Hubble takes snapshot of Fomalhaut

The following sun and moon data for Nov. 20, 2008 is provided by the United States Naval Observatory.

Sunrise: 7:07 a.m.

Sunset: 4:50 p.m.

Moonrise: 11:50 a.m.

Moonset: 11:16 p.m.

Moon phase: The moon is waxing crescent with 39 percent of the visible disk illuminated. The moon is at First Quarter, Dec. 5 at 2:26 p.m. Mountain Standard Time.

NASA’s Hubble Space Telescope has taken the first visible-light snapshot of a planet circling another star.

Estimated at no more than three times Jupiter’s mass, the planet, called Fomalhaut b, orbits the bright southern star Fomalhaut, located 25 light-years away in the constellation Piscis Australis (the Southern Fish).

Fomalhaut has been a candidate for planet hunting ever since an excess of dust was discovered around the star in the early 1980s by NASA’s Infrared Astronomy Satellite (IRAS). Then, in 2004, equipment aboard the Hubble Space Telescope provided an astronomical breakthrough with the first-ever resolved visible-light image of the dust belt. The image clearly showed the structure as a ring of protoplanetary debris approximately 21.5 billion miles across with a sharp inner edge. Astronomers say the debris disk around Fomalhaut is analogous to the Kuiper Belt which encircles our solar system and contains a range of icy bodies from dust grains to objects the size of dwarf planets, such as Pluto.

In 2005, Hubble astronomer Paul Kalas, of the University of California at Berkeley, and team members proposed that the ring was being gravitationally modified by a planet lying between the star and the ring’s inner edge. The sharp inner edge of the ring is consistent with the presence of a planet that gravitationally “shepherds” ring particles. Independent researchers subsequently reached similar conclusions, and now, Hubble has photographed a point source of light lying 1.8 billion miles inside the ring’s inner edge.

“Our Hubble observations were incredibly demanding. Fomalhaut b is one billion times fainter than the star. We began this program in 2001, and our persistence finally paid off,” Kalas said.

Observations taken 21 months apart by Hubble’s Advanced Camera for Surveys coronagraph show the object is moving along a path around the star and therefore is gravitationally bound to it. The planet is 10.7 billion miles from the star, or about 10 times the distance of the planet Saturn from our sun.

Kalas and his team first used Hubble to photograph Fomalhaut in 2004, and made the unexpected discovery of its debris disk, which scatters Fomalhaut’s starlight. At the time they noted a few bright sources in the image as planet candidates. A follow-up image in 2006 showed that one of the objects is moving through space with Fomalhaut but changed position relative to the ring since the 2004 exposure.

Astronomers postulate that the planet may have formed at its location in a primordial circumstellar disk by gravitationally sweeping up remaining gas. Or, it may have migrated outward through a game of gravitational billiards where it exchanged momentum with smaller planetary bodies. It is commonly believed that Uranus and Neptune migrated out to their present orbits after forming closer to the sun and then gravitationally interacted with smaller bodies.

NASA’s James Webb Space Telescope, scheduled to launch in 2013, will be able to make coronagraphic observations of Fomalhaut in the near- and mid-infrared. The telescope will also be able to hunt for other planets in the system and probe the region inside the dust ring for structures such as an inner asteroid belt.

Viewing Fomalhaut

For backyard stargazers, Fomalhaut is visible deep in our southern sky around 7 p.m. The star, shining at magnitude 1.2 , should be easy to locate, as it is the brightest object in a relatively empty part of the night sky. Fomalhaut hovers at a position almost due south.

To reach Fomalhaut, draw an imaginary line southward along the right side of the Great Square of Pegasus to a point just a few degrees above the southern horizon. There stargazers should find Fomalhaut.

Photo courtesy NASA
This visible-light image from the Hubble Space Telescope shows the newly discovered planet, Fomalhaut b, orbiting its parent star. Estimated at no more than three times Jupiter’s mass, the planet, called Fomalhaut b, orbits the bright southern star Fomalhaut, located 25 light-years away in the constellation Piscis Australis (the Southern Fish). The discovery of Fomalhaut b marks another entry on the growing list of planets found far beyond the reaches of our own solar system.