[Paper Review] TNOs are Cool! A Survey of the transneptunian Region XV. Physical characteristics of 23 resonant transneptunian and scattered disk objects

Anikó Farkas-Takács, Csaba Kiss+8 more|arXiv (Cornell University)|Feb 28, 2020

Astro and Planetary Science74 references2 citations

TL;DR

This study determines the size, albedo, and thermal properties of 23 resonant trans-Neptunian and scattered disk objects using thermal emission data from Herschel/PACS and Spitzer/MIPS, applying radiometric modeling. It confirms a bimodal albedo-color distribution in the trans-Neptunian region, strengthening evidence for a compositional discontinuity in the early Solar System.

ABSTRACT

The goal of this work is to determine the physical characteristics of resonant, detached and scattered disk objects in the transneptunian region, observed mainly in the framework of the "TNOs are Cool!" Herschel Open Time Key Program. Based on thermal emission measurements with the Herschel/PACS and Spitzer/MIPS instruments we determine size, albedo, and surface thermal properties for 23 objects using radiometric modelling techniques. This is the first analysis in which the physical properties of objects in the outer resonances are determined for a notable sample. In addition to the results for individual objects, we have compared these characteristics with the bulk properties of other populations of the transneptunian region. The newly analyzed objects show a large variety of beaming factors, indicating a diversity of thermal properties, and in general, they follow the albedo-colour clustering identified earlier for Kuiper belt objects and Centaurs, further strengthening the evidence for a compositional discontinuity in the young Solar System.

Motivation & Objective

• To determine the physical characteristics—size, albedo, and surface thermal properties—of 23 resonant trans-Neptunian and scattered disk objects.
• To assess the diversity of thermal properties and albedo-color relationships in the outer Solar System.
• To evaluate whether color or spectral slope can reliably predict albedo for size distribution studies.
• To test the validity of using a single albedo value for converting absolute magnitude to diameter across different dynamical populations.
• To examine whether size correlates with albedo within albedo-color groups, especially in resonant objects.

Proposed method

• Radiometric modeling of thermal emission data from Herschel/PACS and Spitzer/MIPS instruments at 70, 100, and 160 µm.
• Use of multi-wavelength far-infrared photometry to derive effective diameter and geometric albedo.
• Incorporation of visible absolute magnitude and spectral slope data to constrain albedo-color group membership.
• Application of a thermal model to compute beaming factors and infer surface thermal inertia.
• Cluster analysis of albedo and color data to identify distinct compositional groups.
• Comparison of results with previous studies to assess consistency and improve size-albedo conversion methods.

Experimental results

Research questions

• RQ1 Do resonant trans-Neptunian objects exhibit a bimodal albedo-color distribution similar to other trans-Neptunian populations?
• RQ2 Can spectral slope or visible color reliably predict geometric albedo for size estimation in different dynamical classes?
• RQ3 Is there a systematic trend between object size and albedo within albedo-color groups, particularly for resonant objects?
• RQ4 Do objects in different resonances (e.g., 2:1, 3:2, 5:3) show distinct thermal or albedo properties?
• RQ5 Can a single mean albedo be used to convert absolute magnitude to diameter across all trans-Neptunian populations, or is a color-dependent albedo model necessary?

Key findings

• The 23 analyzed objects exhibit a wide range of beaming factors, indicating diverse surface thermal properties.
• Objects in the bright-red (BR) group have a mean geometric albedo of pV(RTNO,BR) = 0.12 ± 0.04, while the dark-neutral (DN) group has pV(SDO,DN) = 0.044 ± 0.008.
• The scattered disk and detached objects show a clear bimodal albedo distribution, with distinct albedos for the BR and DN groups.
• No obvious trend is observed between size and albedo within albedo-color groups, suggesting albedo is not systematically size-dependent in these populations.
• The presence of objects with high spectral slopes (S′ ≲ 0) and low albedos suggests that color alone is not a perfect proxy for albedo in all cases, especially in resonant populations.
• The study supports the use of color- or spectral slope-based albedo proxies in size distribution studies, rather than a single average albedo, to improve accuracy.