LONDON - Scientists trying to connect the dots that make up the universe filled in key pieces of the puzzle Monday, announcing the discovery of nine new planets that orbit stars outside our solar system.
Scientists say the discoveries provide further evidence that the Earth and its neighbors may not be as special as we like to think, boosting the potential for life elsewhere in the universe.
One of the so-called exoplanets is known to be the second planet orbiting a single star. It was only the second time astronomers have found more than one planet orbiting a star outside our own solar system.
``The findings suggest that it's quite common to have planets around other stars, so our solar system is not as unique as we might think,'' said Jim O'Donnell, a spokesman for the International Astronomical Union. ``That makes the possibility of life in the universe more likely.''
Three teams of researchers from Switzerland and the United States presented evidence of 10 discoveries at an International Astronomical Union conference in the northern English city of Manchester. Two of the discoveries turned out to be the same planet.
Scientists from Switzerland's Geneva Observatory told the meeting about the discovery of six new planets, including one that is the second orbiting a star. The star is known as HD 83443, slightly smaller than our sun and some 141 light years from Earth.
A light year is the distance light will travel in a year in a vacuum, about 6 trillion miles.
Scientists from the University of California at Berkeley said they discovered three exoplanets - including one also discovered by the Swiss group.
Additionally, astronomers based at the University of Texas at Austin's McDonald Observatory discovered a Jupiter-sized planet orbiting the star Epsilon Eridani, 10.5 light years from Earth.
The Berkeley scientists also found evidence suggesting that five stars known to have one orbiting planet may in fact have more - an indication that multi-planet systems such as our own may be common.
``This is the first time anyone has noticed that such a high percentage of stars with one known planet show evidence of a second companion,'' said Dr. Deborah Fischer, a member of the Berkeley team.
Scientists have now found 50 exoplanets, 41 of them in the last five years. Too far away to be seen with even the most high-powered telescopes, they are detected by observing how the gravitational pull of a circling planet can cause a wobble in a star's movement. By measuring the size and frequency of the wobble, scientists can calculate the mass and orbit of the planet.
The planet detected by the McDonald Observatory team orbits a star, Epsilon Eridani, that is near enough to be seen with the naked eye. That makes Epsilon Eridani the closest star to our solar system known to have a planet circling it. Epsilon Eridani is also similar in size to our sun.
McDonald Observatory team leader Dr. William Cochran said the planet was 297 million miles from Epsilon Eridani, leaving open the possibility of more planets closer in. By contrast, Earth is about 93 million miles from the sun.
``It means there could be room for an Earth-like planet closer to Epsilon Eridani and - perhaps - in a habitable zone,'' he said.
It is the possibility of multi-planet solar systems like our own that sets astronomers' pulses racing. But research on the subject has far to go.
Astronomers' instruments can only sense the wobble caused by a big planet, so an Earth-sized planet - more likely to have an atmosphere capable of sustaining life - could not be detected.
Still, the pace of new discoveries is quickening.
``We're now at a stage where we are finding planets faster than we can investigate them and write up the results,'' said Berkeley team leader Dr. Geoffrey Marcy.
``It's wonderful. Planet-hunting has morphed from the marvelous to the mundane.''