Atmospheric oxygen isn’t proof of life on exoplanets

New Scientist : As the search for exoplanets continues, and techniques and equipment improve, work is being done to chemically analyze the atmospheres of detected planets. Research and theory had suggested that a planet that lies within its star’s habitable zone and has an oxygen-rich atmosphere must support life: It was thought that living organisms were necessary to replenish the oxygen gas, which reacts easily with other materials to form various chemicals. Now, Robin Wordsworth at the University of Chicago has shown that nonbiological processes could also produce oxygen-rich atmospheres. On a watery world, UV light from the planet’s star can break down the H₂O molecules, and the hydrogen gas could escape the atmosphere. A similar process could transpire on a rocky planet if it had low levels of argon and nitrogen in its atmosphere, which would allow water to vaporize more easily. Wordsworth’s work means that remote detection of an oxygen-rich atmosphere will not be enough to assume an exoplanet supports life.