A NASA telescope taking a nose count of planets in one small neighbourhood of the Milky Way has found more than 1200 candidates, including 54 residing in life-friendly orbits around their parent stars.
Scientists have no way of knowing yet if any of the newly discovered planets are solid-body worlds like Earth. But the census, collected by NASA's Kepler Space Telescope after just four months of work, shows that small planets like Earth are much more prevalent than Jupiter-sized worlds. It also revealed multiple-planet systems are common.
"We think we're seeing about 200 multi-planet systems," says astronomer Daniel Fabrycky of University of California, Santa Cruz. "That really blew us away. We didn't expect that this would be one of Kepler's discoveries."
The findings increase the number of planet candidates identified so far by Kepler to 1235. Of these, 68 are approximately Earth-size; 288 are two to three times the size of Earth; 662 are Neptune-size; 165 are the size of Jupiter and 19 are larger than Jupiter.
Of particular note: a brood of six - the largest extrasolar planet family found so far - circling a Sun-like star named Kepler 11. Five are puffy planets formation-flying closer than Mercury orbits the Sun.
Astronomers suspect Kepler 11, located about 2000 light years from Earth, has more offspring farther away or beyond Kepler's viewing angle.
Detecting planets around faraway stars
The telescope sees a planet's footprints as it passes across the face of its parent star, just like a gnat flying past your computer screen will block a bit of light.
When a planet orbits behind the star, relative to Kepler's view, there is a slight increase in brightness. From the frequency and duration of the dimming and brightening scientists can figure out how far away a planet orbits and how much mass it contains.
Kepler, which monitors stars in the constellation Cygnus, was launched to find out how many Earth-like worlds are orbiting a sampling of 156,000 stars like the sun.
Finding an Earth-sized world circling as far from its star as Earth orbits the Sun will take 365 days of observations to detect one pass, plus another year or two of data to verify the orbital period.
If Kepler's latest head count is confirmed, the list of extrasolar planets will more than triple.
"One of the things that is still a work in progress is to figure out how many of the candidate planets are real planets," says Assistant Professor Jonathan Fortney, also of astronomy and astrophysics.
"This is some kind of planetary tsunami," says astronomer Geoff Marcy, with the University of California, Berkeley. "The implication is that there are lots and lots of Earth-sized planets in our Milky Way."
An independent analysis by astrophysicists at the California Institute of Technology (Caltech) shows Kepler's track record of finding extrasolar planets is better than 80 per cent.
The Kepler 11 study appears in this week's Nature, while the Caltech analysis appears on the pre-press website arXiv.org.
The Kepler science mission data, collected between 2 May and 16 September 2009, released by NASA, will be published in an upcoming issue of The Astrophysical Journal.