The paths of the sun's planets take up billions of kilometers of space, but now astronomers using NASA's Kepler spacecraft (shown) have spotted an alien solar system with five planets whose orbits could all fit inside a region that's just a quarter the size of Mercury's path. Kepler found the planets going around the star KOI 500 by detecting the tiny dips they cause when they pass in front of their sun, dimming its light ever so slightly. The planets are somewhat larger than Earth, and all five make Mercury, the sun's fastest planet, which whirls around our star every 88 days, seem like a laggard. Their years are just 1.0, 3.1, 4.6, 7.1, and 9.5 days long, so they're the perfect place to reside if you like frequent birthday parties—and can stand the heat.
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