Fomalhaut debris ring
The Fomalhaut debris ring - a strikingly narrow, off-centre band of dust and ice about 140 AU from Fomalhaut, tilted so we see it as a wide ellipse (the 'Eye of Sauron'). Its sharp inner edge and eccentric shape suggest sculpting by unseen planets. JWST revealed it is actually a set of nested belts.
Science
Classification
- Type
- Collisional debris disk (a dust ring)
- What it is
- Rocky and icy debris left over from planet formation, ground to dust by collisions among unseen comets and asteroids — NOT a gas/protoplanetary disk
- Analogue
- The Solar System's Kuiper Belt and asteroid belt
What a debris disk tells us
- Collisional cascade
- Starlight removes small dust grains quickly, so the dust we see must be freshly made — evidence of colliding planetesimals we cannot see directly
- Hidden planets
- Sharp edges, gaps or narrow rings are often shepherded by the gravity of an unseen planet — a clue to worlds not yet detected
How we know
- Note
- Debris disks are real, detected structures — first from the infrared 'excess' their dust radiates, and directly imaged in sub-millimetre light where resolved. Fine structure is often model-based rather than directly pictured; this card shows the established belt, never fabricated detail.
Discovery & history
- Discovered
- January 1, 2005
- By
- P. Kalas et al. (Hubble)
- Method
- Infrared excess (space telescope)
- Name
- Not a formally named object - the debris ring of Fomalhaut (Alpha Piscis Austrini), nicknamed the 'Eye of Sauron'.
The ring was imaged in 2005 by Hubble (Kalas et al.), its knife-sharp edge hinting at a shepherding planet. A bright point inside it, announced in 2008 as the planet 'Fomalhaut b', later faded and expanded - by 2020 it was understood as an expanding dust cloud from a collision of icy planetesimals, not a planet. In 2023 JWST resolved the system into an inner disk, an intermediate belt and the famous outer ring.
Images
Images from open archives · credit shown per image