To the list of planets orbiting distant stars, add another 715. That’s the number of planets, strewn among 305 planetary systems, popping out of the observational data from NASA’s Kepler space telescope.
“We’ve almost doubled today the number of planets known to humanity,” said Jack Lissauer, a NASA planetary scientist, announcing the discovery during a teleconference Wednesday with reporters. The findings will be published in March in two scientific papers in the Astrophysical Journal.
These new planets are all in multi-planet systems and are relatively modest in size — most of them smaller than Neptune. Four of the new planets are about twice the size of Earth and are in orbits that put them in what is considered the habitable zone of their stars, at a distance that could allow water to be in a liquid state at the surface.
There are surely more habitable-zone planets out there, scientists said in the teleconference. Small planets in very tight orbits are the ones most likely to be detected by Kepler, which looks for the dimming of starlight as a planet passes, or “transits,” the disk of the star as seen from the telescope. The star, planet and telescope have to be aligned, a matter of pure chance: Planets that are orbiting at a great distance from the parent star are less likely to be lined up propitiously.
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