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TheCybele asteroids (also known as the "Cybeles") are adynamical group ofasteroids, named after the asteroid65 Cybele.^[1] Considered by some as the last outpost of an extendedasteroid belt, the group consists of just over 2000 members and a few collisionalfamilies.^[2][3] The Cybeles are in a 7:4orbital resonance withJupiter. Their orbit is defined by an osculatingsemi-major axis of 3.27 to 3.70AU,^[2] with aneccentricity of less than 0.3,^[1] and aninclination less than 30°.^[2]

The dynamical Cybele group is located adjacent to the outermostasteroid belt, beyond theHecuba gap – the 2:1 resonant zone with Jupiter, where theGriqua asteroids are located – and inside the orbital region of theHilda asteroids (3:2 resonance), which are themselves followed by theJupiter trojans (1:1 resonance) further out.

Three knownasteroid families exist within the Cybele group: theSylvia family (603), theHuberta family and theUlla family (903). A potential fourth family is a small cluster with the parent body(45657) 2000 EK.^[2] A fifth family, named after522 Helga, was identified in 2015.^[3]

The Cybele asteroids87 Sylvia and107 Camilla aretriple systems with more than onesatellite. Other large members include121 Hermione,76 Freia,790 Pretoria, and566 Stereoskopia.^[1]

The group is thought to have formed from the breakup of a larger object in the distant past.^[1] While most members areC- andX-type asteroids, NASA'sWide-field Infrared Survey Explorer also measuredalbedos of some Cybele asteroids that are typical for stonyS-type asteroids.^[2]

Total of 2034 Cybeles with osculating semi-major axis between 3.28 and 3.7 AU. Low numbered members of the collisionalSylvia (SYL) and smallerUlla (ULA) families are also marked.