Forming the Cold Classical Kuiper Belt in a light Disk

TL;DR

This paper proposes a new model for forming the Cold Classical Kuiper Belt from a much less massive disk, emphasizing the role of small grains and high formation efficiency, which aligns with observed properties.

Contribution

The model demonstrates that a light, cold belt of small grains can efficiently produce large Kuiper Belt Objects, challenging the need for a massive primordial disk.

Findings

High formation efficiency of large bodies from a light belt.

Mass spectrum peaks at an intermediate size, matching observations.

The observed size distribution break may be primordial, not due to erosion.

Abstract

Large Kuiper Belt Objects are conventionally thought to have formed out of a massive planetesimal belt that is a few thousand times its current mass. Such a picture, however, is incompatible with multiple lines of evidence. Here, we present a new model for the conglomeration of Cold Classical Kuiper belt objects, out of a solid belt only a few times its current mass, or a few percent of the solid density in a Minimum Mass Solar Nebula. This is made possible by depositing most of the primordial mass in grains of size centimetre or smaller. These grains collide frequently and maintain a dynamically cold belt out of which large bodies grow efficiently: an order-unity fraction of the solid mass can be converted into large bodies, in contrast to the ~0.1% efficiency in conventional models. Such a light belt may represent the true outer edge of the Solar system, and it may have effectively halted the outward migration of Neptune. In addition to the high efficiency, our model can also produce a mass spectrum that peaks at an intermediate size, similar to the observed Cold Classicals, if one includes the effect of cratering collisions. In particular, the observed power-law break observed at ~30 km for Cold Classicals, one that has been interpreted as a result of collisional erosion, may be primordial in origin.