Scientists have discovered three Earth-sized planets that look ideally suited to search for signs of life beyond our solar system. A team of astronomers from MIT and the University of Liege detected three planets orbiting an ultracool dwarf star -- just 40 light years from Earth using a prototype telescope called TRAPPIST which is capable of looking at 60 nearby ultracool stars. NPR reports: The closest planet to the star orbits in about one and a half Earth days. From the planet's surface, the star would look like a reddish ball fixed to one spot in the sky. Scientists don't yet know the mass of the planets or what they're made of. Astronomers have discovered more than a thousand planets outside our solar system, but it's still rare to find ones that look promising in terms of habitability."These planets are Earth-sized, they are temperate -- we can't rule out the fact that they are habitable -- and they are well-suited for atmospheric studies," says Julien de Wit, a researcher at MIT.