Ryugu formed as part of an asteroid family, belonging either to Eulalia or Polana. Those asteroid families are likely fragments of past asteroid collisions. The large number of boulders on the surface supports a catastrophic disruption of the parent body. The parent body of Ryugu likely experienced dehydration due to internal heating and must have formed in an environment without a strong magnetic field. After this catastrophic disruption part of the surface was reshaped again by the high speed rotation of the asteroid, forming the equatorial ridge (Ryujin Dorsum). Only the western bulge remained as an older structure.