One of the amazing abilities of the James Webb Space Telescope is not just detecting the presence of far-off planets, but also being able to peer into their atmospheres to see what they are composed of. With previous telescopes, this was extremely difficult to do because they lacked the powerful instruments needed for this kind of analysis, but scientists using Webb recently announced they had made a rare detection of methane in an exoplanet atmosphere.
Scientists studied the planet WASP-80 b using Webb’s NIRCam instrument, which is best known as a camera but also has a slitless spectroscopy mode which allows it to split incoming light into different wavelengths. By looking at which wavelengths are missing because they have been absorbed by the target, researchers can tell what an object — in this case, a planetary atmosphere — is composed of.
Even with Webb’s sensitive instruments, it’s still difficult to detect an exoplanet though. That’s because planets are so much smaller and dimmer than stars, which makes them almost impossible to view directly. Instead, researchers often detect them by observing the stars around which they orbit, using techniques like the transit method which measures the dip in a star’s brightness that occurs when a planet moves in front of it.
“Using the transit method, we observed the system when the planet moved in front of its star from our perspective, causing the starlight we see to dim a bit,” one of the study’s authors, Luis Welbanks of Arizona State University, explained in a statement. “It’s kind of like when someone passes in front of a lamp and the light dims. During this time, a thin ring of the planet’s atmosphere around the planet’s day/night boundary is lit up by the star, and at certain colors of light where the molecules in the planet’s atmosphere absorb light, the atmosphere looks thicker and blocks more starlight, causing a deeper dimming compared (with) other wavelengths where the atmosphere appears transparent. This method helps scientists like us understand what the planet’s atmosphere is made of by seeing which colors of light are being blocked.”
When the authors used this method on WASP-80b, they found evidence of both water and methane in the planet’s atmosphere. Planets in our solar system like Jupiter and Saturn have methane in their atmospheres too, but this planet is much warmer, with a temperature of over 1,000 degrees Fahrenheit. Finding methane in a planet of this type, called a warm Jupiter, is exciting because it can help scientists learn about planetary atmospheres and also because despite it being commonly found in planetary atmospheres in our solar system, it is rarely detected in exoplanet atmospheres.
It could also be relevant for the hunt for life beyond our planet. “Not only is methane an important gas in tracing atmospheric composition and chemistry in giant planets, it is also hypothesized to be, in combination with oxygen, a possible signature of biology,” Wellbanks said. “One of the key goals of the Habitable Worlds Observatory, the next NASA flagship mission after JWST and Roman, is to look for gases like oxygen and methane in Earth-like planets around sun-like stars.”
The research is published in the journal Nature.
