Headline:
Scientists Discover Novel Mechanism for Oxygen Formation in CO2-Rich Atmospheres
Subhead:
New finding challenges assumptions about life detection on exoplanets and Earth’s oxygen origin
Article:
In a groundbreaking discovery, scientists have appena found a new pathway for the formation of oxygen in atmospheres rich in carbon dioxide (CO2), challenging our understanding of how to search for life on other planets and potentially shedding light on Earth’s own oxygen origins.
David Benoit, a senior lecturer in Molecular Physics and Astrochemistry at the University of Hull, not involved in the study, told Space.com, "Most searches for life, or signs of life, on other planets essentially show that what we’re observing can be produced through processes that don’t require life." This study, however, presents an alternative route for producing molecular oxygen that hadn’t been considered before.
Before the Great Oxygenation Event around 2.4 billion years ago, Earth’s primordial atmosphere was dominated by CO2 with only trace amounts of oxygen (O2). Until now, it was believed that molecular O2 was exclusively produced through abiotic (non-biological) processes such as three-body recombination of oxygen atoms or CO2 dissociation under UV light, or specific reactions with electrons.
However, a team led by Shan Xi Tian and Jie Hu from the University of Science and Technology of China has discovered a entirely different pathway for generating O2 from CO2 moleculars: through a reaction with helium ions (He+). This occurs when particles called alphas in the solar wind interact with atmospheric molecules, creating charged particles known as ions that can then react with CO2 to form O2.
While these reactions have been proven to produce various ions like O+, O2+, and CO2+ in Mars’ ionosphere, there’s still no evidence that O2 is formed this way. To confirm their theory, the scientists used time-of-flight (TOF) mass spectrometry, a technique that identifies the mass-to-charge ratio of gas-phase ions by measuring the time they take to travel a known distance in a device called a mass spectrometer.
The team took this further by combining TOF with a device called a ‘crossing beam’ and an ‘ion map’ to visualize any mechanisms that could produce oxygen molecules. In this set-up, two particle beams – CO2 and He+ – collide under controlled conditions, allowing reactions to occur at the point of impact. The resulting products are ionized, and their mass-to-charge ratios are determined by the time taken to reach the detector. Simultaneously, ion mapping tracks the trajectory and speed of the ions, providing detailed energy information.
By reconstructing the reaction pathway and gaining crucial insights into the step-by-step process of O2 formation from these two initial materials, the team successfully demonstrated that collisions between helium and CO2 at energies observed in the solar wind can indeed produce molecular oxygen.
"Our findings show that the collision of helium at energies we observe in the solar wind, can produce molecular oxygen when it interacts with carbon dioxide," said Benoit. "The efficiency of this process appears to be similar to collisions between carbon dioxide and low-energy electrons, studied by the same research group a few years ago."
Since life on Earth is strongly tied to oxygen concentrations, scientists have long studied atmospheric oxygen as a potential sign of habitability on other worlds. However, this research suggests that oxygen can also be formed through abiotic processes, meaning it could exist in planets with CO2-rich atmospheres even without life.
But this discovery doesn’t mean astronomers will rush to conclusions or that searches for life on exoplanets will be hindered by false positive biosignatures. Benoit emphasizes that cross-validation with astrochemical models and experimental observations will strengthen these findings. For instance, the simultaneous detection of CO2, helium, and oxygen in an exoplanet could validate this pathway as a significant mechanism for molecular oxygen production.
"It’s likely that this new mechanism will be incorporated into future models used to predict the atmospheres of other planets," concluded Benoit, "and it will help us better explain the amount of oxygen we might find there."
