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Hubble Catches Two Debris-Cloud Collisions at Fomalhaut, Recasting ‘Fomalhaut b’

A new Science study identifies the bright points as collision debris, prompting JWST follow-up.

An artist's rendition of a collision between two planetesimals in the debris disk around a young star. Collisions like these occur over hundreds of millions of years as gas and dust slowly coalesces into planets and moons.
Credit: Paul Kalas
Image
The Hubble Space Telescope observed the debris belt and dust clouds around the star Fomalhaut, which was blotted out to allow the fainter features around it to be seen.

Overview

  • Hubble images reveal transient dust clouds from impacts between asteroid-scale planetesimals in Fomalhaut’s debris belt, marking the first direct observation of such collisions beyond the Solar System.
  • The once-debated Fomalhaut b, now designated cs1, is confirmed as a fading dust cloud, while a second cloud, cs2, appeared in 2023 near the same ring.
  • Four independent analyses in the Dec. 18 peer-reviewed report converge on the collision explanation and map the clouds’ evolution.
  • Two detected events within roughly 20 years challenge models that predicted about one comparable collision per 100,000 years and point to a populous belt, with estimates near 300 million planetesimals.
  • Reported collider sizes span tens of kilometers (about 30–60 km), and approved JWST NIRCam observations will probe dust color and composition as Hubble’s monitoring is constrained by a 2024 gyro failure.