Tau Ceti e and Tau Ceti f are exoplanets orbiting, fairly obviously, the star Tau Ceti, a G-type main sequence star in the constellation Cetus (usually referred to as “the whale”, but actually a sea monster from Greek mythology). They are the fourth and fifth planets out from the star, and were discovered on December 19th, 2012, by the “radial velocity” method, the oldest known means of detecting planets outside our system.
Both planets are likely to be a fair bit bigger than the Earth (“f” could be up to seven times larger), and they had initially excited astronomers by possibly being in the habitable zone of Tau Ceti. It was thought they could have temperatures of up to 50 or 60°C, which is plenty warm enough for the existence of life. Unfortunately though, later refinements have suggested this might not be the case, and also unfortunately for any potential Tau Cetians, the parent star is known to have an extensive “debris disk”, meaning that any planets nearby would face a regular pounding by rocks of varying shapes and sizes, almost certainly including some big enough to cause serious problems for any fledgling species trying to evolve.