Astronomy rivals 'close' in search for a new Earth

FOUR planets have been discovered by astronomers in the space of a week, leading scientists to predict that the finding of solar systems similar to ours could be drawing closer.

Planet hunting is the hottest field in astronomy, with hundreds of researchers joining a race that a decade ago was reserved for a few dreamers. This past week has been a dizzying one, with three teams in the United States and Europe rushing to announce discoveries of previously unknown exoplanets - those orbiting stars other than our sun.

Some appear smaller and more solid - more like Earth and Mars - than the gaseous giants identified before, although none of these new bodies would be mistaken as Earth’s twin.

Yesterday, NASA released details of what the space agency describes as a "new class" of exoplanets found by one of the American teams, led by University of California-Berkeley astronomer Geoffrey Marcy.

At least two of the bodies are probably comparable in scale to intermediate-sized planets in our solar system like Neptune and Uranus, which are about 14 times the mass of Earth. Many previous exoplanets have been closer to the size of Jupiter - 318 times the mass of Earth.

David Charbonneau, of the Harvard Smithsonian Centre for Astrophysics in Cambridge, Massachusetts, where scientists announced a competing discovery last week, said: "It’s been a great week. They have finally broken through to a new level."

Now many experts say it will not be long before astronomers detect planets that are similar to Earth’s dimensions and characteristics - perhaps even suitable for sustaining life, with an oxygen-rich atmosphere and oceans.

Alan Boss, a planet formation theorist at the Carnegie Institution in Washington, said: "We are getting closer to finding a solar system more like our own - with an Earth-sized planet."

What makes the American discovery noteworthy is it was found through a network of small telescopes.

In the next 20 years, NASA hopes to launch new space observatories to get a sharper view of exoplanets. The first, the Kepler observatory, is scheduled to launch in 2007.

Meanwhile, astronomers caution against jumping to grand conclusions. Timothy Brown, of the National Centre for Atmospheric Research in Boulder, Colorado, who was a leader of the Harvard Smith-sonian team, said: "Very few solar systems seem to be built along the same lines as ours."

He also compared planet-hunting today to early biologists being confounded by strange new specimens.

He said: "You think all fish have fins, and then you pull up an octopus. There’s just a vast amount that we don’t know."