On December 19, 2012, evidence was presented for a system of five planets orbiting Tau Ceti. The planets' estimated minimum masses are between two and six times the Earth's mass. Their orbital periods range 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. This is slightly less than Venus, which gets 1.91 times Earth's. Some research places it within the star's habitable zone. 