by JOHN MATSON
NASA’s planet-hunting satellite is making the case that it’s a small-world galaxy, after all
Score one for the little guys. After years of obscurity in the corners of distant planetary systems smaller exoplanets are finally shuffling into the spotlight.
NASA’s Kepler spacecraft, built to seek out planets in orbit around faraway stars, has since 2009 been monitoring a vast field of stars to see what kind of planets might be found there. Earlier this year scientists working on the mission announced that they had confirmed 15 exoplanets in Kepler’s field of view and identified an astounding 1,200 or so additional planetary candidates, which are probable planets that await independent validation. Prior to that announcement, only about 500 extrasolar worlds had been discovered since planet searches first began to bear fruit in the 1990s.
One of the most fascinating aspects of the Kepler discovery was the small sizes of the planetary candidates. For years the list of known extrasolar planets had been dominated by massive worlds comparable to or larger than Jupiter, the biggest planet in our solar system. Such massive worlds are the easiest to find, whereas more diminutive planets, of roughly Earth or Neptune size, are much more difficult to spot. But Kepler was designed to be sensitive to those smaller worlds, even the temperate, rocky worlds that might be habitable—and it has not disappointed. The spacecraft is showing that smaller planets are common—more common, in fact, than their larger brethren. At least that is how things look in the inner regions of planetary systems, where Kepler’s data is currently the strongest.
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