ATLANTA – A Jupiter-sized exoplanet has long intrigued astronomers because of its scorching temperatures, howling winds and glassy rain. 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 tiny amounts of hydrogen sulfide—a colorless gas that emits a strong sulfuric smell and has never been seen beyond our solar system. The discovery advances what is known about the possible composition of exoplanets.
The findings, compiled by a multi-institutional team, were published Monday in the journal Nature.
A strange planet with deadly weather
Scientists first discovered HD 189733b in 2005 and later identified the gas giant as a “hot Jupiter” – a planet that has a chemical composition similar to Jupiter, the largest planet in our solar system, but with noisy 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 field of exoplanets because it is one of the first transiting exoplanets ever discovered,” said 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 atmospheric chemistry and 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 just two Earth days to complete a single orbit around its star, Fu said.
This proximity to the star gives the planet a scorching average temperature of 1,700 degrees Fahrenheit and strong winds that send glass-like silicate particles tumbling sideways from the high clouds around the planet at 5,000 miles per hour.
A surprising stench
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 in for a surprise.
Hydrogen sulfide is present on Jupiter and was predicted to exist on gas giant exoplanets, but evidence of the molecule had been elusive outside our solar system, Fu said.
“Hydrogen sulfide is one of the main reservoirs of sulfur within planetary atmospheres,” Fu said. “The high precision and infrared capability from (the Webb telescope) allow us to detect hydrogen sulfide for the first time in exoplanets, which opens a new spectral window into the study of exoplanet atmospheric sulfur chemistry. This helps us understand what exoplanets are made of and how they were created”.
In addition, the team detected water, carbon dioxide and carbon monoxide in the planet’s atmosphere, Fu said — meaning these molecules may be common on other gas giant exoplanets.
While astronomers don’t expect life to exist on HD 189733b because of its scorching temperatures, the discovery of a building block like sulfur in 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 are made of.
– Guangwei Fu, astrophysicist
“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,” Fu said.
Molecules with a distinct smell, such as ammonia, have previously been detected within the atmospheres of other exoplanets.
But Webb’s capabilities enable scientists to identify specific chemicals within the atmospheres around exoplanets in greater detail than before.
Planetary heavy metals
In our solar system, ice giants such as Neptune and Uranus, although generally less massive, contain more metals than the gas giants Jupiter and Saturn, which are the largest planets, suggesting that there may be a correlation between the content of metals and mass.
Astronomers believe that more ice, rocks and metals – rather than gases like hydrogen and helium – were involved in the formation of Neptune and Uranus.
Webb’s data also showed levels of heavy metals in HD 189733b that are similar to those found in Jupiter.
“Now we have this new measurement to show that indeed the (planet’s) metal concentrations have provided a very important anchor point 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 through the creation of harder material after initial core formation and are then naturally enhanced with heavy metals.”
Now, the team will look for signatures of sulfur in other exoplanets and determine whether high concentrations of the compound affect how certain planets form in relation to their host stars.
“HD 189733b is a standard planet, but it represents only a single data point,” Fu said. “Just as individual humans exhibit unique characteristics, our collective behaviors follow clear trends and patterns. With more data sets from Webb to come, we aim to understand how planets form and whether our solar system is unique in the galaxy.” “