461 more Kepler exoplanets found, analysis expects 17 billion Earth-sized planets

Kepler mission scientists announced Monday that a new batch of analysis yielded 461 more exoplanet candidates - and that is from within a relatively small cross-section of our galaxy, bringing the total number of potential planets awaiting confirmation to 2,740. Of the several dozen Earth-sized planets, the smallest of 5 categories, 4 were found to be located within their stars' habitable zone, which is defined as an orbit where surface water can exist as a liquid.

Candidates require additional follow-up observations and analyses to be confirmed as planets. At the beginning of 2012, 33 candidates in the Kepler data had been confirmed as planets. Today, there are 105.

Very solid results for the just 4 year old planet-searching Kepler telescope, which identifies planet candidates by repeatedly measuring the change in brightness of more than 150,000 stars in search of planets that pass in front, or "transit," their host star. At least three transits are required to verify a signal as a potential planet.

Since the last official announcement of Kepler candidates in Feb. 2012 the number of smaller Earth- and super-Earth-sized worlds observed has risen considerably, as well as the identification of multi-planet systems that are organized more-or-less along a flat plane... just like ours.

"The large number of multi-candidate systems being found by Kepler implies that a substantial fraction of exoplanets reside in flat multi-planet systems," said Jack Lissauer, planetary scientist at NASA's Ames Research Center in Moffett Field, Calif. "This is consistent with what we know about our own planetary neighborhood."

At the same day of the new Kepler exoplanet candidate announcement, a separate analysis of the Kepler catalogue which extrapolates the data based on probabilities, extending it to all 100 billion stars in our Milky Way galaxy, was presented. The study calculates that about 17 percent of stars have an Earth-sized planet in an orbit closer than Mercury, which would equal the stunning number of at least 17 billion Earth-sized worlds in our galaxy alone.

Francois Fressin, of the Harvard-Smithsonian Center for Astrophysics (CfA), presented the analysis today in a press conference at a meeting of the American Astronomical Society in Long Beach, Calif. A paper detailing the research has been accepted for publication in The Astrophysical Journal.

The researchers also asked whether certain sizes of planets are more or less common around certain types of stars. They found that for every planet size except gas giants, the type of star doesn't matter. Neptunes are found just as frequently around red dwarfs as they are around sun-like stars. The same is true for smaller worlds. This contradicts previous findings.

"Earths and super-Earths aren't picky. We're finding them in all kinds of neighborhoods," says co-author Guillermo Torres of the CfA.