molecules in the upper atmosphere, creating charged particles called ions which then react with CO2 and could then form O2. “This reaction should be observed in the upper atmosphere of March“, because there are a lot of He+ ions (due to solar winds) and CO2,” Hu explained.

However, even though these reactions have been confirmed to create various ions, such as O+, O2+, and CO2+ in the Martian ionosphere, there is still no evidence that O2 is formed this way.

To prove their theory, the scientists used time-of-flight (TOF) mass spectrometry, a technique that determines the mass-to-charge ratio of ions in the gas phase by measuring the time they must travel a known distance inside an instrument called a spectrometer. This method is based on the principle according to which ions, accelerated by an electric field of known intensity, acquire different speeds depending on their mass/charge ratio and therefore reach the detector at different times.

But Hu and Tian went further, combining TOF with so-called “crossed beam devices” and “ion velocity maps” to try to elucidate all the possible mechanisms that would produce oxygen molecular. In this configuration, two particle beams – CO2 and He+ – crossed paths under controlled conditions, allowing reactions to occur at the point of collision.

The resulting products were ionized; their mass/charge ratios were determined based on the time it took them to reach the detector. Simultaneously, ion velocity mapping recorded the trajectories and velocities of the ions, providing detailed information about their energies.

Overall, the team was able to reconstruct the reaction pathways and gain essential insights into the step-by-step processes leading to the formation of oxygen from these two raw materials.

“This is a useful finding that demonstrates that a collision of helium with the types of energy we would see in solar winds can generate molecular oxygen when it encounters carbon dioxide,” he said. Benoit declared. “The efficiency of the process appears to be similar to that of the collision of carbon dioxide with low-energy electrons, studied a few years ago by the same research group.”

Because life on Earth is closely linked to oxygen concentrations, scientists have long studied atmospheric oxygen as a potential marker of habitability on other worlds, especially since most of the oxygen on Earth is produced by living organisms. However, this research demonstrates that oxygen can also be formed through abiotic processes or processes that are not rooted in living organisms. So if similar mechanisms operate on other planets with CO2-rich atmospheres, oxygen could exist even in the absence of life.

This discovery, however, does not mean that astronomers will jump to conclusions or that the search for life on exoplanets will be derailed by false-positive biosignatures.

Benoit emphasized that cross-validation with astrochemical models and experimental observations would strengthen the results. For example, the simultaneous detection of carbon dioxide, helium and oxygen on a exoplanet could validate this pathway as an important mechanism for molecular oxygen production.

“This new mechanism will likely be incorporated into future models used to predict the atmospheres of other planets,” Benoit said, “and help us better explain the amounts of oxygen we might find there.”