Scientists using telescopes by the European Southern Observatory did not find any planets quite the size of Earth or any that seemed habitable or even unusual. But their announcement that 32 new planets had been found increased the number of planets discovered outside the solar system to more than 400.

Six of the newly found planets are several times bigger than Earth, increasing the number of known "SuperEarths" by more than 30%. Most planets discovered so far are far bigger, with many Jupiter-sized or even larger.

Two of the newly discovered planets were just five times the size of Earth, while one was up to five times larger than Jupiter.

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Astronomer Stephane Udry of the University of Geneva said the results support the theory that planet-formation is common, especially with certain type of common stars.

"I'm pretty confident that there are Earth-like planets everywhere," Dr Udry said. "Nature doesn't like a vacuum. If there is space to put a planet there, there will be a planet there."

What astronomers said is especially exciting is the high percentage - about half - of a type of star systems with relatively light stars that had planets around them. This is more than planet-formation theory expected, astronomers said. Two of the four planets found around these type stars were relatively close to Earth size.

The discoveries were made by the High Accuracy Radial Velocity Planet Searcher, which looks for slight wobbles in a star's movements, which would be made by the tug of a planet's gravity on the star. There are no photos of these planets.