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Exoplanetary Scratchpad

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Fomalhaut is also known as Piscis Austrini, 24 Piscis Austrini, Gl 881, HD 216956, and HR 8728. A triple star, the second brightest star known to have exoplanets. Star A is a white main sequence star about twice the Sun's mass and somewhat less than twice its radius. It was originally thought to be about 200 million years old, but now thought to be 400 MYO, and will turn into a giant in about a billion years. Its dust disk is observed in unprecedented detail. It appears reminiscent of the "Eye of Sauron" from the Lord of the Rings films. A planet suspected of causing a sharp gap in the ring was suspected and imaged, becoming the first visually detected and the first planet since Neptune to be predicted prior to its discovery. The planet, Dagon, orbits about 115 AU and is between Neptune and 3x Jupiter's mass in an eccentric orbit. Planet b was shown to deviate slightly from its predicted path, stirring up some controversy about the planets' existence. The Hubble instrument that detected it is damaged and will not be fixed, making it unobservable for a time. Later analysis of old Hubble data confirmed its existence. Material surrounding the planet has been imaged, rather than the planet itself, which its discoverers admit takes it off the directly imaged list. The planet is hurdling outward from the star in a highly elongated path and will encounter the inner edge of the outer belt in 2032, where icy debris will smash into its atmosphere (unless its orbit is highly inclined). No heat has been detected from the planet, which suggests it is sub-Jovian in mass and could be as small as Pluto, though this could be explained by dissipation from surrounding dust. Evidence for another planet "slicing" through the dust disk was also found, and it may have been responsible for planet b's elliptical orbit. The shape of the ring was put into focus by ALMA, 140 AU out, 16 AU wide, and 1/7th AU thick, placing limits on proposed shepherding exoplanets and showing them to be quite small (a couple times larger than Mars), perhaps why they weren't detected visually. Mapping by ALMA was completed later on and shows the first "apocenter glow", where dust particles clump around slower moving and further out parts of their elliptical orbit. Some proposed inner planets via effects of debris disk could be better interpreted as gas produced effects. The ring is believed to be continuously replenished by cometary collisions occurring every day. An estimated 260 Billion to 83 Trillion comets could exist in it, equivalent to what is in the Sun's Oort Cloud. Star B, an orange dwarf 0.91 ly away has no known disk. Star C, a recently identified Red Dwarf member of the system, located extremely far from the primary (2.5 ly), was also found to have its own disk. Previous interactions may have tilted Star A's disk. The star is a part of the Castor Moving Group. One of the first 20 exoplanet systems allowed to be given common names by the IAU. The planet is named after a half fish Semitic god.

My Thoughts[]

Man, I wish you could see this star in the northern hemisphere. Guess I have to settle for Pollux when it's winter. The discoverer wanted this to be named after a dream or something, since there was a lot of evidence stacked against its existence for a while. But I guess we can put the doubt to rest since it's gonna be named now. It's pretty interesting that only clumps around it are visible. It could be a small planet.


Well, it's name means Mouth of the Fish. It's star system is nicknamed "eye of sauron". It marked summer solsist in 2500 bc. Its discoverer was born in Crete and suggested it be named after a dream related thing.

  • Labroides - Fomalhaut=Mouth of large fish - Labroides=Small fish to clean the mouth of large fish


  • ichtus - The ichtus or ichthys (Greek ΙΧΘΥΣ , [' ix.θys ] "fish" ) is a symbol consisting of two intersecting arcs form that looks like the profile of a fish, the fish is also interpreted from the archetypal psychology symbol of the profound truth ( underwater) that is hidden to be caught and then come out . Shining in secret at first , and the fisherman must get to feed.

nice, but its religious nature would probably turn the IAU off

Fomalhaut System Web Pages[]

Fomalhaut System In the News[]

Disk Discovered by IRAS (1983)[]

Disk First Imaged by JAC (1998)[]

Age Determined (1998)[]


Resonant Patterns Detected in Ring (2000)[]


Warp in Ring Found with SCUBA - Planet Announced (2002)[]

Ring Imaged by Spitzer (2003)[]

Ring Imaged by Hubble (2005)[]

Neptunian May Be Responsible For Ring Assymetry (2007)[] Extrasolar Vision Thread

Mini-Planet Embros Detected (Oct 2007)[]

Planet Imaged by Hubbel(Nov 2008)[]

Perhaps These Are the Only Exoplanets Imaged (2009)[]

Feature Article on Imaged Planets (2011)[]

See Imaged Exoplanets for more systems

Controversy Around System (Sep 2011)[]

Planet Could be Just a Dust Cloud (Jan 2012)[]

Planet Could be Lava World (Feb 2012)[]

Dust Disk Continuously Recreated by Cometary Collisions Each Day (Apr 2012)[]

ALMA Indicates Any "Shepherd Planets" Would Be Small (Apr 2012)[]

Dust Ring and Planet Could be Asteroid Collision Debris (Apr 2012)[]

Hubble to Seek Confirmation of Planet (Apr 2012)[]

Planet Vindicated (Oct 2012)[]

Planet's Orbit is Very Eccentric (Jan 2013)[]

Vega Found to be More Similar to Fomalhaut (Jan 2013)[]

Recap on Planet's Confirmation (Jan 2013)[]

Gas Could Explain Patterns in Disk (Jul 2013)[]

See also TW Hydrae System

Comet Disk Found Around Star C (Dec 2013)[]

One of the Top 20 Exoplanetary Systems First Up For Naming (May 2015)[]

Ring Image Completed (May 2017)[]

See Also[]