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The Webb Space Telescope offers the first glimpse into the interior of an extrasolar planet

Methane found in WASP-107 b reveals core mass and stormy sky

An artist's concept of WASP-107 b shows turbulent atmospheric mixing within the planet's gas mantle. Credit: Roberto Muller Candanosa/Johns Hopkins University NASA, ESA, CSA, Ralf Crawford (STScI)
An artist's rendering of WASP-107 b shows turbulent atmospheric mixing within the planet's gas mantle. Credit: Roberto Muller Candanosa/Johns Hopkins University NASA, ESA, CSA, Ralf Crawford (STScI)

A surprisingly low amount of methane and a giant core lurk inside the planet WASP-107 b.

The discoveries, based on data obtained by the James Webb Space Telescope, mark the first measurements of the mass of the core of an extrasolar planet and will support future studies of planetary atmospheres and interiors, which are a key part of the search for viable worlds outside our solar system. .

"Looking into the interior of a planet hundreds of light-years away sounds almost impossible, but when you know the mass, radius, composition of the atmosphere and the temperature of the interior of the star, you have all the pieces you need to get an idea of ​​what's inside and how heavy the core is, ” said lead author David Singh, Distinguished Professor of Earth and Planetary Sciences at Johns Hopkins University. "This is something we can now do for many gas stars in different systems."

The study, published today in Nature, shows that the star has a thousand times less methane than expected and a core that is 12 times larger than Earth's.

A giant planet with a hot, cotton-wool-soft atmosphere, WASP-107 b orbits a star about 200 light-years away. It is soft because of its structure: a Jupiter-sized world with one-tenth the mass of Jupiter.

Although it has methane - a building block of life on Earth - the star is not considered habitable due to its proximity to its parent star and the lack of a solid surface. But it could hold important clues about the late evolution of planets.

In a separate study published today in Nature, other scientists also observed methane with the Webb telescope and provided similar insights into the star's density magnitude.

"We want to look at stars that are more like the gas giants in our solar system, that have a lot of methane in their atmospheres," Singh said. "That's where the WASP-107 b story gets really interesting, because we didn't know why the methane levels were so low."

The new measurements of methane indicate that the molecule turns into other compounds as it flows up from the star's interior, interacting with a mixture of other chemicals and starlight in the upper atmosphere. The team also measured sulfur dioxide, water vapor, carbon dioxide and carbon monoxide – and found that WASP-107 b has more heavy elements than Uranus and Neptune.

Profiling the star's chemistry is beginning to reveal key pieces of the puzzle of how stellar atmospheres behave under extreme conditions, Singh said. His team will make similar observations next year of 25 more stars with the Webb Telescope.

"We've never been able to study this mixing process in the atmosphere of an extrasolar planet in such detail, so this will go a long way in understanding how these dynamic chemical reactions work," Singh said. "That's something we definitely need as we start looking at rocky planets and biometric signatures."

Scientists have hypothesized that the star's inflated radius is due to an internal heat source, said Zafar Rostamkolov, a doctoral student in planetary sciences at Johns Hopkins University who led the study. By combining atmospheric and surface physics models with web data on WASP-107 b, the team explained how the star's thermodynamics affects its observed atmosphere.

"The star has a hot core, and that heat source changes the chemistry of the gases at depth, but it also drives this strong convective mixing that emanates from the interior," Rostamkolov said. "We think that this heat causes the chemistry of the gases to change, especially the destruction of methane and the creation of increased amounts of carbon dioxide and carbon monoxide."

The new findings also represent the clearest connection scientists have been able to make about the interior of an extrasolar star and the top of its atmosphere, Rostamkolov said. Last year, the Webb Telescope spotted sulfur dioxide about 700 light-years away in another exoplanet called WASP-39, providing the first evidence of an atmospheric compound formed by reactions driven by starlight.

The Johns Hopkins team is now focusing on what might be keeping the core warm, predicting that forces may be at work similar to those that cause high and low tides in Earth's oceans. They plan to test whether the star is being stretched and pulled by its star and how this might explain the high temperature of the core.

Other authors of the study are Daniel P. Thorngren and Elena Menjavecks of Johns Hopkins University; Joanna K. Barstow from the Open University; Pascal Tremblin of the University of Paris-Saclay; Katrina Alves de Oliveira, Stefan M. Birkman, and Pierre Fruet of the European Space Agency; Tracy L. Beck, Nestor Espinoza, Emily Grasier, Marco Siriani, and Jeff A. Volenti of the Space Telescope Institute; Ryan S. Chalner of Cornell University; Nicolas Crozet, Giovanna Giardino and Nicole K. Lewis of Leiden University; Elsfat K. God. to me; Roberto Maiolino of the University of Cambridge; and Bernard G. Rauscher from NASA's Goddard Space Flight Center.

This study is based on data obtained from the Space Telescope Facility, which is managed by the Association of Universities for Research in Astronomy, under NASA contract NAS 5-03127.

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