MOFFETT FIELD, Calif. — In just its first four months of operation, the Kepler orbiting observatory has identified 1,235 candidate planets, including five in orbit in a habitable zone around a slightly smaller, cooler star than our Sun.

“Kepler has blown the lid off of everything we’ve known about Earth-sized planets,” says Yale University astronomer Debra Fischer. While she expects that as many as 20% of the candidate planet sightings will prove false after confirming studies by ground observatories, Kepler’s listings boost the count of exoplanets — planets outside our Solar System — by more than twice the 520 discovered by ground observatories in the 16 years before the spacecraft’s launch in March 2009. Kepler has also found 170 stars with multiple planet systems, says Principal Scientist William Borucki of NASA’s Ames Research Center here.

The Kepler findings are drawn from observations of 156,000 stars in a portion of the Cygnus and Lyra galaxies and cover just 1/400th of the sky. They were made in just a 4-month period from May-September 2009. The satellite orbits the Sun and trails the Earth.

In the journal Nature, 38 scientists on the Kepler team say they have found 54 new planet candidates within the habitable zones of their host star, five of which are near Earth-sized. The rest range in size from a “super-Earth” — twice as big as our planet — to larger than Jupiter.

In all, Kepler, has found 68 Earth-sized planets, 288 that are super-Earth-sized, 662 the size of Neptune, 165 about equal to Jupiter and 19 larger than that.

While the “Holy Grail” of the Kepler mission is to find apparently habitable Earth-sized planets, it will not be able to confirm that life exists on even the most “perfect” matches. Habitable zones are similar to the 1 million mi. that Earth orbits the Sun, neither so close as to be too hot for life or so far as to be too cold. A habitable temperature range is regarded as zero to 200F, Borucki says.

Two stars have been confirmed as having multiple planets — Kepler 9 with three and Kepler 11 with six. The latter, shown in an artist’s rendering, is drawing the most attention because it has so many and they lie in an even flatter plane than our own Solar System. Five of the planets exist in a habitable zone.

All of its planets are larger than Earth, with two comparable to Uranus and Neptune. The inner-most planet, Kepler-b, is 10 times closer to its star than Earth is to the Sun. The outermost, Kepler-g, is half as far from its star as the Earth is from the Sun.

The Kepler-11 star is 2,000 light years from Earth, meaning the light Kepler observed from it originated about the time Anthony was stabbing Julius Caesar.