Effects of gravitational interactions on asteroid spin states

We demonstrate that mutual gravitational interactions between an asteroid a nd a planet or another asteroid can play an important role in shaping an as teroid's spin state. We focus on two situations that asteroids may encounte r during their lifetimes. The first is the environment after creation from a disrupted parent asteroid, when there may be many asteroid fragments inte racting gravitationally with each other before their mutual escape. The oth er is the interaction between an asteroid and a planet during a hyperbolic flyby. In each case the mutual gravitational interaction can alter the aste roid's spin state. We derive analytical descriptions of the effects and per form numerical simulations to explore the interactions and to give examples , The net effect of many small interactions, taken in isolation, is to caus e the asteroid to spin at a faster rate-although this must be balanced agai nst all other effects that influence spin rates. Conversely, the effect of a single, strong interaction can fundamentally change an asteroid's spin st ate, causing it to tumble and significantly increasing or decreasing its ov erall angular momentum. We simulate interactions of a sphere of arbitrary m ass with Toutatis and find that these types of gravitational interactions c an provide partial explanations for the current Toutatis rotational state. (C) 2000 Academic Press.