Tau Ceti
On December 19, 2012, evidence was presented that suggested a system of five planets orbiting Tau Ceti. The planets' estimated minimal masses were between 2 and 6 Earth masses, with orbital periods ranging from 14 to 640 days. One of them, Tau Ceti e, appears to orbit about half as far from Tau Ceti as Earth does from the Sun. With Tau Ceti's luminosity of 52% that of the Sun and a distance from the star of 0.552 AU, the planet would receive 1.71 times as much stellar radiation as Earth does, slightly less than Venus with 1.91 times Earth's. Nevertheless, some research places it within the star's habitable zone. The Planetary Habitability Laboratory has estimated that Tau Ceti f, which receives 28.5% as much starlight as Earth, would be within the star's habitable zone, albeit narrowly.