The stars likely to have the most habitable planets may also have the hardest time importing water to these worlds, planetary scientist Gijs Mulders reported August 5. Faint, red orbs known as M dwarfs make up about 80 percent of the Milky Way's stars. But these dwarf stars tend not to build the giant planets like Jupiter that can fling icy asteroids at dry worlds (M dwarf planetary system illustrated above), as is thought to have happened to Earth. Computer simulations, however, show that lots of small boulders working together within a planet nursery can assume Jupiter's and Saturn's role by relocating ice that helps build livable locales.
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