The provenance and evolution of comets

Abstract

The process of comet formation through the hierarchical aggregation of originally submicron-sized interstellar grains to form micron-sized particles and then larger bodies in the protoplanetary disc, culminating in the formation of planetesimals in the disc extending from Jupiter to beyond Neptune, is briefly reviewed. The 'planetesimal' theory for the origin of comets implies the existence of distinct cometary reservoirs, with implications for the immediate provenance of observed comets (both long-period and shortperiod) and their evolution as a result of planetary perturbations and physicd decay, for example splitting and sublimation. The principal mode of cometary decay and collisional interaction with the terrestrial planets is through the formation and evolution of streams of cometary debris and hitherto undiscovered 'families' of cometary asteroids. Recent dynamical results, in particular the sungrazing and sun-colliding end-state for short-period comet and asteroid orbits, are briefly discussed.

Resonant meteoroids from Comet Tempel-Tuttle in 1333: the cause of the unexpected Leonid outburst in 1998

“…Indeed, recent work (e.g. Bailey 1996) has emphasized some surprising similarities in the long‐term orbital evolution of these otherwise rather different classes of orbit. As far as the Leonids are concerned, Comet 55P/Tempel‐‐Tuttle is well known to be in the 5/14 mean‐motion resonance with Jupiter (Stoney & Downing 1899).…”

Sun-grazing orbit of the unusual near-Earth object 2004 LG

“…This is because the impacts were recorded over timescales much longer than those allowing deterministic orbit propagation. Thus, with exception of a few very rare cases (e.g., comet P96/Machholz; e.g., Bailey et al 1992;Bailey 1996;Levison & Dones 2007), no definite predictions about the solar impacts were made for specific bodies.…”