An Investigation on the Origin of Centaurs’ Color–Inclination Relation

Abstract

Since its discovery, there has been a debate in the past few decades on the origin of the bimodal color distribution of Centaurs. Two theories have been proposed to explain this bimodal color distribution: (1) evolutionary processes resulting in changes of the surface properties of Centaurs, and (2) compositional differences inherited from the source region of Centaurs. Interestingly, Centaurs also show a correlation between their orbital inclinations and colors such that blue and red Centaurs tend to be characterized by high and low inclination distributions, respectively. In this study, these two hypotheses are investigated, and it is found that hypothesis (2) is more likely to be the origin of the color–inclination relation of Centaurs assuming that the scattered Kuiper Belt objects (SKBOs) also have a color–inclination relation, and this relation is statistically preserved when they evolved into Centaurs. This hypothesis is further justified by performing numerical simulations on 158 observed Centaurs and 82 observed SKBOs. Finally, it is suggested that the “outside-in” external photoevaporation happening during the early stage of the solar system might be related to the puzzling color–inclination relation observed in Centaurs and, possibly, other trans-Neptunian object subgroups.