So experts were quite surprised when they determined (from years of observing asteroid light curves) the spins and orientations of 10 members of the Koronis family of minor planets.
Koronis family members that are rotating prograde (turning in the same direction as they orbit) have axes aligned with each other to point toward Cassiopeia.
Ida belongs to the Koronis family of asteroids, apparently created when a collision shattered a larger parent body into 100 or more pieces.
Alternatively, the moon may represent a true daughter of Ida - a chip off the old asteroid knocked free long after the creation of the Koronis family. In this scenario, a projectile rammed into Ida, gouging out a small chunk of material that became locked in orbit around the asteroid, much the way scientists believe our moon formed from Earth.
The Karin cluster is part of the much larger
Koronis family. However, in this and other older family associations, the orbits have been changed too much by subsequent collisions, gravitational disturbances, and radiation pressure to be traced back to a common origin.
Since Ida is a member of the
Koronis family, Dactyl's existence may be a direct result of the collision on the family's parent body.
from the Sun), the Eos family (326, 3.0 a.u.), and the
Koronis family (400, 3.1 a.u.).
Ida itself belongs to the Koronis family, a collection of roughly 150 minor planets with similar orbits that are likely the remains of a larger precursor shattered while colliding with another object.
Binzel has found that members of the Koronis family exhibit subtle color differences not unlike those seen on Ida and Dactyl.
Most probably the two objects ended in the same vicinity after the collision long ago that created the
Koronis family of asteroids, to which Ida belongs.