First photographs of planets outside solar system released
15 Nov 2008
For quite some time, astronomers have reported the existence of planets outside our solar system. These had been detected by gravitational perturbations caused by them on adjoining planetary bodies, like the stars they are revolving around. However, photographic evidence was missing. Not any more.
The first pictures of extra-solar planets have now been taken, two groups report in the journal Science. Visible and infrared images have been snapped of a planet orbiting a star 25 light-years away. The planet is believed to be the coolest, lowest-mass object ever seen outside our own solar neighbourhood.
In a separate study, an exoplanetary system, comprising three planets, has been directly imaged, circling a star in the constellation Pegasus. None of the aforementioned four planets are remotely habitable or remotely like Earth. But they raise the possibility of others more hospitable.
It's only a matter of time before "we get a dot that's blue and Earthlike," said astronomer Bruce Macintosh of the Lawrence Livermore National Lab. He led one of the two teams of photographers. "It is a step on that road to understand if there are other planets like Earth and potentially life out there," he added.
Macintosh's team used two ground-based telescopes, while the second team relied on photos from the 18-year-old Hubble Space Telescope to gather images of the exoplanets - planets that don't circle our sun. The research from both teams was published in Thursday's online edition of the journal Science.
The first team used the Keck and Gemini telescopes in Hawaii to look near a star called HR 8799, which is just visible to the naked eye. The team studied light in the infrared part of the spectrum, hoping to spot planets that were still hot from their formation. What they found in 2004, and confirmed again this year, are three planets circling the star.
According to a theoretical model that accounts for the light coming from the planets, they range in size from five to 13 times the mass of Jupiter and are probably only about 60 million years old.
Paul Kalas of the University of California, Berkeley, led the second team that used the Hubble Space Telescope to image the region around a star called Fomalhaut in the constellation Piscis Austrinus.
The team estimates that the planet it discovered, designated Fomalhaut b, is some 18 billion kilometres away from its star, about as massive as Jupiter and completes an orbit in about 870 years. It may also have a ring around it.
"I nearly had a heart attack at the end of May when I confirmed that Fomalhaut b orbits its parent star," Kalas said. "It's a profound and overwhelming experience to lay eyes on a planet never before seen."
In the past 13 years, scientists have discovered more than 300 planets outside our solar system, but they have done so indirectly, by measuring changes in gravity, speed or light around stars. The difficulty for astronomers imaging exoplanets is that their parent star's light swamps them - like trying to spot a match next to a floodlight at a distance of a mile.
But advances in optics and image processing have allowed astronomers to effectively subtract the bright light from stars, leaving behind light from the planets. That light can either come in the infrared, caused by the planets' heat, or be reflected starlight.
