Discovery of an Exterior Third Planet Orbiting beta Pictoris

arXiv:2606.23789 · astro-ph.EP · Submitted 2026-06-22 · Read on arXiv

Aidan Gibbs, Jean-Baptiste Ruffio, Alexis Bidot, Travis S. Barman, Clarissa R. Do Ó, Quinn M. Konopacky, Marshall D. Perrin, Aneesh Baburaj, Beck Dacus, Bruce Macintosh, Alexander B. Madurowicz, Jerry W. Xuan

astro-ph.EP

Submitted: 2026-06-22

Comments: 14 pages, 4 figures, accepted for publication in ApJ Letters, this article is embargoed for discussion in the press until formal publication in ApJ Letters; press releases are pending

License: http://creativecommons.org/licenses/by/4.0/

The gist: We report the discovery of beta Pictoris d (beta Pic d), a third giant planet in the beta Pictoris system, which now becomes only the second directly imaged system with more than two confirmed

Terminology

Abstract

We report the discovery of beta Pictoris d (beta Pic d), a third giant planet in the beta Pictoris system, which now becomes only the second directly imaged system with more than two confirmed planets. beta Pic d was serendipitously detected in JWST/NIRSpec IFU observations. A second epoch of NIRSpec and MIRI/MRS observations confirm the initial discovery. The extracted spectrum shows clear CH 4, CO, and H 2 O absorption features, and beta Pic d's measured radial velocity is consistent with its orbital position. Radial velocity and astrometry measurements combined with orbital stability simulations suggest a semi-major axis > 30 au, consistent with beta Pic d being responsible for carving the inner edge of the beta Pictoris debris disk. Using effective temperature estimates from atmosphere model grid fits combined with evolutionary models, we estimate a mass of 2--4 M Jup. beta Pic d is the first planet discovered using spectral template matching with moderate-resolution spectroscopy, highlighting its sensitivity to planetary molecular features hidden within bright extrasolar debris disks that are difficult to access with broadband imaging.

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