WASP-39b, a gas giant about 700 light-years away, is turning out to be quite an exoplanetary treasure trove.
Earlier this year, WASP-39b was the subject of the first detection of carbon dioxide in the atmosphere of a planet outside the Solar System.
Now, an in-depth analysis of data from the James Webb Space Telescope (JWST) has given us an absolute goldmine of information: the most detailed look at an exoplanet’s atmosphere yet.
The results include information about the clouds of WASP-39b, the first direct detection of photochemistry in an exoplanet atmosphere, and a near-complete inventory of the atmosphere’s chemical content that reveals tantalizing hints of the formation history of the exoplanet
These epic discoveries have been published in five papers in Nature and pave the way for the eventual detection of the chemical signatures of life outside the Solar System.
“These early observations are a harbinger of more amazing science to come with JWST,” says astrophysicist Laura Kreidberg, director of the Max Planck Institute for Astronomy in Germany.
“We put the telescope to the test to test the performance, and it was almost flawless, even better than we expected.”
Ever since the first exoplanets were discovered in the early 1990s, we’ve sought to learn more about these worlds orbiting alien stars.
But the challenges have been strong. Exoplanets can be extremely small and extremely distant. We haven’t even seen most of them: we only know of their existence from the effect they have on their host stars.
One such effect occurs when the exoplanet passes between us and the star, an event known as a transit. This causes the starlight to dim slightly; periodic dimming events suggest the presence of an orbiting body. We can even tell the size of this orbiting body, based on the attenuation and gravitational effects on the star.
And there’s something else we can tell, based on traffic data. As the starlight passes through the atmosphere of the transiting exoplanet, it changes. Certain wavelengths of the spectrum are dimmed or brightened, depending on how the molecules in the atmosphere absorb and re-emit the light.
The signal is weak, but with a powerful enough telescope and a stack of transits, the changing absorption and emission features of the spectrum can be decoded to determine the content of an exoplanet’s atmosphere.
JWST is the most powerful space telescope ever launched. With three of its four instruments, it obtained detailed infrared spectra of the star WASP-39. The scientists then got to work analyzing the color codes.
First was a census of the molecules present in WASP-39b’s atmosphere. In addition to the aforementioned carbon dioxide, the researchers detected water vapor, sodium and carbon monoxide. There was no detection of methane, implying that the metallicity of WASP-39b is higher than that of Earth.
The abundance of these elements is also revealing. In particular, the carbon-to-oxygen ratio suggests that the exoplanet formed much farther from its host star than its current nearby position, occupying a four-day orbit. And modeling and observational data suggest that the exoplanet’s sky is populated by broken clouds, not water, but silicates and sulfites.
Finally, the observations revealed the presence of a compound called sulfur dioxide. Here in the Solar System, on rocky worlds like Venus and the Jovian moon Io, sulfur dioxide is the result of volcanic activity. But on gaseous worlds, sulfur dioxide has a different origin story: it is produced when hydrogen sulfide is broken down by light into its constituent parts and the resulting sulfur is oxidized.
Photon-induced chemical reactions are known as photochemistry and have implications for habitability, atmospheric stability, and aerosol formation.
WASP-39b, to be clear, is unlikely to be habitable for life as we know it for a host of reasons, including but not limited to its scorching temperature and gaseous composition, but the detection of photochemistry is one that has implications for atmospheric studies of other worlds and understanding the evolution of WASP-39b itself.
Planetary scientists have been preparing for years to learn about the atmospheres that JWST was expected to provide. With the first detailed analysis of an exoplanet’s atmosphere, the space telescope looks set to deliver on its promise.
In addition, the teams involved in this research are preparing documentation so that other scientists can apply their techniques to future JWST observations of exoplanets.
We may not detect the signatures of life in an exoplanet atmosphere with JWST (an even more powerful telescope may be needed to provide this level of detail), but with the analysis of WASP-39b, this discovery is felt every time more attractive at hand. .
“Data like this,” says astronomer Natalie Batalha of the University of California, Santa Cruz, “is a game changer.”
The research will be published in Nature and can be read in preprints here, here, here, here and here.