July 12, 2024
1 Solar System Way, Planet Earth, USA

A giant, stinky exoplanet smells like rotten eggs

Stinky exoplanet: Large planet with bands of blueish and whitish clouds orbiting a large yellow star.
Artist's conception of HD 189733 b. A new study by researchers at Johns Hopkins University has found that the gigantic, stinky exoplanet smells like rotten eggs. Image via Roberto Molar Candanosa/ Johns Hopkins University.
  • Gas giant exoplanet HD 189733 b smells like rotten eggsAstronomers say the pungent odor is due to hydrogen sulfide gas present in the world's atmosphere.
  • The amount of hydrogen sulfide It is similar to that of Jupiter's atmosphere.
  • The discovery provides clues on how gas giant planets form and evolve.

When studying at a distance exoplanets – or worlds orbiting other stars – astronomers examine what they look like, how big and massive they are, what kind of atmosphere they have, and more. But what about how smell? We now know that at least one exoplanet smells pretty bad… at least to our human sense of smell. On July 8, 2024, astronomers at Johns Hopkins University in Baltimore, Maryland, saying that the Jupiter-sized exoplanet HD 189733 b smells like rotten eggs, thanks to hydrogen sulfide in its atmosphere. They used NASA James Webb Space Telescope to make observations.

The researchers published his peer reviewed findings in Nature July 8, 2024.

Meet the giant exoplanet HD 189733 b

HD 189733 b, discovered in 2005, is a gas giant exoplanet about the same size as Jupiter. 64 light years From Earth, it is the closest known. Hot Jupiter– A C-type exoplanet that transits in front of its star as seen from Earth. This makes it ideal for atmospheric study by astronomers. Hot Jupiters are gas giants that orbit very close to their stars, unlike Jupiter and Saturn in our solar system.

The planet orbits 13 times closer to its star than Mercury does to our own Sun. It orbits its star in just two days.

The atmosphere of this smelly exoplanet contains carbon dioxide, carbon monoxide, oxygen, and water. Because it's so close to its star, it's scorching hot and the weather is deadly. Temperatures reach 1,700 degrees Fahrenheit (930 C) and winds howl at 5,000 mph (8,000 kph). On this world, it doesn't rain water, but rather tiny particles of oxygen. glassExtreme winds cause the glass to fly sideways as it falls.

But there's something else on HD 189733 b, which actually makes up most of its atmosphere: hydrogen sulfide. That's why the planet smells so bad.

Stinky exoplanet smells like rotten eggs

Hydrogen sulfide is known to be a smelly gas. On Earth, it is one of the many gases released by Volcanic eruptionsScientists didn't know they would find it in HD 189733 b, even though they predicted it should be there. Guangwei Fuastrophysicist at Johns Hopkins, was the lead author of the new study. He said:

Hydrogen sulfide is an important molecule that we didn't know existed. We had predicted its existence and we know it's on Jupiter, but we hadn't 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 step towards finding this molecule on other planets and better understanding how different types of planets form.

Clues to planetary formation

Hydrogen sulfide is a central part of the sulfur cyclehe biogeochemical cycle The discovery of hydrogen sulfide will help scientists learn more about how planets form. Sulfur is an essential part of that process, as Fu explained:

Sulfur is a vital element for building more complex molecules, and like carbon, nitrogen, oxygen and phosphate, scientists need to study it further to fully understand how planets form and what they are made of.

Webb will help scientists detect and study hydrogen sulfide and hydrogen sulfide on other gas giant exoplanets as well. Fu said:

Let's say we study 100 other hot Jupiters and they're all enriched with sulfur. What does that say about how they were born and how they form differently compared to our own Jupiter?

Volcano with dark smoke coming out of its summit, with snow on its slopes and a dark, gloomy sky behind it.
View larger. | Eruption of the Augustine volcano in Alaska on January 12, 2006. On Earth, hydrogen sulfide is one of the many gases released by Volcanic eruptionsImage via Game McGimsey/ Wikimedia Commons (public domain).

Without methane

While Webb confirmed the presence of hydrogen sulfide on HD 189733 b, he also established the absence of methane. Astronomers had suspected that the planet probably wouldn't have much, if any, methane due to its high temperatures. Fu said:

We had been thinking that this planet was too hot to have high concentrations of methane, and now we know that is not the case.

Heavy metals similar to Jupiter

Webb also found heavy metals in quantities similar to those on Jupiter. In general, heavy metals are defined as metallic elements with relatively high densities, atomic weights either atomic numbersFu said:

This planet, with a mass similar to that of Jupiter, is very close to Earth and has been very well studied. Now we have this new measurement which shows that, indeed, the concentrations of metals it contains provide a very important support point for this study of how the composition of a planet varies with its mass and radius.

The finding is interesting, since in our solar system, the ice giants Uranus and Neptune contain more heavy metals than the gas giants Jupiter and Saturn. Scientists say this means Uranus and Neptune accumulated more ice, rock and other heavy elements relative to gases like hydrogen and helium when they first formed. Since the amount of heavy metals in HD 189733 b is similar to that of Jupiter, this is consistent with what we know so far about how planets form. Fu added:

The findings support our understanding of how planets form through the creation of more solid material after initial core formation and then becoming naturally enriched with heavy metals.

Researchers now plan to study additional exoplanets and see how they compare to the stinking exoplanet HD 189773 b.

Bottom line: Astronomers say the giant, stinky exoplanet HD 189733 b smells as bad as rotten eggs, thanks to hydrogen sulfide in its atmosphere.

Source: Hydrogen sulfide and metal-enriched atmosphere for a Jupiter-mass exoplanet

By Johns Hopkins University

Read more: Gas giant exoplanets cling to their parent stars

Read more: First direct image of two giant exoplanets orbiting a Sun-like star

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