Spin vector evolution for inner solar system asteroids

The spin vector evolution of 30 asteroids in the inner solar system is investigated using 10 different orbital integrations for each object, since the orbital evolutions are chaotic for all the objects examined. Close encounters with major planets and resonances involving Jupiter, the Earth or Venus are common. Frequency-related zones, chaotic or non-chaotic, can be found for all the spin integrations for most of the objects. The positions and properties of these zones are in most cases rather independent of which of the 10 orbital integrations is used. The asteroids can be classed according to orbital behaviour, and it is found that the frequency-related zones for objects belonging to certain classes have common properties. The frequency analysis shows that the power spectra of most objects are dominated by frequencies in the range [−60,−20]″/yr. A statistical analysis showed no tendencies to a drift to a more prograde or retrograde distribution of spin vectors. There were, however, clear tendencies for some spin vector directions to be more probable than others during the time period examined. In particular highly retrograde spins seem to be more probable than slightly retrograde ones.