HD 189733 b, a gas giant similar in size to Jupiter, reveals new information about sulfur's role in planetary formation and atmospheric composition. The presence of hydrogen sulfide, a molecule previously predicted but not detected outside our solar system, offers insights into the chemistry of gas giants beyond our solar system.
"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," said Guangwei Fu, an astrophysicist at Johns Hopkins who led the research. "We're not looking for life on this planet because it's way too hot, but finding hydrogen sulfide is a stepping stone for finding this molecule on other planets and gaining more understanding of how different types of planets form."
Along with identifying hydrogen sulfide, Fu's team also measured the planet's primary oxygen and carbon sources-water, carbon dioxide, and carbon monoxide. The study highlights sulfur as a key element in forming complex molecules, necessitating further research to understand planetary construction.
At a distance of only 64 light-years, HD 189733 b is the closest "hot Jupiter" that transits its star, allowing detailed atmospheric studies since its 2005 discovery. The planet is extraordinarily close to its star, completing an orbit in just two Earth days, with surface temperatures around 1,700 degrees Fahrenheit and extreme weather conditions, including glass rain driven by 5,000 mph winds.
The Webb telescope's capabilities enable scientists to detect and study hydrogen sulfide in exoplanetary atmospheres, adding to previous findings of water, carbon dioxide, and methane in other exoplanets. "Say we study another 100 hot Jupiters and they're all sulfur enhanced. What does that mean about how they were born and how they form differently compared to our own Jupiter?" Fu said.
The new data from Webb also precisely ruled out the presence of methane in HD 189733 b, contradicting previous reports and confirming the planet's extreme heat prevents significant methane formation. The team additionally measured heavy metals in the atmosphere, a comparison to Jupiter that could inform our understanding of how planetary metallicity correlates with mass.
The findings contribute to a broader comprehension of planetary formation, indicating that less-massive icy giants like Neptune and Uranus accumulate more metals than larger gas giants like Jupiter and Saturn. Fu noted that ongoing research aims to determine if this metallicity-mass relationship holds for exoplanets as well.
"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 findings support our understanding of how planets form through creating more solid material after initial core formation and then are naturally enhanced with heavy metals."
Fu's team plans to extend their research on sulfur levels in other exoplanets to understand how these planets form near their parent stars. "We want to know how these kinds of planets got there, and understanding their atmospheric composition will help us answer that question," Fu said.
This research was supported by NASA through the JWST GO program.
Research Report:Hydrogen sulfide and metal-enriched atmosphere for a Jupiter-mass exoplanet
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