OSSOS XX: The Meaning of Kuiper Belt Colors

Abstract

Observations show that 100 km class Kuiper Belt objects (KBOs) can be divided into (at least) two color groups, red (R; g−i<1.2) and very red (VR; g−i>1.2), reflecting a difference in their surface composition. This is thought to imply that KBOs formed over a relatively wide range of radial distance, r. The cold classicals at 42au <r<47 au are predominantly VR, and known Neptune Trojans at r ; 30 au are mostly R. Intriguingly, however, the dynamically hot KBOs show a mix of R and VR colors and no correlation of color with r. Here we perform migration/instability simulations where the Kuiper Belt is populated from an extended planetesimal disk. We find that the color observations can be best understood if R objects formed at r<r * and VR objects at r>r * , with 30au <r * <40 au. The proposed transition at 30au <r * <40 au would explain why the VR objects in the dynamically hot population have smaller orbital inclinations than the R objects, because the orbital excitation from Neptune weakens for orbits starting beyond 30 au. Possible causes of the R-VR color bimodality are discussed.

Col-OSSOS: Probing Ice Line/Color Transitions within the Kuiper Belt’s Progenitor Populations

“…Additionally, the higher inclinations and eccentricities of neutral-colored objects (Marsset et al 2019;Ali-Dib et al 2021) suggest that they formed closer to the planetary region. This inner neutral/outer red disk is similar to the work of Nesvorný et al (2020) and Ali-Dib et al (2021), where alternative dynamical models of the Kuiper Belt throughout Neptune's migration were used to investigate KBO surface colors. In this inner neutral/outer red, if the color transition were far enough out in the disk, it could potentially still support the origin scenario for the blue binaries.…”

“…bar on this disk layout reaches all the way to 30 au, this suggests that transition positions beyond 30 au could be possible in the potential case that the initial disk extended beyond 30 au. Nesvorný et al (2020) also explored possible color transition positions in the primordial Kuiper Belt. They used a model of Kuiper Belt formation with a similar primordial disk between 24 and 30 au but with the addition of a low-mass disk extension from 30 to 40 au.…”

“…Our chosen dynamical model has a truncated initial disk at 30 au, and our analyzed sample of Col-OSSOS colors was unable to rule out this scenario. Recent works have explored dynamical models with a low-mass disk extension beyond 30 au (e.g., Nesvorný et al 2020;Ali-Dib et al 2021). In the case of the inner neutral/outer red disk, the most probable color transition may have been pushed out further than 28 au if we had used a dynamical model with an extended disk.…”

“…The precision of the colors measured by Col-OSSOS, combined with the well-characterized discovery survey (OSSOS; Bannister et al 2018), enables the accurate investigation of the primordial color distributions. Figures 6 and 7 in Nesvorný et al (2020) show a detailed comparison between OSSOS observations and a dynamical model biased by the OSSOS survey simulator. The dynamical model of the planetesimal disk throughout Neptune's migration used in this work (Nesvorný & Vokrouhlický 2016) matches the orbital structure of the Kuiper Belt while maintaining a precise history of each dynamical test particle.…”

Effect of H2S on the Near-infrared Spectrum of Irradiation Residue and Applications to the Kuiper Belt Object (486958) Arrokoth

“…Arrokoth and all CC-KBOs are classified as ultra-red objects: color slope of 28% per 100 nm at 550 nm for Arrokoth (Grundy et al 2020). Connecting the color slope of small icy objects in the solar system to a particular chemical composition could provide a very powerful way to trace back the history of the solar system and explicitly test results suggested by dynamical models (Morbidelli et al 2005;Nesvorný et al 2020). The chemistry and spectroscopy of S-rich residue could be a tracer for specific regions and specific environments of the early solar system (Wakelam et al 2011).…”