Roberto Molar Candanosa/Johns Hopkins University
An illustration depicts exoplanet HD 189733b, a gas giant located 64 light-years away.
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A Jupiter-sized exoplanet has long intrigued astronomers for its searing temperatures, screaming winds and lateral rain made of glass. Now data from the James Webb Space Telescope has revealed another intriguing feature of the planet known as HD 189733b: it smells like rotten eggs.
Researchers studying HD 189733b’s atmosphere used Webb’s observation to spot traces of hydrogen sulfide, a colorless gas that gives off a strong sulfurous odor and has never been spotted outside our solar system. The discovery advances what is known about the potential composition of exoplanets.
The findings, compiled by a multi-institutional team, were published Monday in the journal Nature.
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 high temperatures. Located just 64 light-years from Earth, HD 189733b is the closest hot Jupiter astronomers can study as the planet passes in front of its star. For this reason, it is one of the most well-studied exoplanets.
“HD 189733 b is not only a gas giant planet, but also a ‘giant’ in the exoplanet field because it is one of the first transiting exoplanets ever discovered,” lead study author Guangwei Fu, an astrophysicist at Johns Hopkins University, said in an email. “It is the fulcrum for much of our understanding of the atmospheric chemistry and physics of exoplanets.”
Roberto Molar Candanosa/Johns Hopkins University
The exoplanet orbits very close to its host star, causing the planet to have a scorching surface temperature.
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 one orbit around its star, Fu said.
This proximity to the star gives the planet a scorching average temperature of 1,700 degrees Fahrenheit (926 degrees Celsius) and strong winds that send glassy silicate particles raining away from the high clouds surrounding the planet at speeds of 5,000 miles per hour (8,046 kilometers per hour ). .
When astronomers decided to use the Webb Telescope to study the planet to see what infrared light, which is invisible to the human eye, could reveal in HD 189733b’s atmosphere, they were surprised.
Hydrogen sulfide is present on Jupiter and is thought to exist on gas giant exoplanets, but evidence of the molecule has been elusive outside our solar system, Fu said.
“Hydrogen sulfide is one of the major reservoirs of sulfur in planetary atmospheres,” Fu said. “The high precision and infrared capabilities of (the Webb telescope) allow us to detect hydrogen sulfide for the first time on exoplanets, which opens a new spectral window into the study of atmospheric sulfur chemistry on exoplanets.” This helps us understand what exoplanets are made of and how they came to be.
The team also spotted water, carbon dioxide and carbon monoxide in the planet’s atmosphere, Fu said — meaning these molecules may be common in other gas giant exoplanets.
Although astronomers don’t expect life to exist on HD 189733b because of the hot temperatures, finding a building block like sulfur on an exoplanet sheds light on the planet’s formation, Fu said.
“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 said.
Molecules with different odors, such as ammonia, have previously been detected in the atmospheres of other exoplanets.
But Webb’s capabilities allow scientists to identify specific chemicals in the atmospheres around exoplanets in more detail than before.
In our solar system, the 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 relationship between metal content and the table.
Astronomers believe that more ice, rock and metals – rather than gases like hydrogen and helium – were involved in the formation of Neptune and Uranus.
Webb’s data also show heavy metal levels in HD 189733b that are similar to those found on Jupiter.
“Now we have this new measurement to show that indeed (the planet’s) metal concentrations provide a very important reference point for this study of how the composition of a planet 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 become enriched in heavy metals.”
The team will now search for signatures of sulfur on other exoplanets and determine whether high concentrations of the compound affect how close some planets form to their host stars.
“HD 189733b is a reference planet, but it represents only one data point,” Fu said. “Just as individuals exhibit unique characteristics, our collective behavior follows clear trends and patterns. As more data sets come in from Webb, we aim to understand how planets form and whether our solar system is unique in the galaxy.
