65489 Ceto is a
binary trans-Neptunian object (TNO) discovered on March 22, 2003 by
C. A. Trujillo and
M. Brown at
Palomar. It is named after the sea goddess
Ceto from Greek mythology. The object was identified as a
binary on April 11, 2006 by K. Noll, H. Levison, W. Grundy and D. Stephens using the Hubble Space Telescope; the companion object is named
Phorcys (, formally
(65849) Ceto I Phorcys), after
the Greek sea god. Using an extended definition of a
centaur as an object on a non-resonant (unstable) orbit with its perihelion inside the orbit of Neptune, the Ceto system can be considered the second known binary centaur. It came to
perihelion in 1989.