Berlin, Nov 14 : The NASA/ESA Hubble Space Telescope has taken the first visible light snapshot of a planet circling another star.
Estimated to be 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 Austrinus.
Fomalhaut has been a candidate for planet hunting ever since an excess of dust was discovered around the star in the early 1980s by the US- UK-Dutch Infrared Astronomy Satellite (IRAS).
In 2004, the coronagraph in the High Resolution Camera on Hubble's Advanced Camera for Surveys produced the first-ever resolved visible light image of a large dust belt surrounding Fomalhaut.
It clearly showed that this structure is in fact a ring of protoplanetary debris approximately 34.5 billion kilometers across with a sharp inner edge.
This large debris disk is similar to the Kuiper Belt, which encircles the solar system and contains a range of icy bodies from dust grains to objects the size of dwarf planets, such as Pluto.
Hubble astronomer Paul Kalas of the University of California, Berkeley (USA) and team members proposed in 2005 that the ring was being gravitationally modified by a planet lying between the star and the ring's inner edge.
Circumstantial evidence comes from Hubble's confirmation that the ring is offset from the centre of the star.
The sharp inner edge of the ring is also consistent with the presence of a planet that gravitationally "shepherds" ring particles. Independent researchers have subsequently reached similar conclusions.
Now, Hubble has actually photographed a point source of light lying 3 billion kilometers inside the ring's inner edge.
"Fomalhaut is the gift that keeps on giving. Following the unexpected discovery of its dust ring, we have now found an exoplanet at a location suggested by analysis of the dust ring's shape. The lesson for exoplanet hunters is 'follow the dust'," said team member Mark Clampin of NASA's Goddard Space Flight Center.
Observations taken 21 months apart by Hubble's Advanced Camera for Surveys coronagraph show that the object is moving along a path around the star, and so is gravitationally bound to it.
The planet is 17 billion kilometers from the star, or about 10 times the distance of the planet Saturn from the Sun.
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.