New JWST data reveal more details of exoplanet WASP-39b's atmosphere

New JWST data reveal more details of exoplanet WASP-39b’s atmosphere

New results from the JWST Transiting Exoplanet team reveal a complete menu of the atoms and molecules that make up exoplanet WASP-39b’s atmosphere, including the first photochemical byproduct detected on an exoplanet.

Among the first results of James Webb Space Telescope (JWST) observations of WASP-39b, reported in August, were the first clear evidence of carbon dioxide in an exoplanet’s atmosphere. At the time, the team noticed an interesting feature in their results, but had not yet identified the molecule responsible.

Now they have identified the “mysterious molecule” as sulfur dioxide and found that it is produced by photochemistry – chemical reactions in the atmosphere driven by light from the planet’s parent star, similar to how ozone is formed by photochemical reactions in Earth’s atmosphere.

“The discovery of photochemistry in the atmosphere of a ‘hot Jupiter’ exoplanet like WASP-39b is important as it allows us to test our photochemical models and open up new avenues of study,” said Natalie Batalha, Professor of Astronomy and Astrophysics at UC Santa Cruz, who leads the JWST Transiting Exoplanet Early Release Science Team.

The team reported their latest findings in a series of five new articles, three of which are in press and two under review. They observed the planet as it passed in front of its host star, allowing them to analyze the starlight transmitted through the planet’s atmosphere, spectroscopically breaking the light down into its wavelengths and revealing the “fingerprints” of the molecules that make up the des Planets are made up of atmospheres.

“We see a variety of atoms and molecules in WASP-39b’s atmosphere, including sodium, potassium, water, carbon dioxide, carbon monoxide, and the mysterious molecule sulfur dioxide,” Batalha said. “The process used to identify molecules also gives us information about the abundance ratios of elements — like carbon to oxygen and potassium to oxygen ratios — which are traces of planet-forming processes.”

The chemical inventory of WASP-39b suggests a history of smashing and merging of smaller bodies called planetesimals to eventually create a Goliath of a planet.

“The abundance of sulphur [relative to] Hydrogen indicated that the planet may have experienced a significant accumulation of planetesimals that can provide [these ingredients] into the atmosphere,” said Kazumasa Ohno, a postdoctoral fellow at UC Santa Cruz who worked on the Webb data. “The data also show that oxygen is much more abundant in the atmosphere than carbon. This may indicate that WASP-39 b originally formed far from the host star.”

The results also showed evidence of patchy clouds in the exoplanet’s atmosphere.

WASP-39b is a hot Saturn-mass gas giant orbiting very closely to its parent star. Its narrow orbit and high temperature are typical of the abundant Hot Jupiter class of exoplanets. The planet’s proximity to its parent star – eight times closer than Mercury is to our Sun – makes it a laboratory for studying the effects of parent star radiation on exoplanets. A better knowledge of the star-planet connection should bring a deeper understanding of how these processes produce the diversity of planets observed in the galaxy.

The team obtained transmission spectra during four transits of WASP-39b using three different instruments on JWST: NIRSpec (in two different observation modes), NIRISS and NIRCam. This yielded transmission spectroscopy data covering the infrared wavelengths from 1 to 5 microns.

“The wide wavelength coverage provides a more complete picture of conditions in the atmosphere,” Batalha said. “In addition, each transit observation provides a planetary spectrum at different but overlapping wavelengths, allowing us to test the reproducibility of each instrument.”

The spectra from different instruments were consistent in the overlapping areas. All instruments met or exceeded expectations, which is good news for astronomers planning future observations. This includes studying the atmospheres of smaller rocky planets like those in the TRAPPIST-1 system.

The following articles from the JWST Transiting Exoplanets Early Release Science Program are currently available online:

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