An exoplanet the size of Jupiter It has long intrigued astronomers because of its scorching temperatures, howling winds and sideways rain made of glass. Now, data from the James Webb Space Telescope has revealed another intriguing feature of the planet known as HD 189733b: he smells like rotten eggs.
Researchers who study the atmosphere of HD 189733b used Webb’s observation to detect small amounts of hydrogen sulfide — a colorless gas that gives off a strong sulfuric smell and has never been detected outside our solar system. The discovery advances knowledge about the potential composition of exoplanets.
The findings, compiled by a team from several institutions, were published on Monday (8) in the journal Nature.
An eccentric planet with a deadly climate
Scientists first discovered HD 189733b in 2005 and later identified the gas giant as a “hot Jupiter” — a planet that has a similar chemical composition to Jupiter, the largest planet in our solar system, but with scorching temperatures. Located just 64 light-years from Earth, HD 189733b is the closest hot Jupiter that astronomers can study as the planet passes in front of its star. For this reason, it is one of the most studied exoplanets.
“HD 189733 b is not only a gas giant planet, but also a ‘giant’ in the field of exoplanets because it is one of the first transiting exoplanets ever discovered,” says study lead author Guangwei Fu, an astrophysicist at Johns Hopkins University, in an email. “It is the anchor point for much of our understanding of the chemistry and atmospheric physics of exoplanets.”
The planet is about 10% larger than Jupiter, but much hotter because it is 13 times closer to its star than Mercury is to our Sun. HD 189733b takes only about two Earth days to complete a single orbit around its star. star, says Fu.
This proximity to the star gives the planet a scorching average temperature of 1,700 degrees Fahrenheit (926 degrees Celsius) and strong winds that cause glass-like silicate particles to rain sideways from the high clouds around the planet at 5,000 miles per hour (8,046 kilometers per hour).
A surprising smell
When astronomers decided to use the Webb telescope to study the planet and see what infrared light, which is invisible to the human eye, could reveal in HD 189733b’s atmosphere, they were in for a surprise.
Hydrogen sulfide is present on Jupiter and has been predicted to exist on gas giant exoplanets, but evidence of the molecule has been elusive outside our solar system, says Fu.
“Hydrogen sulfide is one of the main reservoirs of sulfur within planetary atmospheres,” he says. “The high precision and infrared capability of the (Webb telescope) allows us to detect hydrogen sulfide for the first time on exoplanets, which opens a new spectral window for studying the chemistry of sulfur in exoplanet atmospheres. This helps us understand what exoplanets are made of and how they formed.”
Additionally, the team detected water, carbon dioxide and carbon monoxide in the planet’s atmosphere, according to Fu — meaning these molecules could be common on other gas giant exoplanets.
Although astronomers do not expect life to exist on HD 189733b because of its scorching temperatures, the detection of a basic element like sulfur on an exoplanet sheds light on planet formation, according to Fu.
“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 are made of.” , says Fu.
Molecules with distinct smells, such as ammonia, have previously been detected in other exoplanet atmospheres.
But Webb’s capabilities allow scientists to identify specific chemicals in atmospheres around exoplanets in greater detail than ever before.
Planetary heavy metals
In our solar system, ice giants such as Neptune and Uranus, although less massive overall, contain more metals than the gas giants Jupiter and Saturn, which are the largest planets, suggesting that there may be a correlation between metal content and pasta.
Astronomers believe that more ice, rock and metals — rather than gases like hydrogen and helium — were involved in the formation of Neptune and Uranus.
The Webb data also showed levels of heavy metals in HD 189733b similar to those found on Jupiter.
“Now we have this new measurement to show that, in fact, the concentrations of metals (that the planet has) provide a very important anchor point for this study of how the composition of a planet varies with its mass and radius”, says Fu . “The findings support our understanding of how planets form by creating more solid material after the initial core forms and then are naturally enriched with heavy metals.”
Now, the team will look for signatures of sulfur on other exoplanets and determine whether high concentrations of the compound influence the proximity of some planets to their host stars.
“HD 189733b is a reference planet, but it only represents one data point,” says Fu. “Just as individual humans exhibit unique characteristics, our collective behaviors follow clear trends and patterns. With more Webb datasets to come, we hope to understand how planets form and whether our solar system is unique in the galaxy.”
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