The Influence of Mean Motion Resonances on the Outer Kuiper Belt: Does the Outer Kuiper Belt have a Future?

Abstract

It often seems as though papers bearing titles in the form of a question end with ambiguous answers. Here the situation is different: the outer Kuiper belt does have a definite future, although one of uncertain duration. Simulations provide two distinct, compelling reasons. First, mean motion resonances in the outer belt [i.e., beyond the 1/2 resonance at 47.76 AU] are amazingly "sticky": in almost all cases bodies captured in them from regions closer to Neptune during that planet's outward migration remain trapped for 4.6 byr. Most captured orbits are chaotic and so will eventually escape, but there is no reason to believe that all outer belt resonances will empty in the near future. Second, in determining capture probabilities for various resonances, we find that the first order 1/2 resonance is quite efficient, but, in clear contrast to higher order ones in the outer belt, nearly half of its victims have escaped during 4.6 byr. These bodies typically remain in unstable orbits in the outer belt, usually for several hundred million years before being expelled well beyond 100 AU. Other inner belt resonances, although capturing less efficiently than 1/2, behave in the same fashion. Thus the outer belt has a two component, long-term population: one with members lying semi-permanently in one of about 6 resonances and another that is far more temporary, but whose source provides a continuous and ready resupply. The resulting eccentricity distribution of this combined population closely matches the observed one, as Hahn and Malhotra have made clear but the inclination distribution is a better approximation to it than is often claimed, a fact that probably should not be ignored when considering an origin for what has been labeled "the scattered disk".