Fig. 6: Collision velocities of two equal-mass satellites as a function of the satellite’s mass and the orbital distance of the impact point.
From: Multiple moonlet mergers as the origin of the Dinkinesh-Selam system
The lobes that formed Selam are massive relative to the primary, meaning that their orbital velocity is small compared to their mutual escape velocity. In this regime, the collision velocity is weakly dependent on the orbital distance, and most collisions occur at about vesc owing to the mutual gravitational attraction of the two lobes, which increases their relative speed leading up to the collision. The mass of each satellite needed for the formation of Dimorphos is m = 5 × 10−3 × Mprimary.
