In order to clarify the role of comets as Earth impactors and bringers of organics to the young planet, we present a study of the influence of tidal splitting in this context. Evidence from Comet Shoemaker-Levy 9 indicates low values for the density and material strength. Such values have been used to model the evolution of a comet in an orbit leading to Earth impact. We find that cometary nuclei impacting the Earth with radii gta 0.1 - 0.3km will split just before doing so. Nuclei of several km radius will split when passing within a distance lta 5-8 Earth radii. Cometary nuclei with radii gta 1km stand a much larger chance of being tidally split than of hitting the Earth. Consequently, streams of fragments and debris form in Earth-crossing orbits more often than large nuclei cause impacts. The mass distribution of impacting material is shifted toward sub-km objects that are apt to air bursting, whereby the survivability of organics may be significantly increased. If the cometary impactors move in orbits where the expected number of passages within Earth's Roche zone is gta 5, we estimate that most of the material reaching Earth's surface and originating in km-sized nuclei will appear in the form of split fragments.
IAU Joint Discussion
- Pub Date: