Nearby planet smells like rotten eggs

An exoplanet notorious for its deadly weather, located just 64.5 light-years from Earth, has been revealed to be hiding a strange feature in its atmosphere.

According to a new study by Johns Hopkins University of data from the James Webb Space Telescope, scientists have found that the nearby exoplanet smells like rotten eggs.

The study suggests that the atmosphere of the exoplanet HD 189733 b, a gas giant the size of Jupiter, contains trace amounts of hydrogen sulfide.

In addition to giving off a foul odor, the molecule is giving scientists new clues about how sulfur, a building block of planets, affects the interiors and atmospheres of exoplanets (planets outside our solar system).

The planet is about 13 times closer to its star than Mercury is to the Sun, and takes only about two Earth days to complete its orbit.

Temperatures are extremely high, reaching about 927 degrees Celsius, and the planet is known for its extreme weather, including glass rain that blows sideways with winds of 5,000 miles per hour.

“Hydrogen sulfide is a major molecule that we didn’t know existed,” said Guangwei Fu, an astrophysicist at Johns Hopkins University in the US, who led the study. “We expected it to happen, and we know it exists on Jupiter, but we haven’t really detected it outside the solar system. 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 gaining more understanding of how different types of planets form.”

HD 189733 b is our closest "hot Jupiter," a class of gas giant exoplanets that are similar in shape to Jupiter but have very short orbits, and their close proximity to their stars causes their surface atmospheres to heat up.

Astronomers can watch HD 189733 b as it passes in front of its star, making it a benchmark planet for detailed studies of exoplanet atmospheres since its discovery in 2005.

New data from the James Webb Space Telescope have ruled out the presence of methane in HD 189733 b. “We thought this planet was too hot to have high concentrations of methane, and now we know that’s not the case,” Fu explains.

Scientists now hope to track sulfur in more exoplanets and see how high levels of this compound affect how close they are to their host stars.

The new study was published in the journal Nature.