Exoplanets & Exomoons

Warm Giant Exoplanet Characterisation: Current State, Challenges And Outlook

By Keith Cowing
April 25, 2023
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Warm Giant Exoplanet Characterisation: Current State, Challenges And Outlook
This is an artist’s concept of a hypothetical 10-million-year-old star system. The bright blur at the center is a star much like our Sun. The other orb in the image is a gas-giant planet like Jupiter. Wisps of white throughout the image represent traces of gas.

Astronomers using NASA’s Spitzer Space Telescope have found evidence showing that gas-giant planets either form within the first 10 million years of a sun-like star’s life, or not at all. The lifespan for sun-like stars is about 10 billion years.

The scientists came to this conclusion after searching for traces of gas around 15 different sun-like stars, most with ages ranging from 3 million to 30 million years. With the help of Spitzer’s Infrared Spectrometer instrument, they were able to search for relatively warm gas in the inner regions of these star systems, an area comparable to the zone between Earth and Jupiter in our own solar system. They also used ground-based radio telescopes to search for cooler gas in the outer regions of these systems, an area comparable to the zone around Saturn and beyond.

The characterisation of giant exoplanets is crucial to constrain giant planet formation and evolution theory and for putting the solar-system’s giant planets in perspective.

Typically, mass-radius (M-R) measurements of moderately irradiated warm Jupiters are used to estimate the planetary bulk composition, which is an essential quantity for constraining giant planet formation, evolution and structure models.

The successful launch of the James Webb Space Telescope (JWST) and the upcoming ARIEL mission open a new era in giant exoplanet characterisation as atmospheric measurements provide key information on the composition and internal structure of giant exoplanets. In this review, we discuss how giant planet evolution models are used to infer the planetary bulk composition, and the connection between the compositions of the interior and atmosphere.

We identify the important theoretical uncertainties in evolution models including the equations of state, atmospheric models, chemical composition, interior structure and main energy transport processes. Nevertheless, we show that that atmospheric measurements by JWST and ARIEL and the accurate determination of stellar ages by PLATO can significantly reduce the degeneracy in the inferred bulk composition.

Furthermore, we discuss the importance of evolution models for the characterisation of direct-imaged planets. We conclude that giant planet theory has a critical role in the interpretation of observation and emphasise the importance of advancing giant planet theory.

Simon Müller, Ravit Helled

Comments: 15 pages, 2 figures, accepted for publication in Frontiers in Astronomy and Space Sciences
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2304.12782 [astro-ph.EP] (or arXiv:2304.12782v1 [astro-ph.EP] for this version)
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Submission history
From: Simon Müller
[v1] Tue, 25 Apr 2023 13:05:13 UTC (316 KB)

SpaceRef co-founder, Explorers Club Fellow, ex-NASA, Away Teams, Journalist, Space & Astrobiology, Lapsed climber.