New way of detecting oxygen on exoplanets could help find life

The search for oxygen on other planets outside of our solar system, called exoplanets, is thought to be an aid in the search for life outside of Earth. Now, astronomers have developed a new method for detecting oxygen on exoplanets, according to a new study published Monday.

The scientists believe their new method could speed up the quest for life by making it easier to tell if individual exoplanets could host life on their surfaces by peeking into their atmospheres.

For example, if an alien species was searching for life outside of their planet, one of the ways they could tell Earth hosted life is because of the presence of biosignatures, such as oxygen. Individual organisms like plants on Earth produce oxygen through photosynthesis.

The new method will rely on detecting the strong signal created when oxygen molecules collide in the atmospheres of expoplanets. The method will be used by NASA’s James Webb Space Telescope, which will be able to peer into the atmospheres of exoplanets and search for this signal. The telescope will launch in 2021 and take a closer look at intriguing exoplanet targets already identified by previous planet-hunting missions such as NASA’s Kepler and TESS.

This unique signal produced by oxygen molecule collisions could actually help astronomers decide if the planet hosts life or not. Once this determination is made, they could quickly move on in the search.

The details of the new method were published in the journal Nature Astronomy and presented at the 235th meeting of the American Astronomical Society in Honolulu.

“Before our work, oxygen at similar levels as on Earth was thought to be undetectable with Webb,” said Thomas Fauchez, lead study author at NASA’s Goddard Space Flight Center. “This oxygen signal is known since the early 1980s from Earth’s atmospheric studies but has never been studied for exoplanet research.”

The collision of the oxygen molecules is key because they block infrared light from the telescope, creating patterns in the spectrum that help determine the composition of the atmosphere. To create their method, the researchers calculated the amount of light expected to be blocked out by the collisions.

“Oxygen is one of the most exciting molecules to detect because of its link with life, but we don’t know if life is the only cause of oxygen in an atmosphere,” said Edward Schwieterman, study co-author and astrobiologist at the University of California, Riverside. “This technique will allow us to find oxygen in planets both living and dead.”

The presence of oxygen alone in an exoplanet atmosphere is no guarantee that life is present as well. Sometimes oxygen acts like a false positive of a biosignature because it can form in other ways.

Some of the exoplanets discovered in recent years are incredibly close to their host stars. In the 2010s, astronomers found that exoplanets were common around cool, M-dwarf stars which are much dimmer than our sun. This means that exoplanets can be closer to their stars.

Some of these planets, like those in the TRAPPIST system, were found to be potentially habitable — at the right distance from the star to be warm and support liquid water on the surface. But M-dwarfs are also active, meaning the stars can be lashed with intense radiation and light — something Earth doesn’t encounter from the sun.

If liquid water is on the planet’s surface, it will heat up and evaporate, creating the presence of water vapor, broken down into hydrogen and oxygen, in the atmosphere.

Light hydrogen gas leaves the atmosphere and disperses into space. Oxygen, which is heavier, remains behind, making it appear that the planet has an oxygen atmosphere just right for life. In reality, the thick oxygen atmosphere is too great to have been generated by photosynthesis and instead reveals water loss.

This method will help astronomers to understand the difference when they look at exoplanet atmospheres.

“It is important to know whether, and how, much dead planets generate atmospheric oxygen, so that we can better recognize when a planet is alive or not,” Schwieterman said.