Tau Ceti is a star. Much like our sun, Tau Ceti hosts planets. Of the five planets that revolve around Tau Ceti, one—called HD 10700e—is about half the distance from Tau Ceti as the Earth is from the sun. But, HD 10700e is smaller than Earth and Tau Ceti isn't as strong as our sun, so the planet falls into the "habitable zone," where liquid water can exist. And it's only 12 light-years from Earth. Additionally, someone claims to have found three planets in the habitable zone of a three-star system that's 22 light-years away.