James Webb Space Telescope Observes Methane in Exoplanet’s Atmosphere


In our atmosphere, there is a tendency, especially in these times of anthropogenic climate warming, to desire the disappearance of methane. a potent greenhouse gas. Conversely, in the atmospheres of exoplanets, astronomers are excited to find methane because it opens up many prospects.

In the constellation of the Eagle, over 160 light-years away from our Earth, there is an exoplanet astronomer called WASP-80b—a hot Jupiter, they say. It has approximately the size and mass of Jupiter but a temperature over four times higher. This hot Jupiter has recently become the subject of a rare discovery. Using the keen eye of the James Webb Space Telescope, NASA astronomers have indeed detected methane (CH4) in its atmosphere. They detail their findings in the journal Nature.

Methane exists in the Earth’s atmosphere; it is a greenhouse gas. However, it is also abundant in the atmospheres of Jupiter, Saturn, Uranus, and Neptune, the giant planets in our Solar System. Detecting this molecule by spectroscopy in the atmospheres of transiting exoplanets has proven challenging for researchers.

Transit and Eclipse Reveal the Exoplanet’s Atmosphere

To clarify, the transit method involves studying the composition of an exoplanet’s atmosphere when the planet passes in front of its star relative to its Earth observer. The star shines during this event, illuminating a thin ring of the atmosphere. The molecules present absorb certain wavelengths, making the atmosphere more opaque for those specific colors.

To complement this data, astronomers employed the eclipse method. They observed the planet passing behind its star. As all objects emit thermal radiation—infrared radiation, to be precise—the intensity and color of this radiation depend on the object’s emitted heat. When the eclipse occurs, the brightness changes. Then, astronomers can gauge the exoplanet’s infrared light output. The molecules in its atmosphere leave absorption traces, typically appearing as decreases in light intensity.

The Certainty of Methane Detection

To transform the raw data into useful spectra, NASA astronomers used two different approaches. They interpreted these results using two types of models, both leading to the same conclusion: the atmosphere of WASP-80b contains methane. According to the researchers, there are almost one in a billion chances that they have made an error. And then?

Understanding the Exoplanet Better With Methane

Researchers first explain that detecting methane in the atmosphere of WASP-80b will help them understand where the exoplanet originated and how it has evolved. The measurement of methane and water on the planet also provides the carbon-to-oxygen atom ratio. This ratio is known to change depending on where and when planets form within their system. Thus, examining this carbon-to-oxygen ratio can offer clues about whether WASP-80b formed near its star or farther away before gradually moving inward. Today, it is so close to its star that it completes an orbit in just three days!

Astronomers are also enthusiastic about the prospect of using this method to compare giant exoplanets with the giant planets in our Solar System, identifying similarities and differences.

Scientists already dream of other discoveries they could make using the James Webb Space Telescope. They hope to probe the atmosphere of WASP-80b at different wavelengths, with the anticipation of discovering other carbon-rich molecules such as carbon monoxide (CO) or carbon dioxide (CO2).