We Now Know 1000 Worlds That Could Support Life

NASA's planet hunting Kepler Space Telescope is on a roll! The telescope has monitored more than 150,000 stars beyond our solar system since its launch, and has highlighted more than 4,000 candidate exoplanets for further analysis. As of Tuesday, NASA announced the verification of the 1000th of those worlds, adding to the "Kepler Hall of Fame."

That stunning milestone was reached after eight more candidates spotted by the plant-hunting telescope were verified - that is, experts found that they are indeed planets.

That may sound a little silly, having to make sure that what a state-of-the-art $600 million (including launch cost) telescope says is real actually is. Kepler was, after all, designed to identify exoplanets that not only are real, but fit a "Goldilocks" description, being "just right" to support life.

However, as any expert will be quick to tell you, identifying planets hundreds-of-thousands of light-years away is no simple task, and there's plenty of room for error.

For instance, this past summer, experts from Penn State's Center for Exoplanets and Habitable Worlds found that a pair of very promising goldilocks exoplanets may not even actually exist. Instead, they were likely just "Doppler illusions," a confusing set of noises in spectroscopic observations.

How can this be? Many exoplanets are way too far away for even Kepler to actually see. Instead, astronomers measure how a star dims and wobbles when its orbiting planets pass in front of it. Those cues tell us the size, density, and distance of these planets - important clues as to whether they are terrestrial worlds that could boast life. However, data of this nature should always be observed with a healthy amount of skepticism, at least until it is verified like Kepler-438b and Kepler-442b, two of NASA's newly validated planets. (Scroll to read on...)

"Kepler collected data for four years - long enough that we can now tease out the Earth-size candidates in one Earth-year orbits," Fergal Mullally, the SETI Institute Kepler scientist who led the analysis of a new candidate catalog, said in a statement. "We're closer than we've ever been to finding Earth twins around other Sun-like stars. These are the planets we're looking for."

Both new exoplanets orbit stars smaller and cooler than our Sun, making their habitable zone closer to their parent star, in the direction of the constellation Lyra. These results were recently accepted for publication and are due to appear in The Astrophysical Journal and its supplementary journal.

"With each new discovery of these small, possibly rocky worlds, our confidence strengthens in the determination of the true frequency of planets like Earth," added study co-author Doug Caldwell. "The day is on the horizon when we'll know how common temperate, rocky planets like Earth are."

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