Water ice in the Kuiper belt

TL;DR

This study analyzes near-infrared spectra of Kuiper belt objects and centaurs to understand water ice distribution, revealing three distinct surface types linked to formation history and compositional differences.

Contribution

It provides a comprehensive classification of water ice presence on KBOs and centaurs, connecting spectral features to formation and evolutionary processes.

Findings

Water ice occurs in three distinct manners on KBOs and centaurs.

Haumea family members show nearly pure water ice surfaces.

Large objects with H<3 have water ice possibly from cryovolcanism.

Abstract

We examine a large collection of low resolution near-infrared spectra of Kuiper belt objects and centaurs in an attempt to understand the presence of water ice in the Kuiper belt. We find that water ice on the surface of these objects occurs in three separate manners: (1) Haumea family members uniquely show surfaces of nearly pure water ice, presumably a consequence of the fragmentation of the icy mantle of a larger differentiated proto-Haumea; (2) large objects with absolute magnitudes of $H<3$ (and a limited number to H=4.5) have surface coverings of water ice - perhaps mixed with ammonia - that appears to be related to possibly ancient cryovolcanism on these large objects; and (3) smaller KBOs and centaurs which are neither Haumea family members nor cold-classical KBOs appear to divide into two families (which we refer to as "neutral" and "red"), each of which is a mixture of a common nearly-neutral component and either a slightly red or very red component that also includes water ice. A model suggesting that the difference between neutral and red objects is due to formation in an early compact solar system either inside or outside, respectively, of the ~20 AU methanol evaporation line is supported by the observation that methanol is only detected on the reddest objects, which are those which would be expected to have the most of the methanol containing mixture.