Facts about Fomalhaut b and Fomalhaut
Fomalhaut b is an extrasolar planet approximately 25 light-years away in the constellation of Piscis Austrinus. The planet was discovered orbiting the A-type main sequence star Fomalhaut in 2008 in photos taken by the Hubble Space Telescope. Fomalhaut b was one of the first extrasolar planets whose orbital motion was confirmed via direct imaging.
Discovery
Fomalhaut b is the first exoplanet observed directly in visible light, the first imaged planet since Neptune to have been predicted prior to discovery, and the first planet to have been correctly predicted based on its interaction with a debris disk. It is also believed to be the coolest, lowest-mass object ever imaged outside our own solar system.
The existence of the planet was inferred in 2005 from its influence on the Fomalhaut dust belt; the belt is not centered on the star, and has a sharper inner boundary than would normally be expected. However, the planet was only located in May 2008 after Paul Kalas singled it out of Hubble photographs taken in 2004 and 2006. NASA released the composite discovery photograph, obtained by the Hubble Space Telescope's ACS, on November 13, 2008. In the image, the bright outer oval band is the dust ring, while the features inside of this band represent noise from scattered starlight.
Kalas remarked, "It’s a profound and overwhelming experience to lay eyes on a planet never before seen. I nearly had a heart attack at the end of May when I confirmed that Fomalhaut b orbits its parent star."
Physical Characteristics
The planet is estimated to be approximately the same size as Jupiter, with a maximum mass of three Jupiters and a most probable mass of 0.5 to two. It is 115 AU (17 billion km, 11 billion mi, about 20% greater than the aphelion distance of Eris and 3.8 times the semi-major axis of Neptune) from its sun, giving it an orbital period of 872 earth years. Fomalhaut has about 16 times the Sun's luminosity, so Neptune and Fomalhaut b are in regions of similar temperature.
Fomalhaut b is suspected, on the basis of its brightness in visible light and dimness in infrared, to be surrounded by a circumplanetary disc with a radius approximately 20–40 times the radius of Jupiter (by comparison, the outer edge of Saturn's A ring is at a distance of only about 2 Jupiter radii from the center of the planet). This size is similar to the orbital radii of Jupiter's Galilean satellites and therefore may represent a stage in the formation of a system of moons around the planet.
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