Fomalhaut - System

System

Fomalhaut is surrounded by a debris disk of dust in a toroidal shape with a very sharp inner edge at a radial distance of 133 AU (1.99×1010 km; 1.24×1010 mi), inclined 24 degrees from edge-on. The dust is distributed in a belt about 25 AU wide. The geometric center of the disk is offset by about 15 AU (2.2×109 km; 1.4×109 mi) from Fomalhaut. The disk is sometimes referred to as "Fomalhaut's Kuiper belt". Fomalhaut's dusty disk is believed to be protoplanetary, and emits considerable infrared radiation. Measurements of Fomalhaut's rotation indicate that the disk is located in the star's equatorial plane, as expected from theories of star and planet formation.

On November 13, 2008, astronomers announced an object, which they assumed to be an extrasolar planet, orbiting just inside the debris ring. This was the first extrasolar orbiting object to be seen with visible light, captured by the Hubble Space Telescope. A planet's existence had been previously suspected from the sharp, elliptical inner edge of Fomalhaut's debris disk. The mass of the planet, Fomalhaut b, is estimated to be no more than three times the mass of Jupiter but at least the mass of Neptune. There are indications that the orbit is not apsidally aligned with the dust disk, which may indicate that additional planets may be responsible for the dust disk's structure.

However M-band images taken from the MMT Observatory put strong limits on the existence of gas giants within 40 AU of the star and Spitzer Space Telescope imaging suggested that the object Fomalhaut b was more likely to be a dust cloud. In 2012, two independent studies confirmed that Fomalhaut b does exist; but it is shrouded by debris, so it may be a gravitationally-bound accumulation of rubble rather than a whole planet.

Observations of the star's dust ring by the Atacama Large Millimeter Array point to the existence of two planets in the system, neither one at the orbital radius proposed for the HST-discovered Fomalhaut b.