Astronomers have discovered three Earth-sized planets orbiting a small red sun, just 40 light-years away. Researchers say all three worlds are potentially habitable and could represent the best targets yet in the search for life beyond the solar system.

"These are not massive, hot, super exotic worlds," said Julien de Wit, a postdoctoral associate in planetary science at MIT who worked on the study describing the find. "All three of them are close to one Earth (radius), and each of them could be suitable for life."

The system's host star, called TRAPPIST-1, is what is known as an ultracool dwarf. It is about one-tenth the size of our sun and just a bit bigger than Jupiter.

Its two innermost planets orbit extremely close to the star, taking just 1.5 and 2.4 Earth days respectively to complete a turn around the ultracool dwarf. The third planet's orbital period is less certain: Current observations suggest its orbital period could range anywhere from 4 to 73 days.