[Previous] | [Session 24] | [Next]
D.J. Scheeres (Univ. of Michigan), S.J. Ostro (JPL/Caltech), E.I. Asphaug (UC-Santa Cruz), R.S. Hudson (Wash. State Univ.)
Rubble-pile asteroids can have their shapes and spin states altered, perhaps dramatically, by close planetary encounters (Bottke et al. 1998, Planet. Space. Sci. 46,311; 1999, Astron. J. 117,1921). However, despite their popularity, the relative abundances of rubble-pile and monolithic asteroids as a function of size are unknown. At least one tiny asteroid, 1998 KY26, certainly is monolithic (Ostro et al. 1999, Science 285, 557), and the harsh angularity of 6489 Golevka ( Hudson and Ostro 1995, BAAS 27, 1062) and prominent linear ridges on 4179 Toutatis (Hudson and Ostro 1995, Science 270, 84) may suggest monolithic interiors.
We present an initial exploration of the effects of close planetary encounters on the spin states of monolithic asteroids using both analytical and numerical techniques. Our analysis can be applied to an arbitrary flyby geometry between a planet and an asteroid of any shape and initial spin state. We have used the theory to guide numerical integrations of Toutatis' interaction with the Earth during a close flyby. Our results indicate that such flybys may have placed an initially uniformly rotating Toutatis into its current rotational state. Application of the analysis over a wider parameter space may indicate the degree to which close encounters share responsibility for current near-earth asteroid spins.
This research was funded by NASA's Planetary Geology and Geophysics program.