Cybele asteroids

The Cybele asteroids (also known as the "Cybeles") are a dynamical group of asteroids, named after the asteroid 65 Cybele.^[1] 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.^[2][3] The Cybeles are in a 7:4 orbital resonance with Jupiter. Their orbit is defined by an osculating semi-major axis of 3.27 to 3.70 AU,^[2] with an eccentricity of less than 0.3,^[1] and an inclination less than 30°.^[2]

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.^[2] A fifth family, named after 522 Helga, was identified in 2015.^[3]

The Cybele asteroids 87 Sylvia and 107 Camilla are triple systems with more than one satellite. Other large members include 121 Hermione, 76 Freia, 790 Pretoria, and 566 Stereoskopia.^[1]

The group is thought to have formed from the breakup of a larger object in the distant past.^[1] 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.^[2]

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