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

We just got the most detailed view of an exoplanet's atmosphere yet
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WASP-39b, a gas giant some 700 light-years away, is turning into quite the 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 gold mine of information: the most detailed look into an exoplanet’s atmosphere yet.

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

These epic discoveries have been published in five articles in Natureand pave the way for the eventual detection of chemical signatures of life outside the Solar System.

“These first observations are a harbinger of the more amazing science to come with JWST,” says astrophysicist Laura KreidbergDirector of the Max Planck Institute for Astronomy in Germany.

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

Ever since the first exoplanets were discovered in the early 1990s, we have sought to learn more about these worlds orbiting alien stars.

But the challenges have been steep. Exoplanets can be extremely small and extremely distant. We haven’t even seen most of them: we only know of their existence based on the effect they have on their host stars.

One of these effects 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 how big that orbiting body is, based on gravitational and dimming effects on the star.

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

The signal is weak, but with a powerful enough telescope and a stack of transits, the changing absorption and emission features in the spectrum can be decoded to determine the content of an exoplanet’s atmosphere.

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

First was a census of the molecules present in WASP-39b’s atmosphere. In addition to the mentioned carbon dioxide, the researchers detected water vapor, sodium and carbon monoxide. No methane was detected, implying that WASP-39b’s metallicity is higher than that of Earth.

The abundance of these elements is also revealing. In particular, the ratio of carbon to oxygen suggests that the exoplanet formed much further from its host star than its present nearby position, occupying a four-day orbit. And modeling and observational data suggest that the exoplanet’s sky is populated by broken clouds, not of water, but of 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 jovian moon me, sulfur dioxide is the result of volcanic activity. But on gaseous worlds, sulfur dioxide has a different origin story: It is produced when light breaks hydrogen sulfide into its constituent parts, and the resulting sulfur is oxidized.

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

WASP-39b, to be clear, isn’t likely to be habitable for life as we know it for a host of reasons, including but not limited to its blistering temperature and gaseous composition, but the photochemical detection has implications for studies. atmospheres from other worlds and understanding the evolution of WASP-39b itself.

Planetary scientists have been preparing for years to learn about the atmospheres the JWST was expected to provide. With the first detailed analysis of the exoplanet atmosphere, it looks like the space telescope is going 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’s atmosphere with JWST (perhaps an even more powerful telescope is required to provide that level of fine detail), but with the analysis of WASP-39b, that discovery is felt every time. more tempting within reach. .

“Data like these” says astronomer Natalie Batalha from the University of California Santa Cruz, “are a game changer.”

The research will be published. Nature and can be read in preprints here, here, here, hereY here.

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