Webb Telescope Offers The First Glimpse Of An Exoplanet’s Interior
A surprisingly low amount of methane and a super-sized core hide within the cotton candy–like planet WASP-107 b.
The revelations, based on data obtained by the James Webb Space Telescope, mark the first measurements of an exoplanet’s core mass and will likely underpin future studies of planetary atmospheres and interiors, a key aspect in the search for habitable worlds beyond 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, atmospheric composition, and hotness of its interior, you’ve got all the pieces you need to get an idea of what’s inside and how heavy that core is,” said lead author David Sing, a Bloomberg Distinguished Professor of Earth and Planetary Sciences at Johns Hopkins University. “This is now something we can do for lots of different gas planets in various systems.”
Published today in Nature, the research shows the planet has a thousand times less methane than expected and a core 12 times more massive than Earth’s.
A giant planet wrapped by a scorching atmosphere as fluffy as cotton, WASP-107 b orbits a star about 200 light-years away. It is puffy because of its build: a Jupiter-sized world with only a tenth of that planet’s mass.
Even though it has methane—a building block of life on Earth—the planet is not considered habitable because of its proximity to its parent star and lack of a solid surface. But it could hold important clues about late-stage planetary evolution.
In a separate study published today in Nature, other scientists also spotted methane with the Webb telescope and provided similar insights about the planet’s size and density.
“We want to look at planets more similar to the gas giants in our own solar system, which have a lot of methane in their atmospheres,” Sing said. “This is where the story of WASP-107 b got really interesting, because we didn’t know why the methane levels were so low.”
The new methane measurements suggest the molecule transforms into other compounds as it flows upward from the planet’s interior, interacting with a concoction of other chemicals and starlight in the upper atmosphere. The team also measured sulfur dioxide, water vapor, carbon dioxide, and carbon monoxide—and found WASP-107 b has more heavy elements than Uranus and Neptune.
The profile of the planet’s chemistry is starting to reveal key pieces in the puzzle of how planetary atmospheres behave in extreme conditions, Sing said. His team will conduct similar observations over the next year on an additional 25 planets with the Webb telescope.
Artist’s concept of WASP-107 b, a warm Neptune exoplanet about 200 light-years away. IMAGE CREDIT: ROBERTO MOLAR CANDANOSA/JOHNS HOPKINS UNIVERSITY
“We had never been able to study this mixing process in an exoplanet atmosphere in detail, so this will go a long way in understanding how these dynamic chemical reactions operate,” Sing said. “It’s something we definitely need as we start looking at rocky planets and biomarker signatures.”
Scientists had speculated that the planet’s overinflated radius resulted from a source of heat inside, said Zafar Rustamkulov, a Johns Hopkins doctoral student in planetary science who co-led the research. By combining atmospheric and interior physics models with Webb’s data of WASP-107 b, the team accounted for how the planet’s thermodynamics influences its observable atmosphere.
“The planet has a hot core, and that heat source is changing the chemistry of the gases deeper down, but it’s also driving this strong, convective mixing bubbling up from the interior,” Rustamkulov said. “We think this heat is causing the chemistry of the gases to change, specifically destroying methane and making elevated 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 exoplanet and the top of its atmosphere, Rustamkulov said. Last year the Webb telescope spotted sulfur dioxide about 700 light-years away in a different exoplanet called WASP-39, providing the first evidence of an atmospheric compound created by starlight-driven reactions.
The Johns Hopkins team is now focusing on what might be keeping the core hot, and expects forces might be in play similar to those causing high and low tides in Earth’s oceans. They plan to test whether the planet is being stretched and pulled by its star and how that might account for the core’s high heat.
Other study authors are Daniel P. Thorngren and Elena Manjavacas of Johns Hopkins University; Joanna K. Barstow of the Open University; Pascal Tremblin of Université Paris-Saclay; Catarina Alves de Oliveira, Stephan M. Birkmann, and Pierre Ferruit of the European Space Agency; Tracy L. Beck, Néstor Espinoza, Amélie Gressier, Marco Sirianni, and Jeff A. Valenti of the Space Telescope Science Institute; Ryan C. Challener of Cornell University; Nicolas Crouzet, Giovanna Giardino, and Nikole K. Lewis of Leiden University; Elspeth K. H. Lee; Roberto Maiolino of University of Cambridge; and Bernard J. Rauscher of NASA Goddard Space Flight Center.
