An artist’s impression of the surface of WASP-39b.
Astrophysicists on Earth are no strangers to WASP-39b, an exoplanet orbiting a star about 700 light-years from Earth, though they’ve never actually seen it directly. Now, the Webb Space Telescope has offered fresh insight into this distant world: Its observations have revealed the recipe list for the planet’s toxic atmosphere.
WASP-39b is a gas giant about the mass of Saturn and the size of Jupiter, but it orbits its star at about the same distance as Mercury is from the Sun, making the exoplanet very, very hot. The exoplanet was discovered in 2011; earlier this year, Webb telescope observations revealed carbon dioxide lurking in its atmosphere.
More molecules and chemical compounds have now been indentified, including evidence of water, sulfur dioxide, carbon monoxide, sodium, and potassium. The findings are under review for publication and currently available on the preprint server arXiv.
“This is the first time we have seen concrete evidence of photochemistry — chemical reactions initiated by energetic stellar light — on exoplanets,” said Shang-Min Tsai, a researcher at the University of Oxford lead author of the paper explaining sulfur dioxide’s presence in the planet’s atmosphere, in a European Space Agency release. “I see this as a really promising outlook for advancing our understanding of exoplanet atmospheres with [this mission].”
It’s no small feat to sniff out the chemicals floating in the atmosphere of a distant world. The nearest confirmed exoplanet is 24.9 trillion miles away. Yet Webb managed to spot such infinitesimal molecules in WASP-39b.
Four graphics showing the spectra observed by NIRISS, NIRCam, and two NIRSpec instruments.
Webb observed the planet by waiting for it to transit in front of its host star; when it did, the star’s light illuminated the planet from behind. Webb picked up infrared wavelengths of that light, and scientists can deduce which chemicals are present in the atmosphere based on the wavelengths of light they absorbed.
Webb’s capabilities have broader implications for understanding the diversity of exoplanets in our galaxy, with an eye toward their potential habitability. With its extreme heat and gaseous composition, WASP-39b is certainly not hospitable to any life we know of—but it’s showcasing the kind of molecular-level analysis Webb can apply to distant worlds.
“I am looking forward to seeing what we find in the atmospheres of small, terrestrial planets,” said Mercedes López-Morales, an astronomer at the Center for Astrophysics | Harvard & Smithsonian and a co-author of the recent work, in the ESA release.
The data suggested to the researchers that the chemicals in the planet’s atmosphere may be broken up in clouds, rather than evenly distributed in its atmosphere. And based on the relative abundances of the chemicals in the atmosphere, the researchers think that WASP-39b emerged from a glomming together of planetesimals over time.
While we don’t know where Webb will turn its infrared gaze next, we know that, at some point, more exoplanets will be on the docket. Webb has already investigated the atmospheres of rocky planets in the TRAPPIST-1 system, and may return to the system in due time. You can keep up with Webb’s most recent targets here.
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