Alpha Centauri

Worlds Next Door: A Candidate Giant Planet Imaged in the Habitable Zone of α Cen A. I. Observations, Orbital and Physical Properties, and Exozodi Upper Limits

By Keith Cowing

Status Report

astro-ph.EP

August 7, 2025

Filed under Alpha Centauri A, astro-ph.EP, astronomy, exoplanet, exozodiacal dust, Habitable Zone, imaging, JWST

Worlds Next Door: A Candidate Giant Planet Imaged in the Habitable Zone of α Cen A. I. Observations, Orbital and Physical Properties, and Exozodi Upper Limits — JWST’s view of the α Cen AB system. Shown above is a background-subtracted Stage 2b F1550C image of the α Cen AB system from August 2024. The image is oriented North up and East left. The white stars denote the approximate positions of α Cen B, saturated near the top of the image, and α Cen A in the lower part of the image hidden behind the F1550C mask. The right colorbar (logarithmically scaled) is associated with this image. At the edge of the detector, to the West of α Cen A, is a known background source KS5 (Kervella et al. 2016). To the East of α Cen A is known background source KS2 (Kervella et al. 2016), shown as an inset, as it is only detected after performing PSF subtraction (no colorbar shown for the inset, scaled linearly between −5 and 50 MJy/sr). An ≈2. ′′75 radius region around α Cen A is shaded and mapped to three PSF-subtracted images, one for each observation epoch. Candidate S1 is seen only in August 2024. The bottom colorbar (linearly scaled) is associated with the three PSF-subtracted images. For reference, 1 MJy/sr ≈ 4.6 × 10−6 Jy/AiryCore, where AiryCore is defined as the area of a circular aperture of diameter 1 FWHM (≈ 0. ′′5). — astro-ph.EP

We report on coronagraphic observations of the nearest solar-type star, α Cen A, using the MIRI instrument on the James Webb Space Telescope.

With three epochs of observation (August 2024, February 2025, and April 2025), we achieve a sensitivity sufficient to detect T_eff≈ 225-250 K (1-1.2 R_Jup) planets between 1″-2″ and exozodiacal dust emission at the level of >5-8× the brightness of our own zodiacal cloud. The lack of exozodiacal dust emission sets an unprecedented limit of a few times the brightness of our own zodiacal cloud−a factor of ≳10 more sensitive than measured toward any other stellar system to date.

In August 2024, we detected a Fν(15.5 μm) = 3.5 m_Jy point source, called S1, at a separation of 1.5″ from α Cen A. Because the August 2024 epoch had only one successful observation at a single roll angle, it is not possible to unambiguously confirm S1 as a bona fide planet.

Our analysis confirms that S1 is neither a background nor a foreground object. S1 is not recovered in the February and April 2025 epochs. However, if S1 is the counterpart of the object, C1, seen by the VLT/NEAR program in 2019, we find that there is a 52% chance that the S1+C1 candidate was missed in both follow-up JWST/MIRI observations due to orbital motion.

Incorporating constraints from the non-detections, we obtain families of dynamically stable orbits for S1+C1 with periods between 2-3 years. These suggest that the planet candidate is on an eccentric (e≈0.4) orbit significantly inclined with respect to α Cen AB orbital plane (i_mutual≈50^∘, or ≈130^∘).

Based on the photometry and orbital properties, the planet candidate could have a temperature of 225 K, a radius of ≈1-1.1 R_Jup and a mass between 90-150 M_Earth, consistent with RV limits.

Charles Beichman, Aniket Sanghi, Dimitri Mawet, Pierre Kervella, Kevin Wagner, Billy Quarles, Jack J. Lissauer, Max Sommer, Mark Wyatt, Nicolas Godoy, William O. Balmer, Laurent Pueyo, Jorge Llop-Sayson, Jonathan Aguilar, Rachel Akeson, Ruslan Belikov, Anthony Boccaletti, Elodie Choquet, Edward Fomalont, Thomas Henning, Dean Hines, Renyu Hu, Pierre-Olivier Lagage, Jarron Leisenring, James Mang, Michael Ressler, Eugene Serabyn, Pascal Tremblin, Marie Ygouf, Mantas Zilinskas

Comments: Accepted to ApJL. 34 pages, 22 figures, 10 tables
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)
Cite as: arXiv:2508.03814 [astro-ph.EP] (or arXiv:2508.03814v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2508.03814
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Submission history
From: Aniket Sanghi
[v1] Tue, 5 Aug 2025 18:01:46 UTC (10,437 KB)
https://arxiv.org/abs/2508.03814

Astrobiology, exoplanet,

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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