Using the James Webb Space Telescope (JWST), astronomers have discovered that one of the closest "hot Jupiter" planets to Earth stinks of rotten eggs. The planet is already notorious for its deadly rains of glass, extreme temperatures and 5,000 mph (8,046 km/h) sideways winds, but this discovery makes it an even less friendly world.
The JWST's conclusion comes after it discovered hydrogen sulfide, a molecule that gives off the odor of rotten eggs, in the exoplanet's atmosphere.
This could give scientists insight into how the atmospheres of large gas planets are affected by the presence of sulfur, an element considered important in planetary formation.
The exoplanet in question is HD 189733 b, a planet about 1.13 times the size and mass of Jupiter. The planet, discovered in 2005, is located about 65 light-years from Earth in the constellation Vulpecula.
HD 189733 b orbits its star at a distance of about 3 million miles (4.8 million km), or about 3% of the distance between Earth and the Sun. Its hot atmosphere and glass-soaked clouds give it a deceptive, almost placid, blue-white marble appearance.
"Hydrogen sulfide is an important molecule that we didn't know was there. We predicted it would be there and we know it's in Jupiter, but we hadn't really discovered it outside the solar system," team leader Guangwei Fu, an astrophysicist at Johns Hopkins, said in a statement. "We're not looking for life on this planet because it's way too hot, but finding hydrogen sulfide is a stepping stone to finding this molecule on other planets and gaining more insight into how different types of planets form."
Fu and colleagues were not only able to detect hydrogen sulfide in HD 189733 b's atmosphere, but they also measured the planet's total sulfur content. Additionally, the team was able to determine the sources of the exoplanet's oxygen and carbon, finding water, carbon dioxide, and carbon monoxide.
"Sulfur is an essential 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 continued. "Suppose we study another 100 hot Jupiters, and they're all enriched with sulfur. What does that tell us about how they were born and how they form differently compared to our own Jupiter?"
Related: Scientists find surprising ingredient in exoplanet cake mix: sulfur dioxide
Is HD 189733 b 'more metallic' than Jupiter?
Despite its unstable and smelly nature, the star it orbits, HD 189733, is happy to keep this exoplanet close. HD 189733 b orbits its star so tightly that its orbit would fit around the sun 13 times that of Mercury, the solar system's first planet.
This proximity makes HD 189733 ba a "hot Jupiter" planet, a world as large as or larger than the most massive planet in the solar system, and one that orbits much closer to its star than the solar system's gas giant does to the Sun. HD 189733 b is, in fact, the closest hot Jupiter to Earth known to cross, or "outcross," the face of its star.
This proximity to its star not only means that HD 189733 b completes an orbit in just 2.2 Earth days, but it also means that the Jupiter-sized planet has a temperature of about 1,700 degrees Fahrenheit (927 degrees Celsius). That's more than hot enough to melt lead.
HD 189733 b is "tidal" to its star. This means that one side of the planet, its "day side," is permanently facing HD 189733 and is bombarded by radiation, while the other side, its "night side," is always facing space. The heat of the planet's day side is enough to vaporize glass, and the world's 5,000 mph (8,046 km/h) winds blow this glass vapor toward the cooler night side, where it condenses and forms glass rain. Thanks to HD 189733 b's extreme winds, this glass rain doesn't just fall, though; it cuts sideways at high speeds.
The team found that this smelly, scary planet is devoid of methane. Previously, this molecule was thought to be abundant in HD 189733 b's atmosphere, but this JWST study ruled that out.
"We thought this planet was too hot for high methane concentrations, but now we know that's not the case," Fu said.
This planet is definitely extreme, but how "metal" is this planet?
To astronomers, "metals" means any element heavier than hydrogen and helium, the two lightest elements in the universe. One thing this team is really interested in is the levels of metals on planets, which could help them determine how a world's "metallicity" correlates with its mass.
In the solar system, the smaller ice giants Neptune and Uranus are richer in metals than the larger gas giants Jupiter and Saturn. This suggests to scientists that the ice giants accumulated more ice, rock and other heavy elements relative to hydrogen and helium as they formed. Fu and his team are testing whether this relationship between mass and metals also holds for planets outside the system.
"This Jupiter-mass planet is very close to Earth and has been very well studied. Now we have this new measurement to show that the metal concentrations it has are indeed a very important anchor for this study of how a planet's composition varies with its mass and radius," Fu said. "The findings support our understanding of how planets form by creating more solid material after initial core formation and then naturally being reinforced with heavy metals."
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The team now wants to track sulfur as it moves through the atmospheres of other exoplanets. This will help them determine how concentrations of this element vary with distance from a host star.
"We want to know how these kinds of planets got there. Understanding their atmospheric composition will help us answer that question," Fu concluded.
The team's research was published Monday (July 8) in the journal Nature.
