Centaurs are icy planetesimals located between Jupiter and Neptune. They cross the orbits of one or more of the giant planets in their journey around the Sun, and interactions with these outer planets cause the orbits of Centaurs to be inherently unstable. For this reason, they are thought to be transitory objects that have been scattered out of the Kuiper Belt (perhaps more specifically the scattered disk) and will soon be ejected from the Solar System, or are in the process of transitioning from Kuiper Belt objects (KBOs) to Jupiter-family comets.

Evidence to support their origin in the Kuiper Belt lies in the observation that they have similar sizes, spectral properties and colour distributions to KBOs. Their end status as a Jupiter-family comet (a short-period comet also thought to originate in the Kuiper Belt), is suggested by observations of the first detected Centaur, Chiron. Originally classified as an asteroid, Chiron has subsequently developed a cometary coma and is now classified as both an asteroid and a comet. This potential for dual classification (as an asteroid and as a comet) prompted the name, Centaur, as in the half-man-half-horse beast from Greek mythology.

There are almost 250 Centaurs and scattered disk objects currently known.