Astronomers sniff out pungent exoplanet using James Webb Space Telescope

ASU scientists contribute to study providing insights into composition of exoplanetary atmospheres

Planet next to a fiery mass.

Exoplanet HD 189733 b, a Jupiter-sized gas giant. Image courtesy Roberto Molar Candanosa/Johns Hopkins University


An exoplanet located a mere 64 light-years away, with a reputation for its extreme weather conditions, is now known for something else a distinctive rotten-egg odor.

A team of astronomers has used data from the James Webb Space Telescope (JWST) to uncover a surprising aspect of the Jupiter-sized gas giant HD 189733 b: It has an atmosphere rich in hydrogen sulfide. 

The detailed study, which was published in Nature, provides researchers with insights into the composition of exoplanetary atmospheres. It was led by Guangwei Fu of Johns Hopkins University and includes Arizona State University co-authors Luis Welbanks, Presidential Postdoctoral Fellow and 51 Pegasi b Fellow, and Michael Line, associate professor, both of the School of Earth and Space Exploration

“HD 189733 b is a giant literally and figuratively in the field," Welbanks said. "It is one of the first hot Jupiters ever discovered and has been the subject of constant research for the last two decades. Having the opportunity to finally study it with our best space telescope yet is exhilarating.”

The planet, which is unlike anything in our solar system, continues to fascinate scientists. It has an orbit lasting only about two Earth days, and temperatures soaring to 1,700 degrees Fahrenheit. The team studied this canonical hot Jupiter with JWST and found that it has an atmosphere predominantly made of hydrogen sulfide, a molecule that not only gives off a stench but also offers scientists new clues about how sulfur, a building block of planets, might influence the insides and atmospheres of gas worlds beyond the solar system.

“(This discovery) is an important contribution to our understanding of the major elemental reservoirs in exoplanet atmospheres,” Line said.

In addition to detecting hydrogen sulfide, the team analyzed the planet's oxygen and carbon content, pinpointing water, carbon dioxide and carbon monoxide as major components of the planetary atmosphere. Measuring these heavy elements allows astronomers to compare the composition of exoplanets to that of gas giants in our solar system like Jupiter and Uranus. 

“One of the big questions in our field is trying to understand how planets form, and we try to answer this by looking at the atmosphere of planets everywhere. Comparing the composition of planets in our solar system to those outside of the solar system will let us answer whether they were born in similar ways or not,” Welbanks said. “What is very interesting about our result is that the overall composition of HD 189733 b is very much like that of Jupiter. It’s almost like this far-away exoplanet is just like Jupiter, but hot. Perhaps this planet had a very similar upbringing to Jupiter’s.”

JWST’s capability to identify key molecules such as hydrogen sulfide opens up new avenues for exploring the diversity and complexity of exoplanetary atmospheres. As with recent discoveries led by the ASU team, the James Webb Space Telescope is opening new avenues for the understanding of planets and our place in the universe. 

Additional authors include Drake Deming, Jegug Ih, Arjun B. Savel, Eliza M.-R. Kempton and Matt Nixon of University of Maryland; Julie Inglis and Heather A. Knutson of California Institute of Technology; Michael Zhang of University of Chicago; Joshua Lothringer of Utah Valley University; Julianne I. Moses and Gregory Henry of Tennessee State University; Everett Schlawin of University of Arizona; David K. Sing of Johns Hopkins; and Thomas Greene of NASA Ames Research Center.

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