The Cybele asteroids (also known as the "Cybeles") are a dynamical group of asteroids, named after the asteroid 65 Cybele. Considered by some as the last outpost of an extended asteroid belt, the group consists of just over 2000 members and a few collisional families. The Cybeles are in a 7:4 orbital resonance with Jupiter. Their orbit is defined by an osculating semi-major axis of 3.28 to 3.70 AU, with an eccentricity of less than 0.3, and an inclination less than 25°.
The dynamical Cybele group is located adjacent to the outermost asteroid belt, beyond the Hecuba gap – the 2:1 resonant zone with Jupiter, where the Griqua asteroids are located – and inside the orbital region of the Hilda asteroids (3:2 resonance), which are themselves followed by the Jupiter trojans (1:1 resonance) further out.
Three known asteroid families exist within the Cybele group: the Sylvia family (603), the Huberta family and the Ulla family (903). A potential fourth family is a small cluster with the parent body (45657) 2000 EK. A fifth family, named after 522 Helga, was identified in 2015.
The group is thought to have formed from the breakup of a larger object in the distant past. While most members are C- and X-type asteroids, NASA's Wide-field Infrared Survey Explorer also measured albedos of some Cybele asteroids that are typical for stony S-type asteroids.