Only A Trillion: New Earths

Five of the candidates are Earth-sized.

The announcement from the Kepler space telescope team brings the total number of exoplanet candidates they have identified to more than 1,200.

The data release also confirmed a unique sextet of planets around a single star and 170 further solar systems that include more than one planet circling far-flung stars.

The Kepler telescope was conceived to hunt for exoplanets, staring into a small, fixed patch of the sky in the direction of the constellations Cygnus and Lyra.

It looks for the minuscule dimming of light that occurs when an exoplanet passes in front of its host star. Kepler spots "candidate" planets, which typically are confirmed by ground-based observations to confirm their existence.

In just its first few months of operation, as a paper posted to the Arxiv server reports, Kepler has spotted 68 Earth-sized candidates, 288 so-called "super-Earths" that are up to twice Earth's size, 662 that are Neptune-sized, and 184 that are even larger.

On Wednesday, members of the team announced it had confirmed the Kepler-11 solar system, comprising six large exoplanets tightly circling an eight billion-year-old star that lies about 2,000 light-years away.

"The fact that we've found so many planet candidates in such a tiny fraction of the sky suggests there are countless planets orbiting sun-like stars in our galaxy," said William Borucki, who heads Kepler's science programme at Nasa's Ames Research Center.

"We went from zero to 68 Earth-sized planet candidates and zero to 54 candidates in the habitable zone, some of which could have moons with liquid water."

The bountiful nature of the data from just a few months of observing time from Kepler makes profound suggestions about the preponderance of exoplanets in general, and about the existence of multiple planets around single stars in particular.

In a separate paper, team members outlined how the Kepler candidates include 115 stars that host a pair of planets, 45 with three, eight stars with four, one with five planets, and Kepler-11, which hosts six.
"Even in first four months of Kepler data, a rich population of multiples appeared, and we recognised this was going to be a very important discovery," David Latham, of the Harvard-Smithsonian Center for Astrophysics, told BBC News.