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Webb telescope 1st close look at exoplanet atmosphere

Webb telescope: Large planet with banded, cloudy atmosphere and bright sun in distance.
View larger. | Artist’s concept of what WASP-39b might look like. NASA’s Webb telescope has completed the most detailed analysis of this planet’s atmosphere – or any exoplanet – so far. Image via NASA/ ESA/ CSA/ Joseph Olmsted (STScI).

The Webb space telescope just took its first close look at the atmosphere of a distant giant exoplanet, NASA announced on Tuesday, November 22. The new profile of the atmosphere of this distant world reveals atoms, molecules, active chemistry and clouds. The planet WASP-39b is a hot Saturn-sized gas giant that orbits very close to its star. It’s 700 light-years away. While WASP-39b isn’t a habitable world, the results do show the great detail with which Webb will be able to study the atmospheres of many other exoplanets, including potentially habitable rocky ones like Earth.

Researchers working on the WASP-39b data have released five new papers (not yet peer-reviewed) to Nature: L. Alderson et al., Z. Rustamkulov et al., E. Ahrer et al., A. Feinstein et al. and S. Tsai et al. Three of the papers are currently in press and two are under review.

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Webb telescope reveals WASP-39b’s hot atmosphere

Astronomers have studied WASP-39b’s atmosphere before, using the Webb, Hubble and Spitzer space telescopes. The newest analysis from Webb, however, provides far more detail, a full menu of the atmosphere’s ingredients. And, although the planet is too far away to image directly and show any detail, the Webb analysis even hints at what its clouds look like. Indeed, the data suggests the clouds are broken up, rather than being a uniform cloud layer.

In fact, Webb’s sophisticated instruments are able to study exoplanet atmospheres in much greater detail than ever before.

Natalie Batalha, an astronomer at the University of California, Santa Cruz, is a co-author on all five papers and helped coordinate the research. She said:

We observed the exoplanet with multiple instruments that, together, provide a broad swath of the infrared spectrum and a panoply of chemical fingerprints inaccessible until [this mission]. Data like these are a game changer.

New revelations

The molecular and chemical profile of WASP-39b unveils the planet’s atmosphere in unprecedented detail. This includes the first detection of sulfur dioxide in the atmosphere of an exoplanet. Chemical reactions create the sulfur dioxide, a result of intense radiation from the star hitting the planet’s atmosphere. The radiation is strong indeed, since the planet orbits eight times closer to its star than Mercury orbits our sun. This process is, notably, also similar to how the Earth’s ozone layer is created.

Now, thanks to Webb, photochemistry astronomers have confirmed photochemistry on an exoplanet for the first time. As Shang-Min Tsai at the University of Oxford in the U.K. and lead author of the fifth paper stated:

This is the first time we see concrete evidence of photochemistry – chemical reactions initiated by energetic stellar light – on exoplanets. I see this as a really promising outlook for advancing our understanding of exoplanet atmospheres with [this mission].

With this in mind, being able to analyze photochemistry will help astronomers find and interpret potential evidence of habitability on some other exoplanets later on. As Batalha noted:

Planets are sculpted and transformed by orbiting within the radiation bath of the host star. On Earth, those transformations allow life to thrive.

In addition, Webb also detected carbon dioxide, carbon monoxide, sodium, potassium and water vapor in WASP-39b’s atmosphere. No methane or hydrogen sulfide were found, however. Hence, if they are there, they must be at levels too low for even Webb to detect.

4 rectangular graphs with text annotations and planet behind them.
View larger. | Atmospheric composition of WASP-39b. Webb has found sulfur dioxide, carbon dioxide, carbon monoxide, sodium, potassium and water vapor in the planet’s hot atmosphere. Image via NASA/ ESA/ CSA/ Joseph Olmsted (STScI).

WASP-39b in transit

So, just how did Webb observe WASP-39b’s atmosphere? It did so by watching the planet as it transited in front of its star. This is known as the transit method for detecting and studying exoplanets. As the planet transited, the light from the star filtered through the atmosphere. Webb observes the universe in ultraviolet light. So, the astronomers looked at the colors in the starlight spectrum. Different chemicals absorb different colors. With this in mind, the astronomers examined which colors were missing from the spectrum to determine what molecules are in WASP-39b’s atmosphere.

Ultimately, hundreds of researchers from around the world analyzed the data from Webb. And indeed, the results were extraordinary; as Hannah Wakeford, an astrophysicist at the University of Bristol in the U.K., said:

We had predicted what [the telescope] would show us, but it was more precise, more diverse and more beautiful than I actually believed it would be.

The results also support the scientific theory that planets first start to form as smaller planetesimals. These smaller bodies collide in the early history of a solar system, gradually creating larger planets. As Kazumasa Ohno at UC Santa Cruz noted:

The abundance of sulfur [relative to] hydrogen indicated that the planet presumably experienced significant accretion of planetesimals that can deliver [these ingredients] to the atmosphere. The data also indicates that the oxygen is a lot more abundant than the carbon in the atmosphere. This potentially indicates that WASP-39 b originally formed far away from the central star.

Searching for habitable worlds with the Webb telescope

These are exciting results, not only for the study of WASP-39b, but for learning more about exoplanets in general. In particular, the search is on for planets that are potentially habitable. Some of the other planets that Webb is, and will be, looking at are rocky worlds more like Earth, Mars or Venus. Webb will be able to examine those planets’ atmospheres as well.

The TRAPPIST-1 system is of special interest, with no less than seven Earth-sized planets. Three of those planets are in the star’s habitable zone, where temperatures could allow liquid water to exist. Webb has already looked at some of these worlds, with more observations planned. No results have been published yet, but they should certainly be interesting when they are!

This is indeed an exciting time for exoplanet science. Team member Laura Flagg, a researcher at Cornell University, said:

We are going to be able to see the big picture of exoplanet atmospheres. It is incredibly exciting to know that everything is going to be rewritten. That is one of the best parts of being a scientist.

Bottom line: For the 1st time, the new Webb telescope has analyzed the atmosphere of an exoplanet orbiting a distant star. It probed the atmosphere of Saturn-sized WASP-39b in fantastic detail. Read about this dazzling new work by Webb.

Sources (preprint):

(1) Early Release Science of the Exoplanet WASP-39b with JWST NIRSpec G395H

(2) Early Release Science of the exoplanet WASP-39b with JWST NIRSpec PRISM

(3) Early Release Science of the exoplanet WASP-39b with JWST NIRCam

(4) Early Release Science of the exoplanet WASP-39b with JWST NIRISS

(5) Direct Evidence of Photochemistry in an Exoplanet Atmosphere

Via Webb Space Telescope


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