Does the presence of oxygen mean the existence of life? That’s a question that scientists have been debating over recent years as technology and missions into outer space advance and sustain interest in the oft-contemplated question of life outside of Earth. However, new research suggests that the mere presence of oxygen in a planet’s atmosphere doesn’t necessarily equate to extraterrestrial life.
The study, published in AGU Advances, details the possibility of distinct scenarios where oxygen could exist on a lifeless planet. The paper’s authors point toward the need to differentiate between these false positives and make the case for next-generation telescopes that could provide multiple lines of evidence for life other than just the presence of oxygen.
"This is useful because it shows there are ways to get oxygen in the atmosphere without life, but there are other observations you can make to help distinguish these false positives from the real deal," said first author Joshua Krissansen-Totton, who is a Sagan Fellow in the Department of Astronomy and Astrophysics at UC Santa Cruz. "For each scenario, we try to say what your telescope would need to be able to do to distinguish this from biological oxygen."
Coauthor Jonathan Fortney, professor of astronomy and astrophysics and director of UCSC's Other Worlds Laboratory, says that he hopes the paper will act as a call to increase investment in telescopes that could explore Earth-like planets.
"There has been a lot of discussion about whether detection of oxygen is 'enough' of a sign of life," he said. "This work really argues for needing to know the context of your detection. What other molecules are found in addition to oxygen, or not found, and what does that tell you about the planet's evolution?" In order to answer these questions, a telescope must be sensitive enough to measure the properties of the molecules within an exoplanet’s atmosphere. Currently, such a telescope does not exist.
In their computations, the researchers simulated multiple scenarios of rocky planets orbiting Sun-like stars. They showed how oxygen could evolve in the atmospheres of these planets under different situations, demonstrating several that produced oxygen but without the evolution of life. Unlike past studies that have run similar computational models, this study concentrated on the geochemical and thermal evolution of the planet's mantle and crust and the interactions between the crust and atmosphere, instead of the atmospheric processes that would occur.