When astronomers scan the universe for signs of extraterrestrial life, they might be on the lookout for a few things. Water vapor, methane and amino acids are all considered key clues in our ongoing search for life and potentially habitable planets, as is oxygen. Scientists have now come up with a new way of quickly identifying this key element in the atmospheres of distant worlds, with plans to apply the technique to the observations of NASA's James Webb Space Telescope, which is slated to launch next year.
Unlike the nearby planets inhabiting our solar system, scientists are not able to study exoplanets around other stars by observing them directly. This is because the blinding light emanating from the parent star makes them difficult to see in any great detail, leading astronomers to use a technique known as transit spectroscopy instead.
This means studying the atmosphere of the planet, rather than the body itself, as it passes in front of the star. When this happens, the starlight passing through the atmosphere enables scientists to measure things like its temperature and chemical composition, by observing which wavelengths of light make it through and which ones don't.
With its unprecedented light-collecting abilities, the powerful James Webb Space Telescope is already well poised to scan this atmospheric light for signatures of key molecules and atoms. But this new technique, developed by scientists at NASA together with researchers at the University of California, Riverside, is set to add a potent new skill to its repertoire.
“Before our work, oxygen at similar levels as on Earth was thought to be undetectable with Webb,” says Thomas Fauchez of NASA’s Goddard Space Flight Center and lead author of the study. “This oxygen signal is known since the early 1980s from Earth’s atmospheric studies but has never been studied for exoplanet research.”
The team's technique leverages knowledge of the behavior of oxygen molecules as they collide with one another. When these collisions take place, they prevent certain types of infrared light from passing through. Through computer modeling, the scientists calculated how much light would be blocked by these collisions in an exoplanet around an M dwarf star, the most common type found across the universe.
This modeling of atmospheric chemistry offered up a signature the scientists say can quickly reveal the presence of an oxygen-rich atmosphere around an exoplanet.
While this technique might be useful in leading scientists towards exoplanets with some form of life, the detection of oxygen in an atmosphere doesn't offer any guarantees. Oxygen can also build up when an exoplanet orbits close to its parent star and water from its evaporating oceans is broken down into hydrogen and oxygen, the latter of which stays trapped in the atmosphere.
“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,” Fauchez says.
The scientists will put their new oxygen identification technique to use on the James Webb Space Telescope, which is scheduled for launch in March 2021.
The research was published in the journal Nature Astronomy.