Image: Artist’s impression of nearby hot Jupiter HD 189733 b. Credit: Roberto Molar Candanosa/Johns Hopkins University.
The planet, a Jupiter-sized gas giant named HD 189733 b, has an atmosphere made up mostly of hydrogen sulfide: a molecule that not only smells bad, but is also giving scientists new clues about how sulfur — a planetary building block — affects the interior and outer atmospheres of gaseous worlds outside the solar system.
“Hydrogen sulfide is an important molecule that we know exists on Jupiter, but we have yet to find it on a planet outside our solar system,” said Guangwei Fu, an astrophysicist at Johns Hopkins University who led the study. “We are not looking for life on this planet because it is too hot, but the discovery of hydrogen sulfide is a precursor to finding this molecule on other planets and gaining more insight into how different types of planets form.”
In addition to detecting hydrogen sulfide and measuring the total amount of sulfur in HD 189733 b’s atmosphere, Fu’s team also accurately measured the planet’s main sources of oxygen and carbon: water, carbon dioxide, and carbon monoxide. In addition, the new data rule out that HD 189733’s atmosphere is rich in methane, as previous publications have suggested.
“Hot Jupiter”
At 64 light-years away, HD 189733 b is the closest “hot Jupiter” that astronomers see passing in front of its star at regular intervals. This makes it an important reference point for detailed studies of exoplanet atmospheres. It is about thirteen times closer to its star than Mercury is to the Sun and requires only two Earth days to complete one orbit. With temperatures reaching 1,000 degrees Celsius, the planet is not only extremely hot, it is also known for its catastrophic weather conditions, including glassy rains blown by winds of up to 8,000 km/h.
The research team also measured the heavy metal content of HD 189733, a finding that could help scientists answer the question of how a planet’s metallicity is related to its mass. Less massive ice giants like Neptune and Uranus have more metals than gas giants like Jupiter and Saturn, the largest planets in our solar system. This suggests that Neptune and Uranus accumulated proportionately more ice, rock, and other heavy elements than lighter gases like hydrogen and helium during the early stages of their formation. Planetary scientists are now investigating whether this connection also applies to exoplanets.
