Are the Fragments of Comet Shoemaker-Levy 9 Swarms of Meter-Sized Planetesimals?

Previous abstract Next abstract

Session 4 -- Solar System
Display presentation, Monday, 30, 1994, 9:20-6:30

[4.04] Are the Fragments of Comet Shoemaker-Levy 9 Swarms of Meter-Sized Planetesimals?

T.W.Rettig (Univ Notre Dame), M.J.Mumma (NASA/Goddard), S.C.Tegler, J.Hahn (Univ Notre Dame)

The tidally fragmented comet S-L 9 presently exhibits 21 major concentrations of material (sub-nuclei) as well as extended dust wings. Comet S-L 9 is the first inactive comet observed to fragment under the influence of tidal forces alone. In contrast to the analysis of Weaver et al. (1994) where each subnucleus is interpreted to contain a compact body 3-4 km in diameter, we investigate the possibility that each subnucleus is composed of tidally fragmented `swarms' of $\sim$ 50-m sized planetesimals. Our swarm model for the subnuclei suggests the upcoming impact of comet S-L 9 with Jupiter will result in vaporization of these bolides high in the Jovian stratosphere.

Recent models of planetesimal accumulation in the solar nebula favor development of a bi-modal size distribution before the onset of gravitational instability triggers formation of larger bodies (Weidenschilling 1993). The dominant modal sizes at Uranus-Neptune are $\sim$ 50-m and $<$ 10-cm. The former agrees well with the size estimates of outbursting volumes in cometary nuclei (Whitney 1955, Rettig et al. 1992, Mumma et al. 1993). We thus might expect 50-m sized cometesimals and cm-sized particles to have accreted into km-sized bodies, several of which then combined to form a larger cometary nucleus.

It is likely that tidal disruption of S-L 9 occurred episodically, with the weaker bound units disrupting first. The fragment cloud would have stretched out in a tube along the tidal direction. After perijove, we show the decreasing tidal force permits self-gravity to re-focus material forming ($\sim$20) fragments. We also demonstrate that after apjove there will be a critical distance where tidal dispersal begins again. This critical distance can be used to determine the individual swarm masses. Our tidally disrupted swarm model explains the dust wings, the 21 subnuclei, and predicts only slight modification to the Jovian atmosphere during the July 1994 impact.

Monday program listing