This Nearby Exoplanet Is Hot, Dangerous—and Smells Like Rotten Eggs

An exoplanet in our celestial ‘neighborhood,’ located about 64 light-years away, was already known for its extreme weather. Any visitor willing to brave the 1,700 degree Fahrenheit temperatures would also have to put up with a rain of molten glass that blows sideways in the world’s fierce wind.

But a new study published Monday in the journal Nature suggests that’s not the end of it. According to new data from the James Webb Space Telescope, the cobalt blue planet—called HD 189733b—literally stinks.

“If your nose could work at [roughly 1,700 degrees] ... the atmosphere would smell like rotten eggs,” Guangwei Fu, an astrophysicist at Johns Hopkins University who led the research, tells BBC News’ Maddie Molloy.

The exoplanet’s unpleasant aroma occurs because its atmosphere contains trace amounts of hydrogen sulfide—the same molecule given off when your eggs go bad. This discovery marks the first time astronomers have observed hydrogen sulfide on a planet outside our solar system.

Given these extreme conditions, it’s exceedingly unlikely that life exists on HD 189733b. But as a relatively nearby exoplanet, the world is a valuable site for researchers.

“While we are not searching for life on HD 189733b—it is too hot, made up mostly of hydrogen and helium, it’s not like Earth, et cetera—understanding its atmosphere allows us to understand how physics and chemistry behave under different environments and to begin to put together the ‘recipe’ for forming planets,” study co-author Luis Welbanks, an astrophysicist at Arizona State University, tells Reuters’ Will Dunham.

Astronomers refer to exoplanets like HD 189733b as ‘hot Jupiters’ due to their similar size and composition to our nearest gas giant. But these exoplanets have much higher temperatures. HD 189733b, for example, orbits about 13 times closer to its star than Mercury is to our sun.

HD 189733b is the nearest hot Jupiter, and it has been one of the most-studied exoplanets since its discovery in 2005. In 2012, astronomers using the Hubble Space Telescope observed an X-ray flare that erupted from the exoplanet’s host star, blowing away part of its atmosphere. It was also the first planet outside our solar system to have its color directly measured.

But the James Webb Space Telescope’s ability to look beyond our solar system with high precision and infrared light is revealing new details, such as the planet’s smell.

NASA | Exoplanet Atmosphere Blasted by Stellar Flare

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The new study also found the exoplanet contains heavy metals at concentrations akin to Jupiter’s, and the team detected water and carbon dioxide in the planet’s atmosphere. This confirms previous research and indicates that HD 189733b is more similar than thought to Jupiter, which also contains hydrogen sulfide.

Sulfur’s existence on the exoplanet is also fascinating to researchers, as the element is an essential building block of life. Astronomers are hopeful they are just at the beginning of the unexpected discoveries to come from the James Webb Space Telescope.

“HD 189733b is a benchmark planet, but it represents just a single data point,” Fu tells CNN’s Ashley Strickland. “Just as individual humans exhibit unique characteristics, our collective behaviors follow clear trends and patterns. With more datasets from Webb to come, we aim to understand how planets form and if our solar system is unique in the galaxy.”

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Rudy Molinek is Smithsonian magazine's 2024 AAAS Mass Media Fellow.