Fomalhaut

A Second Planetesimal Collision In The Fomalhaut System

By Keith Cowing

Press Release

NASA

December 22, 2025

Filed under exoplanet, Fomalhaut, Fomalhaut b, Hubble, NASA, Planetesimal, protoplanetary disk. astronomy

A Second Planetesimal Collision In The Fomalhaut System — Optical images of the Fomalhaut system in 2012 and 2023. Both panels are white light HST/STIS images. The bright central star has been artificially eclipsed with a coronagraph, to reveal the fainter belt-like dust structure around the star, with intensity indicated by the color bar. Black regions have no data, due to the coronagraph and the limited field of view of the camera. (A) Fom cs1 (white arrow) in our re-reduction of the 2012 observation (12). No other point sources are detected inside the dust belt. (B) Fom cs2 (white arrow) in the September 2023 observation, located northwest of the star at the inner edge of the dust belt. There is no conclusive evidence of Fom cs1 in 2023. In both panels, the inset boxes magnify a 1” × 1” (7.7 × 7.7 au) region centered on the identified point sources. All other point-like or extended sources in the field are known background stars or galaxies. — NASA via Science

The nearby star Fomalhaut is orbited by a compact source, Fomalhaut b, which has previously been interpreted as either a dust-enshrouded exoplanet or a dust cloud generated by the collision of two planetesimals.

Such collisions are rarely observed but their debris can appear in direct imaging. We report Hubble Space Telescope observations that show the appearance in 2023 of a second point source around Fomalhaut, resembling the appearance of Fomalhaut b twenty years earlier.

We interpret this additional source as a dust cloud produced by a recent impact between two planetesimals. The positions and motion of two impact-generated dust clouds over twenty years provide constraints on the collisional dynamics in the debris belt.

Composite image of the 2012, 2013, and 2023 observations. The white light STIS images from three epochs have been averaged (intensity indicated by the color bar) to show the relative positions of cs1 and cs2 (white labels) a decade apart. Fom cs1 appears as a linear radial feature because its position moved between 2012 and 2013. The white scale bar is 5” (38.5 au). The data have been smoothed with a 0.8 pixel Gaussian filter. The dust belt is brighter to the east (left) because the dust grains have an asymmetric scattering phase function. — NASA via Science

Comments: Published online in Science First Release on December 18, 2025. 32 pgs, 15 figs, 6 tables. This is the author’s version of the work. It is posted here by permission of the AAAS for personal use, not for redistribution

Paul Kalas, Jason J. Wang, Maxwell A. Millar-Blanchaer, Bin B. Ren, Mark C. Wyatt, Grant M. Kennedy, Maximilian Sommer, Thomas M. Esposito, Robert J. De Rosa, Michael Fitzgerald

Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2512.15861 [astro-ph.EP] (or arXiv:2512.15861v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2512.15861
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Journal reference: P. Kalas et al., Science 10.1126/science.adu6266 (2025)
Related DOI:
https://doi.org/10.1126/science.adu6266
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Submission history
From: Paul Kalas
[v1] Wed, 17 Dec 2025 19:00:02 UTC (3,606 KB)
https://arxiv.org/abs/2512.15861

Astrobiology, Astrogeology,

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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