A high internal heat flux and large core in a warm Neptune exoplanet

Luis Welbanks¹, Taylor J Bell^{2

3}, Thomas G Beatty⁴, Michael R Line⁵, Kazumasa Ohno^{6

7}, Jonathan J Fortney⁶, Everett Schlawin⁸, Thomas P Greene³, Emily Rauscher⁹, Peter McGill¹⁰, Matthew Murphy⁸, Vivien Parmentier¹¹, Yao Tang⁶, Isaac Edelman², Sagnick Mukherjee⁶, Lindsey S Wiser⁵, Pierre-Olivier Lagage¹², Achrène Dyrek¹², Kenneth E Arnold⁴

Affiliations

¹ School of Earth and Space Exploration, Arizona State University, Tempe, AZ, USA. luis.welbanks@asu.edu.
² Bay Area Environmental Research Institute, NASA's Ames Research Center, Moffett Field, CA, USA.
³ Space Science and Astrobiology Division, NASA's Ames Research Center, Moffett Field, CA, USA.
⁴ Department of Astronomy, University of Wisconsin-Madison, Madison, WI, USA.
⁵ School of Earth and Space Exploration, Arizona State University, Tempe, AZ, USA.
⁶ Department of Astronomy and Astrophysics, University of California, Santa Cruz, Santa Cruz, CA, USA.
⁷ Division of Science, National Astronomical Observatory of Japan (NAOJ), Tokyo, Japan.
⁸ Steward Observatory, University of Arizona, Tucson, AZ, USA.
⁹ Department of Astronomy, University of Michigan, Ann Arbor, MI, USA.
¹⁰ Space Science Institute, Lawrence Livermore National Laboratory, Livermore, CA, USA.
¹¹ Laboratoire Lagrange, Observatoire de la Côte d'Azur, Université Côte d'Azur, Nice, France.
¹² Université Paris-Saclay, Université Paris Cité, CEA, CNRS, AIM, Gif-sur-Yvette, France.

PMID: 38768634
DOI: 10.1038/s41586-024-07514-w

A high internal heat flux and large core in a warm Neptune exoplanet

Luis Welbanks et al. Nature. 2024 Jun.

. 2024 Jun;630(8018):836-840.

doi: 10.1038/s41586-024-07514-w. Epub 2024 May 20.

Authors

Affiliations

¹ School of Earth and Space Exploration, Arizona State University, Tempe, AZ, USA. luis.welbanks@asu.edu.
² Bay Area Environmental Research Institute, NASA's Ames Research Center, Moffett Field, CA, USA.
³ Space Science and Astrobiology Division, NASA's Ames Research Center, Moffett Field, CA, USA.
⁴ Department of Astronomy, University of Wisconsin-Madison, Madison, WI, USA.
⁵ School of Earth and Space Exploration, Arizona State University, Tempe, AZ, USA.
⁶ Department of Astronomy and Astrophysics, University of California, Santa Cruz, Santa Cruz, CA, USA.
⁷ Division of Science, National Astronomical Observatory of Japan (NAOJ), Tokyo, Japan.
⁸ Steward Observatory, University of Arizona, Tucson, AZ, USA.
⁹ Department of Astronomy, University of Michigan, Ann Arbor, MI, USA.
¹⁰ Space Science Institute, Lawrence Livermore National Laboratory, Livermore, CA, USA.
¹¹ Laboratoire Lagrange, Observatoire de la Côte d'Azur, Université Côte d'Azur, Nice, France.
¹² Université Paris-Saclay, Université Paris Cité, CEA, CNRS, AIM, Gif-sur-Yvette, France.

PMID: 38768634
DOI: 10.1038/s41586-024-07514-w

Abstract

Interactions between exoplanetary atmospheres and internal properties have long been proposed to be drivers of the inflation mechanisms of gaseous planets and apparent atmospheric chemical disequilibrium conditions¹. However, transmission spectra of exoplanets have been limited in their ability to observationally confirm these theories owing to the limited wavelength coverage of the Hubble Space Telescope (HST) and inferences of single molecules, mostly H₂O (ref. ²). In this work, we present the panchromatic transmission spectrum of the approximately 750 K, low-density, Neptune-sized exoplanet WASP-107b using a combination of HST Wide Field Camera 3 (WFC3) and JWST Near-Infrared Camera (NIRCam) and Mid-Infrared Instrument (MIRI). From this spectrum, we detect spectroscopic features resulting from H₂O (21σ), CH₄ (5σ), CO (7σ), CO₂ (29σ), SO₂ (9σ) and NH₃ (6σ). The presence of these molecules enables constraints on the atmospheric metal enrichment (M/H is 10-18× solar³), vertical mixing strength (log₁₀K_zz = 8.4-9.0 cm² s^-1) and internal temperature (>345 K). The high internal temperature is suggestive of tidally driven inflation⁴ acting on a Neptune-like internal structure, which can naturally explain the large radius and low density of the planet. These findings suggest that eccentricity-driven tidal heating is a critical process governing atmospheric chemistry and interior-structure inferences for most of the cool (<1,000 K) super-Earth-to-Saturn-mass exoplanet population.

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References

1. Fortney, J. J. et al. Beyond equilibrium temperature: how the atmosphere/interior connection affects the onset of methane, ammonia, and clouds in warm transiting giant planets. Astron. J. 160, 288 (2020).
1. Kreidberg, L., Line, M. R., Thorngren, D., Morley, C. V. & Stevenson, K. B. Water, high-altitude condensates, and possible methane depletion in the atmosphere of the warm super-Neptune WASP-107b. Astrophys. J. Lett. 858, L6 (2018).
1. Lodders, K., Palme, H. & Gail, H. P. in Landolt-Börnstein - Group VI Astronomy and Astrophysics, Vol. 4B (ed. Trümper, J. E.) 712 (Springer, 2009).
1. Millholland, S., Petigura, E. & Batygin, K. Tidal inflation reconciles low-density sub-Saturns with core accretion. Astrophys. J. 897, 7 (2020).
1. Piaulet, C. et al. WASP-107b’s density is even lower: a case study for the physics of planetary gas envelope accretion and orbital migration. Astron. J. 161, 70 (2021).

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A high internal heat flux and large core in a warm Neptune exoplanet

Affiliations

A high internal heat flux and large core in a warm Neptune exoplanet

Authors

Affiliations

Abstract

References

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