Origin of volatiles in the Main Belt

TL;DR

This paper explores how icy particles formed in the outer Solar Nebula could have migrated inward to become part of the Main Belt asteroids, influencing their composition, porosity, and density, and proposes methods to infer early Solar System conditions.

Contribution

It introduces a model for the formation and inward migration of icy planetesimals and discusses how their detection can reveal early Solar Nebula conditions and asteroid properties.

Findings

Ices in the outer Solar Nebula are composed of clathrate hydrates, hydrates, and pure condensates.

A significant fraction of icy planetesimals migrated inward without vaporizing.

Presence of ices affects asteroid porosity and bulk density.

Abstract

We propose a scenario for the formation of the Main Belt in which asteroids incorporated icy particles formed in the outer Solar Nebula. We calculate the composition of icy planetesimals formed beyond a heliocentric distance of 5 AU in the nebula by assuming that the abundances of all elements, in particular that of oxygen, are solar. As a result, we show that ices formed in the outer Solar Nebula are composed of a mix of clathrate hydrates, hydrates formed above 50 K and pure condensates produced at lower temperatures. We then consider the inward migration of solids initially produced in the outer Solar Nebula and show that a significant fraction may have drifted to the current position of the Main Belt without encountering temperature and pressure conditions high enough to vaporize the ices they contain. We propose that, through the detection and identification of initially buried ices revealed by recent impacts on the surfaces of asteroids, it could be possible to infer the thermodynamic conditions that were present within the Solar Nebula during the accretion of these bodies, and during the inward migration of icy planetesimals. We also investigate the potential influence that the incorporation of ices in asteroids may have on their porosities and densities. In particular, we show how the presence of ices reduces the value of the bulk density of a given body, and consequently modifies its macro-porosity from that which would be expected from a given taxonomic type.