Discovery Of An Exterior Third Planet Orbiting β Pictoris

by Keith CowingJuly 2, 2026July 2, 2026

$β Pic d possible orbits and stability fractions. Left: Allowed orbits (pink) from Octofitter (W. Thompson et al. 2023) posteriors fit to astrometry and planetary RV (black) reported in Table 1, projected on-sky. Possible orbits are also shown in RV space. The locations of β Pic b and the approximate inner edge of the debris disk are plotted for reference. β Pic c is not shown as it falls nearly coincident with the star. Right: Fraction of stable orbits as a function of β Pic d mass and semi-major axis, as determined by the MEGNO chaos indicator from orbit posteriors integrated over 5 Myr. The semi-major axis range of the 68% percentile orbit posteriors is overlaid in pink. Orbital period ratios with β Pic b are shown as white dashed lines. The pink shaded region represents the 68th percentile of the orbital posteriors. The current astrometric baseline and RV precision do not strongly constrain the orbit; however, stability requirements suggest a semi-major axis of > 30 au. -- astro-ph.EP$

β Pic d possible orbits and stability fractions. Left: Allowed orbits (pink) from Octofitter (W. Thompson et al. 2023) posteriors fit to astrometry and planetary RV (black) reported in Table 1, projected on-sky. Possible orbits are also shown in RV space. The locations of β Pic b and the approximate inner edge of the debris disk are plotted for reference. β Pic c is not shown as it falls nearly coincident with the star. Right: Fraction of stable orbits as a function of β Pic d mass and semi-major axis, as determined by the MEGNO chaos indicator from orbit posteriors integrated over 5 Myr. The semi-major axis range of the 68% percentile orbit posteriors is overlaid in pink. Orbital period ratios with β Pic b are shown as white dashed lines. The pink shaded region represents the 68th percentile of the orbital posteriors. The current astrometric baseline and RV precision do not strongly constrain the orbit; however, stability requirements suggest a semi-major axis of > 30 au. -- astro-ph.EP

[astro-ph.EP] We report the discovery of β Pictoris d (β Pic d), a third giant planet in the β Pictoris system, which now becomes only the second directly imaged system with more than two confirmed planets. β 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 CH₄, CO, and H₂O absorption features, and β 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 β Pic d being responsible for carving the inner edge of the β 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. β 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.

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

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
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2606.23789 [astro-ph.EP] (or arXiv:2606.23789v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2606.23789
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Submission history
From: Aidan Gibbs
[v1] Mon, 22 Jun 2026 18:00:02 UTC (2,785 KB)
https://arxiv.org/abs/2606.23789

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... More by Keith Cowing