New Study Complicates the Search for Alien Oxygen

By Andy Tomaswick - March 17, 2026 01:30 PM UTC | Astrobiology
Artist's depiction of TRAPPIST-1 b. Credit - NASA, ESA, CSA, J. Olmsted (STScI), T. P. Greene (NASA Ames), T. Bell (BAERI), E. Ducrot (CEA), P. Lagage (CEA)
Artist's depiction of TRAPPIST-1 b. Credit - NASA, ESA, CSA, J. Olmsted (STScI), T. P. Greene (NASA Ames), T. Bell (BAERI), E. Ducrot (CEA), P. Lagage (CEA)

Oxygen has been the most important gas in our search for life among the cosmos thus far. On Earth, we have it in abundance because it is produced by biological synthesis. But that might not be the case on other planets, so even if we do find a very clear high oxygen signal in the atmosphere of an exoplanet, it might not be a clear indication that life exists there. A new paper, available in pre-print on arXiv, from Margaret Turcotte Seavey and a team of researchers from institutions like the NASA Goddard Space Flight Center and Johns Hopkins University, adds some additional context to what else might be going on in those atmospheres. In particular, they note that if there’s even a little bit of water vapor, it can make a big difference in whether a lifeless rock looks like a living, thriving world.

Part of their inspiration for this new paper came from a seminal one published back in 2015 by Peter Gao and his colleagues in the Astrophysical Journal. In it, they describe how desiccated planets around M dwarf stars can have extremely high rates of oxygen in their atmosphere - even rivaling Earth's - despite it being created by completely abiotic processes. This is critical for astrobiologists for a few reasons. M dwarfs are the most common types of stars in the galaxy, and also the easiest ones to find exoplanets around. Many of their planets also seem to have largely carbon dioxide atmospheres, which is another critical component in the oxygen production chain.

According to the 2015 paper, intense UV light from the planet’s star can split the carbon dioxide molecules into carbon monoxide and oxygen via a process called photolysis. This process would eventually result in an atmosphere that looks suspiciously like a biological one, but is in fact abiotic in its entirety.

Fraser talks about the physics needed to find Earth in other solar systems.

Then we come to the astrobiologist’s other favorite molecule - water. Ms. Seavey and her team wanted to see what would happen if they ran the same process as the 2015 paper, but included differing levels of water vapor in the atmosphere as well. They used a complex photochemical-climate model called “Atmos” to simulate a rocky, Mars-sized planet with a 1-bar CO2 atmosphere orbiting an M-dwarf star, but varied the amount of water vapor the planet had in its atmosphere.

Across the different water levels they tested, the maximum abundance of oxygen in these scenarios got up to only 2.7% - only about 10% of the level that was reported in the 2015 paper, and, similarly, what is found on Earth. The chemical pathway for this decrease in oxygen is well understood. The same UV light that breaks apart the CO2 molecules also breaks apart water, which creates a free hydrogen and a hydroxyl (OH) radical. These OH radicals act as a catalyst with atomic oxygen and carbon monoxide, reforming it back into CO2, thereby lowering the overall free oxygen levels.

Ultimately, oxygen never gets the chance to accumulate in the atmosphere with this process going on, making a scenario where there is a high percentage of both water vapor and oxygen in the atmosphere more of a “smoking gun” for some sort of biological process rather than an abiotic one. We already have a good model for what that would look like, as Earth itself is a case in point of that.

Anton Petrov explains the implications of oxygen on exoplanets. Credit - Anton Petrov YouTube Channel

As further astrobiological missions, such as the Habitable Worlds Observatory and LIFE telescopes, begin to gain steam, more of these model-based papers describing what scientists think they should look out for become critical. A big takeaway from this one is that we need to look at an exoplanet’s entire atmosphere - understanding whether there is both water vapor and oxygen in an atmosphere will help determine if the world is a desiccated false positive or a potentially lush object of interest. Ultimately work like this brings us a little closer to ensuring that, when we do finally detect life out amongst the cosmos, we can be confident that it’s the real deal.

Learn More:

M. T. Seavey et al. - Oxygenated False Positive Biosignatures in Mars-like Exoplanet Atmospheres

UT - Scientists Discover a New Way Exoplanets Could Make Oxygen; Unfortunately, it Doesn't Require Life

UT - Finding Oxygen on an Alien World Doesn't Always Mean There's Life There

UT - The Combination of Oxygen and Methane Could Reveal the Presence of Life on Another World

Andy Tomaswick

Andy Tomaswick

Andy has been interested in space exploration ever since reading Pale Blue Dot in middle school. An engineer by training, he likes to focus on the practical challenges of space exploration, whether that's getting rid of perchlorates on Mars or making ultra-smooth mirrors to capture ever clearer data. When not writing or engineering things he can be found entertaining his wife, four children, six cats, and two dogs, or running in circles to stay in shape.