We investigate the origins of the photometrically very red (VR) and less red (LR) trans-Neptunian objects (TNOs).
We first reanalyze the Col-OSSOS based data set of Marsset et al. 2019 and find that in addition to the known color–inclination correlation in hot TNOs, a similar trend exists for color–eccentricity.
We show that VR TNOs are sharply constrained to eccentricities <0.42 and inclinations <21°, leading to a paucity of VR scattered disk and distant mean motion resonance objects.
We then interpret these findings using N-body simulations accounting for Neptune’s outward migration into a massless particles disk and find that these observations are best reproduced with an LR-to-VR color transition line between ∼38 and 42 au in the primordial disk, separating the objects’ formation locations.
A color transition around 38 au is needed to explain the high abundance of VR plutinos, but it creates too many VR scattered disk objects, while a transition line around 42 au seems to better reproduce the scattered disk colors but creates virtually no VR plutinos.
Our simulations furthermore show that the rarity of VR particles at high eccentricity is possibly due to the absence of sweeping higher-order MMRs and secular resonances, beyond 42 au.