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 nearly 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.