The gas giants orbiting our sun show a clear picture; the larger the planet, the lower the percentage of “heavy” elements (everything but hydrogen and helium) in the planet’s atmosphere. But an international group of astronomers has found that in the galaxy, the atmospheric composition of the giant planets does not correspond to the trend of the solar system.

Using NASA’s James Webb Space Telescope (JWST), researchers found that the atmosphere of exoplanet HD149026b, a “hot Jupiter” orbiting a star similar to our Sun, is unusually rich in the heavier elements carbon and oxygen, and scientists have They discovered that it was much higher than they had expected. such a planet. Also known as “Smertrios,” HD149026b’s diagnostic carbon-oxygen ratio is high compared to our own Solar System.

“Every giant planet looks different, and with JWST we’re starting to see these differences,” said Jonathan Lunin, David S. Duncan Chair of Physical Sciences in the Faculty of Arts and Sciences and co-author of the study. “In this paper, we determined the number of molecules relative to the main gas component, which is hydrogen, the most abundant element in the universe. That tells us a lot about how this planet formed.”

Jacob Bean, professor of astronomy and astrophysics at the University of Chicago and lead author of the paper, said the giant planets of our solar system show a near-perfect correlation between both overall composition and atmospheric composition and mass. Extrasolar planets show much more variation in overall composition, but until this analysis of HD149026b, scientists didn’t know how variable their atmospheric composition was.

“We have shown conclusively that the composition of the atmospheres of giant extrasolar planets does not follow the trend so clearly seen for planets in the Solar System,” Bean said. Said. “Giant extrasolar planets display a wide variety of atmospheric compositions in addition to a wide variety of overall composition.”

Smertrios, for example, is extremely rich for its mass, said Lunin: “This is the mass of Saturn, but its atmosphere appears to contain 27 times more heavy elements than the hydrogen and helium we find on Saturn.”

This ratio, called “metallicity” (although it contains many nonmetallic elements), is useful for comparing a planet to its parent star or other planets in its system, Lunin said. Deathrios is the only known planet in this planetary system.

Another important measurement, Lunin said, is the ratio of carbon to oxygen in a planet’s atmosphere, which reveals the “description” of primordial solids in a planetary system. For Smertrios, it’s about 0.84 higher than our solar system. In our sun, this is more than one carbon (0.55) for every two oxygen atoms.

“Together, these observations paint a picture of a planet-forming disk containing abundant carbon-rich solids,” said Lunin. Said. “HD149026b took up large amounts of this material during its formation.”

While plenty of carbon seems good for life chances, a high carbon/oxygen ratio actually means less water on a planet or planetary system – a problem for life as we know it.

Lunin, who plans to observe five giant exoplanets with JWST next year, said Smertrios is an interesting first example of atmospheric composition for this particular study. More observations are needed before astronomers can identify any patterns of compositional diversity between giant planets, or in systems with many giant planets or terrestrial planets, which astronomers are beginning to document.

“The origin of this diversity is a fundamental puzzle in our understanding of planet formation,” Bean said. “We hope that further JWST atmospheric observations of exoplanets will better measure this diversity and reveal constraints on the more complex trends that may exist.”