The Hubble Space Telescope has snapped the first visible-light picture of a planet outside the Solar System. Although so-called “extrasolar” planets have been found before – 300 had at the last count – this is the first time we have been able to view one directly. Previous discoveries were made using indirect methods such as radial-velocity surveys which search for stars that “wobble” due to their planets.
The new planet, called Fomalhaut b, is suspected to be more than three times the mass of Jupiter. It orbits the star Fomalhaut, 25 light-years away in the constellation Piscis Australis, which is surrounded by a huge cloud of dust similar to the Kuiper Belt around our own sun.
This debris disk was discovered when Hubble took a picture of the star in 2004. Astronomer Paul Kalas, of the University of California at Berkeley suspected in 2005 that the dust was being gravitationally modified by a planet lying between the star and the ring’s inner edge.
Kalas and his team’s suspicions have finally paid off now that Hubble has photographed a point 1.8 billion miles inside the ring’s inner edge. Taking the picture was no mean feat however.
“Our Hubble observations were incredibly demanding. Fomalhaut b is 1 billion times fainter than the star. We began this program in 2001, and our persistence finally paid off,” Kalas says.
“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,’” added team member Mark Clampin of NASA’s Goddard Space Flight Center in Greenbelt, Md.
A second observation of Fomalhaut in 2006 was used to confirm the planet’s existence. By noting the difference between the two photos, the team were able to calculate a 872-year-long orbit for the planet. By comparison, Pluto only takes 248 years to orbit the sun.
Scientists will be keeping their eye on Fomalhaut b for a while yet. Future observations will attempt to view the planet using infrared light and look for evidence of water vapour in the atmosphere. This and other observations will be made possible by the launch of NASA’s James Webb Space Telescope. The replacement for Hubble is scheduled to launch in 2013.