[Paper Review] Colors and taxonomy of Centaurs and Trans-Neptunian Objects

D. Perna, M. A. Barucci+7 more|Dec 14, 2009

Astro and Planetary Science4 citations

TL;DR

This study presents visible and near-infrared photometric observations of 31 Centaurs and Trans-Neptunian Objects (TNOs), classifying 28 using the Barucci et al. (2005a) taxonomy system via G-mode analysis. It reveals a bimodal color distribution in Centaurs (BR and RR types), confirms IR-classified objects are predominantly classical TNOs, and finds no strong dominance of RR types among classical TNOs in this sample, suggesting diverse surface evolution histories across dynamical classes.

ABSTRACT

The study of the surface properties of Centaurs and Trans-Neptunian Objects (TNOs) provides essential information about the early conditions and evolution of the outer Solar System. Due to the faintness of most of these distant and icy bodies, photometry currently constitutes the best technique to survey a statistically significant number of them. Our aim is to investigate color properties of a large sample of minor bodies of the outer Solar System, and set their taxonomic classification. We carried out visible and near-infrared photometry of Centaurs and TNOs, making use, respectively, of the FORS2 and ISAAC instruments at the Very Large Telescope (European Southern Observatory). Using G-mode analysis, we derived taxonomic classifications according to the Barucci et al. (2005a) system. We report photometric observations of 31 objects, 10 of them have their colors reported for the first time ever. 28 Centaurs and TNOs have been assigned to a taxon. We combined the entire sample of 38 objects taxonomically classified in the framework of our programme (28 objects from this work; 10 objects from DeMeo et al. 2009a) with previously classified TNOs and Centaurs, looking for correlations between taxonomy and dynamics. We compared our photometric results to literature data, finding hints of heterogeneity for the surfaces of 4 objects.

Motivation & Objective

• To investigate the surface properties of Centaurs and TNOs through photometric observations, as these bodies preserve primordial material from the outer Solar System's formation.
• To classify a large sample of TNOs and Centaurs using the Barucci et al. (2005a) taxonomy system based on color indices.
• To explore correlations between taxonomic classification and dynamical properties (e.g., semimajor axis, inclination) to infer surface evolution and origin.
• To identify potential surface heterogeneity through multi-epoch or multi-color analysis in selected objects.
• To expand the statistical sample of taxonomically classified TNOs and Centaurs by combining new data with prior literature.

Proposed method

• Visible and near-infrared photometry was conducted using FORS2 and ISAAC instruments on the Very Large Telescope (VLT) at ESO, Chile.
• Color indices (B-V, V-R, V-I, V-J, V-H, V-K) were measured to characterize surface reflectance properties.
• The G-mode statistical method was applied to assign each object to a taxonomic class (BB, BR, IR, RR) based on the Barucci et al. (2005a) system.
• The classification was validated by comparing with literature data and assessing consistency across multiple observations.
• Dynamical properties (semimajor axis, orbital inclination, distance) were extracted from orbital elements to correlate with taxonomy.
• Average colors for each taxonomic class were computed from the full sample of 151 classified objects, including new and literature data.

Experimental results

Research questions

• RQ1 Do the color properties of Centaurs and TNOs correlate with their dynamical classes, such as classical, resonant, or scattered populations?
• RQ2 Is there a detectable distribution bias of taxonomic classes (BB, BR, IR, RR) across different dynamical populations?
• RQ3 Are there signs of surface heterogeneity in individual objects, suggesting complex surface evolution or composition?
• RQ4 How do the average color indices of each taxonomic class compare across the full sample of 151 classified TNOs and Centaurs?
• RQ5 Does the distribution of taxonomic types vary with semimajor axis or orbital inclination, indicating dynamical sorting or evolutionary processes?

Key findings

• Ten of the 31 observed objects had their colors reported for the first time, significantly expanding the photometric database for TNOs and Centaurs.
• Twenty-eight of the 31 observed objects were successfully classified using the Barucci et al. (2005a) taxonomy system via G-mode analysis.
• The study confirms the well-known color bimodality in Centaurs, with 13 objects classified as BR and 10 as RR, indicating distinct surface populations.
• All four newly classified IR-type objects are classical TNOs, supporting the trend that IR types are concentrated in resonant and classical dynamical classes.
• Among classical TNOs in this sample, the four taxonomic classes are more evenly distributed than previously suggested, challenging the dominance of RR types in this population.
• RR-type objects are predominantly found at low inclinations, consistent with the 'cold' population, while BB-types are enriched at high inclinations, aligning with the 'hot' population.