The world's largest and most prolific team of planet hunters has announced the discovery of 28 new planets outside our solar system, raising to 236 the total number of known exoplanets.

Among the 28 new worlds are at least four new multiple-planet systems, says astronomer Professor Chris Tinney, of the UNSW School of Physics, who heads the Australian part of the team.

The planets were found by closely observing their gravitational pull on their parent stars: "The more we look, the more we find planets," said Professor Tinney, whose team used the Anglo-Australian Observatory, near Coonabarabran.

"Something like 10 to 15 per cent of stars host gas giants. A larger fraction of stars may host planets too small for us to detect."

Professor Tinney says the growing pace of discovery makes it increasingly likely that our own Milky Way galaxy is swarming with much smaller, rocky and potentially habitable worlds too small to detect with existing technology.

The discoveries come from the combined work of the California and Carnegie Planet Search team and the Anglo-Australian Planet Search team and were reported at the semi-annual meeting of the American Astronomical Society in Honolulu by University of California, Berkeley, post-doctoral fellow Jason T. Wright and PhD John Asher Johnson.

The full story is available on the Faculty of Science website.