Col-OSSOS: Investigating the Origins of Different Surfaces in the Primordial Kuiper Belt

Abstract

The Colours of the Outer Solar System Origins Survey (Col-OSSOS) measured the optical/NIR colours of a brightness-complete sample of Trans-Neptunian Objects (TNOs). Like previous surveys, this one found a bimodal colour distribution in TNOs, categorised as red and very red. Additionally, this survey proposed an alternative surface classification scheme: FaintIR and BrightIR. Cold classical TNOs mostly have very red or FaintIR surfaces, while dynamically excited TNOs show a mixture of surfaces. This likely indicates that formation locations and proximity to the Sun influenced surface characteristics and color changes. Our study combines the data from Col-OSSOS with two dynamical models describing the formation of the Kuiper belt during Neptune's migration. We investigate the proposed surface-colour changing line and explore the distribution of different surfaces within the primordial disk. By comparing radial colour transitions across various scenarios, we explore the origins of surface characteristics and their implications within the context of BrightIR and FaintIR classifications. Moreover, we extend our analysis to examine the distribution of these surface classes within the present-day Kuiper Belt, providing insights into the configuration of the early solar system's planetesimal disk prior to giant planet migration. We find that the most likely primordial disk compositions are inner neutral / outer red (with transition $30.0^{+1.1}_{-1.2}$ au), or inner BrightIR / outer FaintIR (with transition $31.5^{+1.1}_{-1.2}$ au).