New Technique Uses Oxygen Signal to Look for Life on Exoplanets

A new technique has been created by researchers to detect oxygen in the atmospheres of exoplanets. This technique could speed up the search for life on exoplanets.

Conceptual image of water-bearing (left) and dry (right) exoplanets with oxygen-rich atmospheres. The red sphere is the M-dwarf star around which the exoplanets orbit. The dry exoplanet is closer to the star, so the star appears larger. Image Credit: NASA/GSFC/Friedlander-Griswold.

The presence of oxygen in the atmosphere of an exoplanet is a possible sign of life or biosignature. On Earth, living organisms like cyanobacteria, algae, and plants synthesize oxygen during photosynthesis, involving converting sunlight into chemical energy.

The new UC Riverside-led study has resulted in a new method, which employs NASA’s James Webb Space Telescope to track a strong signal produced by oxygen molecules upon collision. Researchers can then use this signal to differentiate between nonliving and living planets.

The fact that exoplanets orbiting stars other than the sun are very distant, makes it impossible for researchers to visit these faraway worlds and look for signs of life. Rather, it is necessary to make use of an advanced telescope, such as the Webb, to observe what exists inside the exoplanets’ atmospheres.

Before our work, oxygen at similar levels as on Earth was thought to be undetectable with Webb. This oxygen signal is known since the early 1980s from Earth’s atmospheric studies but has never been studied for exoplanet research.

Thomas Fauchez, Study Lead Author, Goddard Space Flight Center, NASA

Edward Schwieterman, an astrobiologist at UC Riverside, originally put forward an analogous method detecting high oxygen concentrations arising from nonliving processes. He was a member of the group that created this method. The study was recently reported in the Nature Astronomy journal.

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. This technique will allow us to find oxygen in planets both living and dead.

Edward Schwieterman, Astrobiologist, University of California, Riverside

Upon collision, oxygen molecules block portions of the infrared light spectrum from being observed by a telescope. Analysis of patterns in this light will help to determine the composition of the planet's atmosphere. Schwieterman assisted the NASA group in computing the amount of light that would be blocked by these oxygen collisions.

Surprisingly, certain scientists suggest oxygen can also show an exoplanet appearing to host life when it does not. This is due to the pile-up in the atmosphere of a planet, even without any life activity.

The extremely close proximity of an exoplanet to its host star or receiving too much starlight can lead to the atmosphere turning warm, saturated with water vapor arising from evaporating oceans. Subsequently, this water could be disintegrated by powerful ultraviolet radiation into atomic hydrogen and oxygen. Since hydrogen is a light atom, it easily escapes to space, where the oxygen is left behind.

Gradually, this process may lead to loss of entire oceans while amassing a thick oxygen atmosphere—even more, than could be produced by life. Therefore, copious oxygen in the atmosphere of an exoplanet may not inevitably mean abundant life, but rather point towards a water loss history. Schwieterman warns that astronomers are still unsure of how prevalent this process could be on exoplanets.

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.

Edward Schwieterman, Astrobiologist, University of California, Riverside

Schwieterman, who is a visiting postdoctoral fellow at UC Riverside, will soon start working as an assistant professor of astrobiology in the Department of Earth and Planetary Sciences.

The study was funded by Goddard’s Sellers Exoplanet Environments Collaboration, which is partially supported by the NASA Planetary Science Division’s Internal Scientist Funding Model. The research was also funded by the European Union’s Horizon 2020 research and innovation program under the Marie Sklodowska-Curie Grant, the NASA Astrobiology Institute Alternative Earths team, and the NExSS Virtual Planetary Laboratory.

Upon being launched in 2021, Webb will be the foremost space science observatory in the world. It will enable researchers to solve mysteries in the solar system, explore distant worlds around other stars, and investigate the mysterious structures and origins of the universe and Earth’s place in it.

Bill Steigerwald and Nancy Jones from the NASA Goddard Space Flight Center contributed significantly to this study.


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