Energetic collisions in the asteroid belt produce several observable effects, altering their size distribution and rotational properties. Moreover, interesting objects or systems may be created: dynamical families, or binaries, and asteroids in unusual rotation states (fast rotators or tumbling bodies). While the evolution of the size distribution and properties of families as well as binaries are discussed in separate chapters, the other relevant effects of collisions will be dealt with here. During collisions, both the projectile and the target bring their own spin and orbital angular momenta to the system. In the collision the fragments may acquire a "breakup spin" connected to the breakup process. The "breakup spin" is related to the ejection velocity and size of the fragment; fast and small ejecta can achieve rapid spin rates. Usually, freshly created fragments leaving a collisional site do not spin around their axis of maximum momentum of inertia; thus, tumbling (observed also in laboratory experiments) is "natural." The presence of dissipative processes damps the wobbling, with a timescale that is usually short compared to the age of the solar system. Observations of main-belt asteroids suggest a lower limit of ~2 h to their spin periods. Very fast rotators, which must be monolithic bodies held together by internal strength, are present only among the smallest observed asteroids (all of which are NEAs, owing to obvious selection effects). Several asteroids have very long rotational periods, which remains puzzling. Theoretical arguments give preliminary and qualitative explanations for the observed properties. Asteroidal binary systems are an expected outcome from catastrophic collisions, through the effect of the mutual gravitational interaction or as a consequence of later bursting fission.
Side effects of collisions: Spin Rate Changes, Tumbling Rotation States, and Binary Asteroids
PAOLICCHI, PAOLO;
2002-01-01
Abstract
Energetic collisions in the asteroid belt produce several observable effects, altering their size distribution and rotational properties. Moreover, interesting objects or systems may be created: dynamical families, or binaries, and asteroids in unusual rotation states (fast rotators or tumbling bodies). While the evolution of the size distribution and properties of families as well as binaries are discussed in separate chapters, the other relevant effects of collisions will be dealt with here. During collisions, both the projectile and the target bring their own spin and orbital angular momenta to the system. In the collision the fragments may acquire a "breakup spin" connected to the breakup process. The "breakup spin" is related to the ejection velocity and size of the fragment; fast and small ejecta can achieve rapid spin rates. Usually, freshly created fragments leaving a collisional site do not spin around their axis of maximum momentum of inertia; thus, tumbling (observed also in laboratory experiments) is "natural." The presence of dissipative processes damps the wobbling, with a timescale that is usually short compared to the age of the solar system. Observations of main-belt asteroids suggest a lower limit of ~2 h to their spin periods. Very fast rotators, which must be monolithic bodies held together by internal strength, are present only among the smallest observed asteroids (all of which are NEAs, owing to obvious selection effects). Several asteroids have very long rotational periods, which remains puzzling. Theoretical arguments give preliminary and qualitative explanations for the observed properties. Asteroidal binary systems are an expected outcome from catastrophic collisions, through the effect of the mutual gravitational interaction or as a consequence of later bursting fission.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
