Col-OSSOS: Evidence for a Compositional Gradient Inherited from the Protoplanetary Disk?

Abstract

In the present-day Kuiper Belt, the number of compositional classes and the orbital distributions of these classes hold important cosmogonic implications for the solar system. The Colours of the Outer Solar System Origins Survey (Col-OSSOS) recently showed that the observed color distribution of small (H ⪆ 6) trans-Neptunian objects (TNOs) can be accounted for by the existence of only two composition classes, named BrightIR and FaintIR, where the range of colors in each class can be modeled as mixtures of two material end-members. Here, we combine the high-precision photometric measurements of Col-OSSOS with those of previous surveys to investigate the orbital distribution of the two color classes and reinterpret the known color–inclination correlation of TNOs in the context of the BrightIR/FaintIR taxonomy. In addition to confirming the previously reported distinct orbital distributions of these classes, we identify a trend of increasing orbital inclinations toward the bluer end of the optical and near-infrared color distribution of BrightIR objects. Using the output of numerical simulations investigating the orbital evolution of TNOs during their scattering phase with Neptune, we show that this trend could reflect a composition gradient in the early protoplanetary disk, in the range of heliocentric distances over which TNOs from the BrightIR class accreted. However, tensions between this interpretation and the existence of blue contaminants among cold classical TNOs, and possible alternative origins for the detected correlation, currently bear uncertainty on our proposed interpretation.

Surface Composition of Centaurs: insights into the thermal evolution of TNOs

“…They propose that the three groups provide a picture of the ice retention lines in the Solar System that likely occurred in the outer protoplanetary disk, just before a major planetary migration. Recent results strengthen NPA23 hypothesis (Nesvorný et al 2020;Pirani et al 2021;Marsset et al 2023).…”

Col-OSSOS: The Distribution of Surface Classes in Neptune's Resonances

“…As in Figure1, the semimajor axis is scaled by three different amounts, as indicated in the x-axis and separated by gaps, and the symbol shapes are preserved, but the colors of the points indicate BrightIR classification (black) and FaintIR classification (red). The low-inclination and low-eccentricity 4:3 resonator at 36.4 au is particularly evident, as is the classification-inclination dependence, particularly at large-a, noted byMarsset et al (2019) andMarsset et al (2023). Neptune is indicated by the large blue circle.…”

“…The distribution of red and very red TNO surfaces has been reported to have a correlation between inclination (for a recent analysis, see Marsset et al 2019) and eccentricity (Ali-Dib et al 2021) to surface color, which is inferred to be related to differences of formation location and the effects of planetary migration on the populations. The correlation between inclination and surface classification holds when the FaintIR/BrightIR classification system is used (Marsset et al 2023). Marsset et al (2019) also identified a dependence between the final inclinations of TNOs and their formation distances.…”