James Webb Space Telescope Reveals Alien Planet's Atmosphere Like Never Before

 WASP-39b is now the best-explored planet outside the solar system. 

An artist's depiction of the exoplanet WASP-39b.An artist's depiction of the exoplanet WASP-39b. (Image credit: NASA, ESA, CSA, Joseph Olmsted (STScI))

A boiling Saturn-like planet 700 light-years away from the sun has become the best-explored planet outside our solar system. The James Webb Space Telescope's measurements of the planet's atmosphere have revealed unprecedented details of its chemistry, and even allowed astronomers to test methods for detecting alien life.  

The exoplanet WASP-39b, which orbits a star in the constellation Virgo, made headlines in late August when the James Webb Space Telescope (Webb or JWST) found carbon dioxide in its atmosphere. It was the first ever such detection and experts hailed the finding as a major breakthrough. Now, less than three months later, an avalanche of studies based on the grand telescope's observations have revealed the most minute details of WASP-39b's atmosphere, which even enabled astronomers to make conclusions about the exoplanet's formation history.  

"These early observations are a harbinger of more amazing science to come with JWST," Laura Kreidberg, director of the Max Planck Institute for Astronomy (MPIA) in Germany who was involved in the observations, said in a statement. "We put the telescope through its paces to test the performance, and it was nearly flawless — even better than we hoped." 

Astronomers used three out of Webb's four instruments to observe the distant planet: the main NIRCam camera and the two spectroscopes NIRISS and NIRSpec, which split light from the observed objects into light spectra, the barcode-like fingerprints that reveal the chemical compositions of the observed planets and stars.  

The observations revealed that WASP-39b is shrouded in thick clouds containing sulfur and silicates. These chemicals interact with the light of the parent star, producing sulfur dioxide in a reaction similar to the one that produces ozone in Earth's atmosphere 

WASP-39b is a gas giant about one-third the size of the solar system's largest planet, Jupiter, and orbits only 4.3 million miles (7 million kilometers) away from its parent star, or eight times closer than the distance of the solar system's innermost planet Mercury from the sun.  

The sheer intensity of starlight that batters WASP-39b makes the planet an ideal laboratory for studying such photochemical reactions, scientists said in the statement. 


The level of detail provided by JWST allowed astronomers to peek into WASP-39b's past and learn how this hot and scorching world came into being. From the ratios of carbon to oxygen, of potassium to oxygen, and of sulfur to hydrogen in the planet's atmosphere, the researchers inferred that the gas giant planet must have formed from collisions of several smaller planetesimals. In addition, the much higher abundance of oxygen compared to carbon in the thick clouds revealed that WASP-39b formed much farther away from its star than it orbits today.  

"Data like these are a game changer," Natalia Batalha, a professor of astronomy and astrophysics at the University of California at Santa Cruz who coordinated the observing program, said in the statement. 

The observations even allowed astronomers to test methods that one day could help detect life on other exoplanets. That detection would rely on a similar atmospheric analysis as conducted on WASP-39b, then compare the results with models of alien planets. If the planet displays more oxygen than those models predict, for example, it could be a sign of life. 

WASP-39b, however, due to its proximity to its parent star, is an improbable candidate to host extraterrestrial life as temperature on the planet soars to an unlivable 1,650 degrees Fahrenheit (900 degrees Celsius).  

Five new studies (1,2,3,4,5) based on JWST data are under review or in press with the journal Nature. 

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