page_title: Fomalhaut
section_title: Debris disks and suspected planet
hierarchical_section_title: Fomalhaut / Fomalhaut A / Debris disks and suspected planet
caption_attribution_description: English: NASA's Hubble Reveals Rogue Planetary Orbit For Fomalhaut B01.08.13 http://www.nasa.gov/mission_pages/hubble/science/rogue-fomalhaut.html This false-color composite image, taken with the Hubble Space Telescope, reveals the orbital motion of the planet Fomalhaut b. Based on these observations, astronomers calculated that the planet is in a 2,000-year-long, highly elliptical orbit. The planet will appear to cross a vast belt of debris around the star roughly 20 years from now. If the planet's orbit lies in the same plane with the belt, icy and rocky debris in the belt could crash into the planet's atmosphere and produce various phenomena. The black circle at the center of the image blocks out the light from the bright star, allowing reflected light from the belt and planet to be photographed. The Hubble images were taken with the Space Telescope Imaging Spectrograph in 2010 and 2012. Credit: NASA, ESA, and P. Kalas (University of California, Berkeley and SETI Institute) Newly released NASA Hubble Space Telescope images of a vast debris disk encircling the nearby star Fomalhaut and a mysterious planet circling it may provide forensic evidence of a titanic planetary disruption in the system. Astronomers are surprised to find the debris belt is wider than previously known, spanning a section of space from 14 to nearly 20 billion miles (23 and 32 billion kilometers, respectively) from the star. Even more surprisingly, the latest Hubble images have allowed a team of astronomers to calculate the planet follows an unusual elliptical orbit that carries it on a potentially destructive path through the vast dust ring. The planet, called Fomalhaut b, swings as close to its star as 4.6 billion miles (7.4 billion kilometers or 49 AU), and the outermost point of its orbit is 27 billion miles (43 billion kilometers or 290 AU) away from the star. The orbit was recalculated from the newest Hubble observation made last year. "We are shocked. This is not what we expected," said Paul Kalas of the University of California at Berkeley and the SETI Institute in Mountain View, Calif. The Fomalhaut team led by Kalas considers this circumstantial evidence there may be other planet-like bodies in the system that gravitationally disturbed Fomalhaut b to place it in such a highly eccentric orbit. The team presented its finding Tuesday at the 221st meeting of the American Astronomical Society in Long Beach, Calif. Among several scenarios to explain Fomalhaut b's 2,000-year-long orbit is the hypothesis that an as yet undiscovered planet gravitationally ejected Fomalhaut b from a position closer to the star, and sent it flying in an orbit that extends beyond the dust belt. "Hot Jupiters get tossed through scattering events, where one planet goes in and one gets thrown out," said co-investigator Mark Clampin of NASA's Goddard Space Flight Center in Greenbelt, Md. "This could be the planet that gets thrown out." Hubble also found the dust and ice belt encircling the star Fomalhaut has an apparent gap slicing across the belt. This might have been carved by another undetected planet. Hubble's exquisite view of the dust belt shows irregularities that strongly motivate a search for other planets in the system. If its orbit lies in the same plane with the dust belt, then Fomalhaut b will intersect the belt around 2032 on the outbound leg of its orbit. During the crossing, icy and rocky debris in the belt could crash into the planet's atmosphere and create the type of cosmic fireworks seen when Comet Shoemaker-Levy 9 crashed into Jupiter. Most of the fireworks from collisions will be seen in infrared light. However, if Fomalhaut b is not co-planar with the belt, the only thing to be seen will be a gradual dimming of Fomalhaut b as it travels farther from the star. Kalas hypothesized that Fomalhaut b's extreme orbit is a major clue in explaining why the planet is unusually bright in visible light, but very dim in infrared light. It is possible the planet's optical brightness originates from a ring or shroud of dust around the planet, which reflects starlight. The dust would be rapidly produced by satellites orbiting the planet, which would suffer extreme erosion by impacts and gravitational stirring when Fomalhaut b enters into the planetary system after a millennium of deep freeze beyond the main belt. An analogy can be found by looking at Saturn, which has a tenuous, but very large dust ring produced when meteoroids hit the outer moon Phoebe. The team has also considered a different scenario where a hypothetical second dwarf planet suffered a catastrophic collision with Fomalhaut b. The collision scenario would explain why the star Fomalhaut has a narrow outer belt linked to an extreme planet. But in this case the belt is young, less than 10,000 years old, and it is difficult to produce energetic collisions far from the star in such young systems. Fomalhaut is a special system because it looks like scientists may have a snapshot of what our solar system was doing 4 billion years ago. The planetary architecture is being redrawn, the comet belts are evolving, and planets may be gaining and losing their moons. Astronomers will continue monitoring Fomalhaut b for decades to come because they may have a chance to observe a planet entering an icy debris belt that is like the Kuiper Belt at the fringe of our own solar system. For more information and for related images, please visit: http://www.nasa.gov/hubble and http://hubblesite.org/news/2013/01 RELEASE: 13-005 J.D. Harrington Headquarters, Washington 202-358-5241 j.d.harrington@nasa.gov Ray Villard Space Telescope Science Institute, Baltimore, Md. 410-338-4514 villard@stsci.edu
context_page_description: Fomalhaut, designation Alpha Piscis Austrini is the brightest star in the constellation of Piscis Austrinus, the "Southern Fish", and one of the brightest stars in the sky. It is a class A star on the main sequence approximately 25 light-years from the Sun as measured by the Hipparcos astrometry satellite. Since 1943, the spectrum of this star has served as one of the stable anchor points by which other stars are classified. It is classified as a Vega-like star that emits excess infrared radiation, indicating it is surrounded by a circumstellar disk. Fomalhaut, K-type main-sequence star TW Piscis Austrini, and M-type, red dwarf star LP 876-10 constitute a triple system, even though the companions are separated by approximately 8 degrees.
  Fomalhaut was the first stellar system with an extrasolar planet candidate imaged at visible wavelengths. Analysis of existing and new data suggests Fomalhaut b is not a planet, rather an expanding dust disk resulting from a former collision. The image was published in Science in November 2008. Fomalhaut is the third-brightest star known to have a planetary system, after the Sun and Pollux.
context_section_description: Fomalhaut is surrounded by several debris disks.
  The inner disk is a high-carbon small-grain (10–300 nm) ash disk, clustering at 0.1 AU from the star. Next is a disk of larger particles, with inner edge 0.4-1 AU of the star. The innermost disk is unexplained as yet.
  The outermost disk is at a radial distance of 133 AU (1.99×10¹⁰ km; 1.24×10¹⁰ mi), in a toroidal shape with a very sharp inner edge, all 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 outer 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 that disk. The mass of the planet, Fomalhaut b, was 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.
  Herschel Space Observatory images of Fomalhaut reveal that a large amount of fluffy micrometer-sized dust is present in the outer dust belt. Because such dust is expected to be blown out of the system by stellar radiation pressure on short timescales, its presence indicates a constant replenishment by collisions of planetesimals. The fluffy morphology of the grains suggests a cometary origin. The collision rate is estimated to be approximately 2000 kilometre-sized comets per day.
  Observations of the star's outer 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.
  If there are additional planets from 4 to 10 AU, they must be under 20 MJ; if from 2.5 outward, then 30 MJ.
caption: Debris ring around Fomalhaut showing location of Fomalhaut b—imaged by Hubble Space Telescope's coronagraph.
  (January 8, 2013) (NASA).
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