Electromagnetism

Detecting And Characterising The Magnetic Field Of Exoplanets

By Keith Cowing

Status Report

astro-ph.IM

July 7, 2025

Filed under astro-ph.IM, exoplanet, habitability, Habitable Worlds Observatory, magnetic field, Spectropolarimetry

Detecting And Characterising The Magnetic Field Of Exoplanets — Left: The known exoplanet population (divided into two bins of masses above and below 10 Earth masses) as a function of their semi-major axis and of the central stellar mass. The classical habitable zone is shown by the blue area, and the region where star-planet magnetic interactions (SPMI) are expected to occur is shown by the red area, i.e. within the so-called Alfven surface. Right: Modelling of the wind of HD 189733 based on a spectropolarimetric map ( ´ Fares et al. 2017) showing the magnetic connectivity between the hot Jupiter HD 189733 b and its host (from Strugarek et al. 2022). — astro-ph.IM

Magnetic fields play a crucial role in planetary evolution and habitability. While the intrinsic magnetic fields of solar system planets are relatively well understood, the magnetic properties of exoplanets remain largely unconstrained, despite their potential ubiquity.

Detecting exoplanetary magnetic fields is essential to advancing our understanding of planetary habitability beyond the solar system. This paper focuses on two promising spectropolarimetric techniques for detecting magnetic fields in hot exoplanets: direct detection through polarization signatures in the He I 1083 nm triplet and indirect detection via star-planet magnetic interactions manifesting as stellar hot spots. The direct method is particularly suited to close-in gas giants, leveraging the Hanle and Zeeman effects to detect low-amplitude magnetic fields.

The indirect method can apply to both giant and low-mass planets by identifying magnetic connectivity-induced features in the stellar atmosphere. Although the interpretation of current detections remain tentative, upcoming high-resolution spectropolarimetric capabilities in the UV and near-infrared, particularly with future missions like HWO, promise to enable definitive measurements of exoplanetary magnetic fields.

These advancements will open new avenues for probing the magnetic environments of exoplanets and their implications for atmospheric retention and habitability.

A. Strugarek, S. V. Berdyugina, V. Bourrier, J. A. Caballero, J. J. Chebly, R. Fares, A. Fludra, L. Fossati, A. García Muñoz, L. Gkouvelis, C. Gourvès, J. L. Grenfell, R. D. Kavanagh, K. G. Kislyakova, L. Lamy, A. F. Lanza, C. Moutou, D. Nandy, C. Neiner, A. Oklopčić, A. Paul, V. Réville, D. Rodgers-Lee, E. L. Shkolnik, J. D. Turner, A. A. Vidotto, F. Yang, P. Zarka

Comments: 9 pages, 2 figures, 5 tables, Towards the Habitable Worlds Observatory: Visionary Science and Transformational Technology SCDD, to be presented at HWO2025 and submitted to Astronomical Society of the Pacific
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)
Cite as: arXiv:2507.02010 [astro-ph.IM] (or arXiv:2507.02010v1 [astro-ph.IM] for this version)
https://doi.org/10.48550/arXiv.2507.02010
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Submission history
From: Antoine Strugarek
[v1] Wed, 2 Jul 2025 06:45:05 UTC (2,066 KB)
https://arxiv.org/abs/2507.02010
Astrobiology

Keith Cowing

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻

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