An exoplanet famous for its deadly weather has another strange trait: It smells like rotten eggs, according to new research from Johns Hopkins University based on data from the James Webb Space Telescope.

The atmosphere of HD 189733 b, a gas giant the size of Jupiter, contains small amounts of hydrogen sulfide, a molecule that not only emits a foul odor but also gives scientists new clues about how sulfur, the building block of planets, might affect the interiors and atmospheres of gaseous worlds outside the Solar System. The results are published here: Nature.

“Hydrogen sulfide is a large molecule that we didn’t know existed. “We predicted it, and we know it’s on Jupiter, but we haven’t actually detected it outside the solar system,” said Guangwei Fu, an astrophysicist at Johns Hopkins who led the study.

“We’re not looking for life on this planet because it’s too hot, but finding hydrogen sulfide is a stepping stone to finding this molecule on other planets and better understanding how different types of planets form.”

In addition to detecting hydrogen sulfide and measuring the total sulfur content in HD 189733 b’s atmosphere, Fu’s team accurately measured the planet’s main sources of oxygen and carbon (water, carbon dioxide, and carbon monoxide).

“Sulfur is a vital element for building more complex molecules, like carbon, nitrogen, oxygen and phosphate, so scientists need to study it further to fully understand how planets form and what they are made of,” Fu said.

Located just 64 light-years from Earth, HD 189733 b is the closest “hot Jupiter” that astronomers have been able to observe transiting in front of its star, making it a reference planet for detailed studies of exoplanet atmospheres since its discovery in 2005, Fu said.

The planet is about 13 times closer to its star than Mercury is to the Sun, and takes only two Earth days to complete an orbit. It has a scorching temperature of 1,700 degrees Fahrenheit and is notorious for its bad weather, including raining glass blowing sideways in 5,000 mph winds.

Similar to the detection of water, carbon dioxide, methane and other critical molecules on other exoplanets, Webb gives scientists a new tool to track hydrogen sulfide and measure the sulfur content of gaseous planets outside the solar system.

“Let’s say we studied 100 hotter Jupiters and they were all enriched in sulfur. What does that mean about how they were born and how they formed differently compared to our Jupiter?” Fu said.

The new data also ruled out the presence of methane in HD 189733 b with unprecedented sensitivity and infrared wavelength observations with the Webb telescope, contradicting previous claims of the molecule’s abundance in the atmosphere.

“We thought this planet was too hot to have high methane concentrations, but we now know that’s not the case,” Fu said.

The team also measured levels of heavy metals similar to those found on Jupiter, which could help scientists answer questions about how a planet’s metallicity relates to its mass, according to Fu.

Less massive ice giant planets like Neptune and Uranus contain more metal than gas giants like Jupiter and Saturn, the largest planets in the Solar System. The higher metallicity suggests that Neptune and Uranus accumulated more ice, rock, and other heavy elements than gases like hydrogen and helium when they were first forming. Scientists are testing whether this correlation also applies to exoplanets, according to Fu.

“This Jupiter-sized planet is very close to Earth and has been very well studied. Now we have this new measurement that shows that the concentration of metals on it is a very important reference point for this study of how the composition of the planet changes with its mass and radius,” Fu said.

“The findings contribute to our understanding of how planets form through the formation of more solid material after initial core formation, which is then naturally enriched by heavy metals.”

In the coming months, Fu’s team plans to monitor the sulfur content of more exoplanets and find out how high levels of this compound might affect how close they orbit their host stars.

“We want to know how such planets got there, and understanding the composition of their atmospheres will help us answer that question,” Fu said.