METEORITES FROM THE ASTEROID 6 HEBE

We have numerically integrated the orbits of 18 fictitious fragments ejected from the asteroid 6 Hebe, an S-type object about 200 km across which is located very close to the g = g(6) (or v(6)) secular resonance at a semimajor axis of 2.425 AU and a (proper) inclination of 15 degrees 0. A realistic ejection velocity distribution, with most fragments escaping at relative speeds of a few hundreds m/s, has been assumed. In four cases we have found that the resonance pumps up the orbital eccentricity of the fragments to values > 0.6, which result into Earth-crossing, within a time span of approximate to 1 M yr; subsequent close encounters with the Earth cause strongly chaotic orbital evolution. The closest Earth and Mars encounters recorded in our integration occur at miss distances of a few thousandths of AU, implying collision lifetimes < 10(9) yr. Some other fragments affected by the secular resonance become Mars-crossers but not Earth-crossers over the integration time span. Two bodies are injected into the 3 : 1 mean motion resonance with Jupiter, and also display macroscopically chaotic behaviour leading to Earth-crossing. 6 Hebe is the first asteroid for which a realistic collisional/dynamical evolution route to generate meteorites has been fully demonstrated. It may be the parent body of one of the ordinary chondrite classes.