Brussels, 18 Dec 2003
UK astronomers have produced a compelling case that Vega, one of the brightest stars in the sky, has a planetary system around it more like our own solar system than anything discovered so far.
Until now, all of the hundred or so planets discovered around neighbouring stars have been huge gaseous masses orbiting close to their star – nothing like our own solar system. Researchers at the UK Astronomy Centre of the Royal Observatory Edinburgh (UK) developed new computer modelling techniques which show a faint dusty disk around Vega.
In terms of our own planetary system, this disk has a similar orbit to Neptune's. Given the wide orbit of the Neptune-like planet, there is plenty of room in between for small rocky planets similar to the earth to have formed – the 'Holy Grail' for astronomers wanting to know whether we are alone in the universe.
Mark Wyatt, author of a paper about the discovery which appeared recently in The Astrophysical Journal, says the irregular shape of the disk is the clue that it is likely to contain planets. "Although we can't directly observe the planets, they have created clumps in the disk of dust around the star," he confirms.
Fifth brightest star from the…
The modelling technique is based on observations taken with the world's most sensitive submillimetre camera, SCUBA. The camera, built in Scotland, is operated on the James Clerk Maxwell Telescope in Hawaii and shows images of a disk of very cold dust (-180°C) in orbit around Vega, the fifth brightest star in the night sky.
The modelling suggests that the Neptune-like planet actually formed much closer to the star than its current position. Over about 56 million years, its orbit widened, gradually sweeping comets out with it and giving the 'dust disk' its clumpy appearance. Wyatt says the same process is thought to have happened to the earth's solar system. "Neptune was 'pushed' away from the sun because of the presence of Jupiter orbiting inside it," he explains.
The model can be tested in two ways. Wayne Holland, who made the original observations, explains: "The model predicts that the clumps in the disk will rotate around the star once every three hundred years. If we take more observations after a gap of a few years we should see the movement of the clumps. Also the model predicts the finer detail of the disk's 'clumpiness' which can be confirmed using the next generation of telescopes and cameras."
Ironically, the star barely appears in the SCUBA image because – being 58 times brighter than our sun – it is far too hot to be seen with this kind of detector. Vega is, however, easily seen with the naked eye. It is the third brightest star visible from Northern latitudes and is bluish-white in colour.
Not surprisingly, Vega was also the first star ever to be photographed in 1850. The historic picture was taken at Harvard Observatory using a 15-inch refractor telescope during a 100 second exposure.