Artist's impression of a Jupiter-sized planet orbiting the nearby star Epsilon Eridani. The recently confirmed planet is in fact 1.5 times Jupiter's size and orbits in a disc of dust.
Credit: G. Bacon/NASA
SYDNEY: It's official: planets are formed from the debris swirling around a young star, astronomers have confimed, more than 250 years after the idea was first proposed.
In 1755, the philosopher Emmanuel Kant first proposed that planets are born from discs of dust and gas orbiting their home stars. Though astronomers have detected more than 200 extrasolar planets and have seen many debris disks around young stars, they had never observed a planet and a debris disc around the same star. Now, the NASA/ESA Hubble Space Telescope, in collaboration with ground-based observatories, has at last confirmed what Kant and scientists have long predicted.
The results, due to appear in the November issue of the Astronomical Journal, found that an object orbiting the nearby Sun-like star Epsilon Eridani in a disc of dust was definitely a planet.
"Because of Hubble, we know for sure that it is a planet and not a failed star," project leader, Barbara McArthur of the University of Texas, said. If it had been larger, it could have been a brown dwarf, which would not have confirmed any link between planets and stellar dust.
Epsilon Eridani is located 10.5 light-years from Earth in the constellation Eridanus. The star is familiar to Star Trek fans as the solar system of the planet Vulcan, home world of the character, Mr Spock.
The planets in our Solar System share a common alignment, evidence that they were created at the same time in the Sun's disc. But the Sun is a middle-aged star - 4.5 billion years old - and its debris disc dissipated long ago. Epsilon Eridani, however, still retains its disc because it is young, only 800 million years old.
The planet's orbit is inclined 30 degrees to Earth, the same angle at which the star's disc is tilted.
The planet's true mass, the key to describing the object as a planet, is 1.5 times Jupiter's mass. The planet, called Epsilon Eridani b, is the nearest extrasolar planet to Earth. It orbits its star every 6.9 years.
Although Hubble and other telescopes cannot image the gas giant planet now, they may be able to snap pictures of it in 2007, when its orbit is closest to Epsilon Eridani. The planet may be bright enough in reflected sunlight to be imaged by Hubble, other space-based cameras, and large ground-based telescopes.
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