5145 Pholus

5145 Pholus ( /ˈfoʊləs/ FOH-ləs; from Greek: Φόλος) is a centaur in an eccentric orbit, with a perihelion less than Saturn's and aphelion greater than Neptune's. Pholus has not come within one astronomical unit of a planet since 764 BC, and will not until 5290. It is believed that Pholus originated as a Kuiper belt object.

It was discovered by David L. Rabinowitz, then of the University of Arizona's Spacewatch Project, and named after Pholus, the brother of the mythological Chiron, after which 2060 Chiron was named, in order to follow the tradition of naming this class of outer planet-crossing objects after centaurs.

Pholus was the second centaur to be discovered and was quickly found to be quite red in color, for which it has been occasionally nicknamed "Big Red". The color has been speculated to be due to organic compounds on its surface.

The surface composition of Pholus has been estimated from its reflectance spectrum using two spatially segregated components: dark amorphous carbon and an intimate mixture of water ice, methanol ice, olivine grains, and complex organic compounds (tholins). The carbon black component was used to match the low albedo of the object.

Unlike the first centaur, 2060 Chiron, Pholus has shown no signs of cometary activity.

The diameter of Pholus is estimated to be 185±16 km .