Red-dwarf stars bear little resemblance to our sun. They are about a quarter as heavy and give off a tiny fraction of the energy. If our sun is a powerful light bulb, they are tiny Christmas lights, less than 1 percent as bright. But astronomers at the Harvard-Smithsonian Center for Astrophysics say that solar systems that formed around red dwarfs, which are far more common in our galaxy than stars like the sun, may hold the nearest habitable planets.

At a press conference in Cambridge last Wednesday, scientists said that of the 75 billion red dwarf stars in our galaxy, 6 percent are circled by earth-like planets at a habitable distance that would allow liquid water to exist.