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Yes, exoplanets can have oxygen without alien life

The discovery of life on another world would be a monumental moment in the history of human civilization. The most likely way we will, one day, find alien life will be discovering chemical markers of life in the atmosphere of planets orbiting distant stars.

One of these markers is oxygen, which currently makes up a little over 20 percent of the atmosphere of our own world. However, our own world held onto relatively little oxygen until 2.4 billion years ago, when oxygen-producing cyanobacteria filled the atmosphere with the gas, leading to the first widespread extinction — the Great Oxidation event. Many lifeforms on Earth today, including human beings, are now dependent on this life-giving gas.

“Oxygen is a promising exoplanet biosignature due to the evolutionary advantage conferred by harnessing starlight for photosynthesis, and the apparent low likelihood of maintaining oxygen‐rich atmospheres without life,” researchers explained in an article published in the journal AGU Advances.

Ollie ollie exoplanet!

There are three scenarios through which we might discover life. The first of these, and the least likely, is the arrival on our planet of members of an intelligent civilization in spacecraft. The second means of finding life would be the detection of an intelligent signal from another world, most likely through radio waves. The most-likely scenario would be the discovery of gases, like large quantities of oxygen, methane, or phosphine, in the atmosphere of an alien world.

The James Webb Space Telescope should soon become the latest planet hunter in the search for exoplanets — some of which might be home to life. We talk with Scott Lambros, NASA’s instrument systems manager on this revolutionary observatory in space.

A new study from researchers at UC Santa Cruz highlights the need for an array of next-generation telescopes capable of searching exoplanets for multiple, independent, signs of life.

“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. For each scenario, we try to say what your telescope would need to be able to do to distinguish this from biological oxygen,” Joshua Krissansen-Totton, a Sagan Fellow in the Department of Astronomy and Astrophysics at UC Santa Cruz, explains.

Researchers hope that in the next 15 years or so, one or more telescopes in space will be capable of directly imaging exoplanets orbiting other stars, and studying the chemical makeup of their atmospheres. Such study could provide multiple means to detect life on other worlds, providing additional evidence for the discovery.

“There has a been a lot of discussion about whether detection of oxygen is ‘enough’ of a sign of life. 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?” Jonathan Fortney, professor of astronomy and astrophysics at UCSC stated.

Credit: J. Krissansen-Totton