This research is based on data obtained from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy Inc., under NASA contract NAS 5-03127.
A warm Neptune’s methane reveals core mass and vigorous atmospheric mixing, Nature
A warm Neptune’s methane reveals core mass and vigorous atmospheric mixing
Observations of transiting gas giant exoplanets have revealed a pervasive depletion of methane, which has only recently been identified atmospherically. The depletion is thought to be maintained by disequilibrium processes such as photochemistry or mixing from a hotter interior. However, the interiors are largely unconstrained along with the vertical mixing strength and only upper limits on the CH4 depletion have been available. The warm Neptune WASP-107 b stands out among exoplanets with an unusually low density, reported low core mass, and temperatures amenable to CH4 though previous observations have yet to find the molecule. Here we present a JWST NIRSpec transmission spectrum of WASP-107 b which shows features from both SO2 and CH4 along with H2O, CO2, and CO. We detect methane with 4.2σ significance at an abundance of 1.0±0.5 ppm, which is depleted by 3 orders of magnitude relative to equilibrium expectations. Our results are highly constraining for the atmosphere and interior, which indicate the envelope has a super-solar metallicity of 43±8× solar, a hot interior with an intrinsic temperature of Tint=460±40 K, and vigorous vertical mixing which depletes CH4 with a diffusion coefficient of Kzz = 1011.6±0.1 cm2/s. Photochemistry has a negligible effect on the CH4 abundance, but is needed to account for the SO2. We infer a core mass of 11.5+3.0−3.6 M⊙, which is much higher than previous upper limits, releasing a tension with core-accretion models.
David K. Sing (1,2), Zafar Rustamkulov (1), Daniel P. Thorngren (2), Joanna K. Barstow (3), Pascal Tremblin (4,5), Catarina Alves de Oliveira (6), Tracy L. Beck (7), Stephan M. Birkmann (6), Ryan C. Challener (8), Nicolas Crouzet (9), Néstor Espinoza (7), Pierre Ferruit (6), Giovanna Giardino (10), Amélie Gressier (7), Elspeth K. H. Lee (11), Nikole K. Lewis (8), Roberto Maiolino (12), Elena Manjavacas (2,13), Bernard J. Rauscher (14), Marco Sirianni (15), Jeff A. Valenti (7) ((1) Department of Earth & Planetary Sciences, Johns Hopkins University, (2) Department of Physics & Astronomy, Johns Hopkins University, (3) School of Physical Sciences, The Open University, (4) Université Paris-Saclay, UVSQ, CNRS, CEA, Maison de la Simulation, (5) Université Paris-Saclay, Université Paris Cité, CEA, CNRS, AIM, (6) European Space Agency, European Space Astronomy Centre, (7) Space Telescope Science Institute, (8) Department of Astronomy and Carl Sagan Institute, Cornell University, (9) Leiden Observatory, Leiden University, (10) ATG Europe for the European Space Agency, ESTEC, (11) Center for Space and Habitability, University of Bern, (12) University of Cambridge, (13) AURA for the European Space Agency, (14) NASA Goddard Space Flight Center, (15) European Space Agency, ESA Office, STScI)
Comments: Published in Nature at this URL, this https URL . This is the authors version of the manuscript, 20 pages including Methods. Data from Figs. 1, 2, and 3 are available at this URL, this https URL
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2405.11027 [astro-ph.EP] (or arXiv:2405.11027v1 [astro-ph.EP] for this version)
Related DOI:
https://doi.org/10.1038/s41586-024-07395-z
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Submission history
From: David Sing
[v1] Fri, 17 May 2024 18:01:02 UTC (3,082 KB)
https://arxiv.org/abs/2405.11027
astrobiology
