US:The world's leading team of planet-hunters has announced the discovery of 28 new planets outside our solar system.
They are among 37 objects outside our solar system that have been found to orbit distant stars. Seven of the objects are confirmed brown dwarfs - failed stars much more massive than the largest planet - and two are borderline and could be small brown dwarfs or large planets.
Dr Jason Wright of the University of California announced the team's results yesterday at the annual meeting of the American Astronomical Society in Honolulu.
"Taken together, in the last year our teams have increased the number of known planets by 12 per cent and shown that at least 30 per cent of stars known to host planets have more than one object orbiting."
He said his team's success was a testament to the advances in observing technology. "Planet hunting is getting much more sophisticated. Our primary technique - observing the small, reflex motions of a star as a planet orbits it - has improved greatly in the past 15 years. Today we can detect changes in the motion of some stars of only one metre per second."
Scientists were getting to the stage that, if they were observing our own solar system from afar, their telescopes could detect Jupiter. They have recorded more than 200 planets outside our solar system.
One of the highlights is a detailed analysis of a planet circling the star Gliese 436, 30 light years from earth. Working with colleagues in Europe, Dr Wright's team calculated that the planet was an ice giant of at least 22 earth masses, which makes it slightly more massive than Neptune.
"From the density of two grams per cubic centimetre - twice that of water - it must be 50 per cent rock and about 50 per cent water, with perhaps small amounts of hydrogen and helium," said Dr Geoff Marcy, who leads the university's research group.
"So this planet has the interior structure of a hybrid super-earth/Neptune, with a rocky core surrounded by a significant amount of water compressed into solid form at high pressures and temperatures."
The planet's 2.6-day orbit means it is very close to the star, making it a hot Neptune.
Dr Wright said this was the first planet outside the solar system for which astronomers could infer the presence of water with near certainty, but he cast doubt on the idea that there was life there.
"These planets, like most of the giant planets in our solar system, will probably have no solid surface," he said. - (Guardian service)