First results from the RENOIR survey: A Possible Evidence of Surface Transformation of Centaurs

Centaurs are small bodies residing on unstable orbits between Jupiter and Neptune. As objects recently scattered from their sources in the Kuiper belt and beyond, they carry the compositional information of their parent populations into the realm of the giant planets. Unlike the TNO populations, Centaurs are known for their unusual bimodal distribution of optical surface colors, splitting them into two distinct groups - red and grey (neutral). It has been long disputed whether this color distribution points to Centaurs being sourced from two distinct formation locations in the protoplanetary disk, or alternatively that the present surface color distribution represents an ongoing dynamical-evolutionary pathway experienced by Centaurs that produces the two groups.

Here we present results from a broadband visible photometric investigation using the SDSS-like g', r' and i' filters of 33 Centaurs obtained with the Gemini Observatories and the Lowell Discovery Telescope. The data have been collected as a part of the RENOIR (Revealing cENtaur cOlor hIstoRy) survey in 2022-2025. The ultimate goal of this program is to collect surface colors of Centaurs covering a wide range of diameters and occupying the entire heliocentric distance span of the Centaur region. 

Our preliminary results suggest that the (g'-r') color distribution of our target Centaurs is different from that of TNOs measured by the Col-OSSOS program (Buchanan et al. 2022) with a 2-sigma confidence level, and while our targets' colors do display bimodality in (g'-r') - space, they are also significantly shifted towards the neutral part of the color-color plot. This shift potentially points out to a surface color transformation the pristine TNOs undergo during their dynamical evolution in the Centaur region. We have also coupled our observational results with the analysis of each Centaur’s orbital history in order to explore possible correlations of orbital evolution with present-day observed surface colors.