We just got the most detailed view of an exoplanet atmosphere yet

WASP-39b, a gas giant about 700 light-years away, turns out to be an exoplanetary treasure trove.

Earlier this year, WASP-39b was the subject of the first-ever 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 to date.

The results include information about WASP-39b’s clouds, the first-ever direct detection of photochemistry in an exoplanet atmosphere, and a near-complete inventory of the atmosphere’s chemical content that reveals tantalizing clues about the atmosphere. history of exoplanet formation.

These epic discoveries were published in five articles in Natureand 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 the JWST,” says astrophysicist Laura Kreidberg, director of the Max Planck Institute for Astronomy in Germany.

“We put the telescope through its paces to test performance, and it was nearly perfect – even better than we expected.”

Since the discovery of the first exoplanets in the early 1990s, we have sought to learn more about these worlds orbiting extraterrestrial stars.

But the challenges have been daunting. Exoplanets can be extremely small and extremely distant. We have never even seen most of them: we only know of their existence by 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 a slight attenuation of starlight; periodic dimming events suggest the presence of an orbiting body. We can even tell how big this orbiting body is, based on the dimming and gravitational effects on the star.

And there’s something else we can say, based on the transit data. As starlight passes through the atmosphere of the transiting exoplanet, it changes. Certain wavelengths in the spectrum are attenuated or brightened, depending on how molecules in the atmosphere absorb and re-emit light.

The signal is weak, but with a sufficiently powerful telescope and a stack of transits, the changing characteristics of absorption and emission on the spectrum can be decoded to determine the contents of an exoplanet’s atmosphere.

JWST is the most powerful space telescope ever launched. With three of his four instruments, he obtained detailed infrared spectra of the star WASP-39. The scientists then set to work analyzing the color codes.

First, an inventory of the molecules present in the atmosphere of WASP-39b. In addition to the aforementioned carbon dioxide, the researchers detected water vapor, sodium, and carbon monoxide. There was no detection of methane, implying that WASP-39b’s metallicity is higher than Earth’s.

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 close 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 such as 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 elements and the resulting sulfur is oxidized.

Photon-induced chemical reactions are known as photochemistry and have implications for habitability, the stability of an atmosphere, and the formation of aerosols.

WASP-39b, to be clear, is probably not habitable for life as we know it for a whole host of reasons, including but not limited to its scorching temperature and gas composition, but 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 for the information about atmospheres that JWST was to provide. With the first detailed analysis of the atmosphere of the exoplanet, it seems that the space telescope will keep its promises.

In addition, the teams involved in this research are preparing documentation so that other scientists can apply their techniques to future observations of JWST exoplanets.

We may not detect the signatures of life in an exoplanet atmosphere with JWST – perhaps an even more powerful telescope will be needed to provide this level of fine detail – but with the analysis of WASP-39b , this discovery feels more and more tempting 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 Nature and can be read in preprint here, here, here, here and here.

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