Belgian astronomers have been observing an ultracool red dwarf star called TRAPPIST-1 that is only slightly larger than the gas giant and just 40 light years away. Orbiting it, they have discovered three earth-sized exoplanets. The two closest to their star probably receive too much radiation to be hospitable to life, but the third might be far enough away to be in a habitable zone. About 15 percent of stars relatively close to our Solar System are red dwarfs. Astronomers reason that they provide an opportunity to find smaller, Earth-like cousins that would be invisible against the background light of larger stars.