The count – the most extensive ever carried out – would seem to boost the chances that there is alien life elsewhere in the universe.
Astronomers from the University of California used the giant W M Keck Observatory in Hawaii to check out 166 sun-like stars in our own part of the galaxy.
In a five-year survey, they checked for orbiting planets between three and 1,000 the mass, or size, of the Earth.
Their results, reported this week in the journal Science, found more small planets than large ones, indicating that small worlds are more common in our Milky Way.
Leader of the investigation Andrew Howard said it was like counting boulders, rocks and pebbles in a canyon. He said: “We found more rocks than boulders, and more pebbles than rocks.
“Our ground-based technology can’t see the grains of sand, the Earth-size planets, but we can estimate their numbers. Earth-size planets in our galaxy are like grains of sand sprinkled on a beach – they are everywhere.”
The team’s research mean that potentially habitable planets also be common. NASA’s Kepler spacecraft also is currently searching sun-like stars for planets and is expected to find the first true rocky worlds like Earth in the next few years.
In February 2008, results from the NASA’s Spitzer space telescope suggested that 60 per cent of stars in the Sun’s vicinity are likely to have rocky planets orbiting them.
• Discover space for yourself and do fun science with a telescope. Here is Skymania’s advice on how to choose a telescope. We also have a guide to the different types of telescope available. Check out our monthly sky guide too!
