The James Webb Space Telescope (JWST) has made a groundbreaking discovery about one of the closest “hot Jupiter” exoplanets to Earth, HD 189733 b. This planet, already known for its extreme weather conditions, has now been found to have an atmosphere that stinks like rotten eggs due to the presence of hydrogen sulfide.
Unfriendly World
HD 189733 b, discovered in 2005, is located about 64 light years away from Earth in the constellation Vulpecula. It is roughly 1.13 times the size and mass of Jupiter and orbits its star at a distance of approximately 3 million miles (4.8 million km). This proximity results in an extremely hot atmosphere with temperatures around 1,700 degrees Fahrenheit (927 degrees Celsius), making it an inhospitable environment.
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Hydrogen Sulfide: The Source of the Stench
The discovery of hydrogen sulfide, a molecule that gives off the stench of rotten eggs, marks a significant milestone in the study of exoplanetary atmospheres. Guangwei Fu, an astrophysicist at Johns Hopkins University and the leader of the research team, emphasized the importance of this finding. “Hydrogen sulfide is a major molecule that we didn’t know was there. We predicted it would be, and we know it’s in Jupiter, but we hadn’t really detected it outside the solar system,” he said.
Atmospheric Composition and Formation Insights
In addition to hydrogen sulfide, the JWST detected water, carbon dioxide, and carbon monoxide in the atmosphere of HD 189733 b. The presence of these molecules, along with the absence of methane, provides valuable information about the planet’s atmospheric composition and its formation processes.
“Sulfur is a vital element for building more complex molecules, and—like carbon, nitrogen, oxygen, and phosphate—scientists need to study it more to fully understand how planets are made and what they’re made of,” Fu explained. The detection of hydrogen sulfide on HD 189733 b could help scientists understand how the atmospheres of giant gas planets are influenced by sulfur, an important element in planetary formation.
Extreme Weather Conditions
HD 189733 b is notorious for its extreme weather conditions. The planet is tidally locked to its star, meaning one side always faces the star while the other side remains in perpetual darkness. The dayside is bombarded by intense radiation, causing temperatures high enough to vaporize glass. The planet’s 5,000 mph (8,046 kph) winds blow this glass vapor to the cooler nightside, where it condenses and rains down in glass shards that slice sideways at high speeds.
Metallicity and Planet Formation
The JWST’s observations also revealed that HD 189733 b has a high concentration of heavy metals, comparable to Jupiter. This finding supports the idea that the planet’s composition varies with its mass and radius, providing insights into the formation of planets. In the solar system, smaller ice giants like Neptune and Uranus are richer in metals than the larger gas giants Jupiter and Saturn. This relationship between mass and metallicity is a key area of study for Fu and his team.
“This Jupiter-mass planet is very close to Earth and has been very well studied. Now we have this new measurement to show that indeed the metal concentrations it has provide a very important anchor point to this study of how a planet’s composition varies with its mass and radius,” Fu said.
The team aims to track sulfur as it moves through the atmospheres of other exoplanets, helping to determine how concentrations of this element vary with distance from a parent star. This research will enhance our understanding of how different types of planets form and evolve.
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“HD 189733 b is a benchmark planet, but it represents just a single data point,” Fu noted. “With more datasets from Webb to come, we aim to understand how planets form and if our solar system is unique in the galaxy.”