Polarimetry of transneptunian objects (136472) Makemake and (90482) Orcus

TL;DR

This study uses polarimetric measurements to analyze the surface properties of transneptunian objects Makemake and Orcus, revealing size and surface composition influences on their polarization behavior.

Contribution

It provides new polarimetric data for Makemake and Orcus, highlighting differences related to size and surface ice composition among TNOs.

Findings

Orcus's polarization similar to smaller TNOs

Makemake's polarization akin to Pluto and Eris

Size and surface composition influence polarization behavior

Abstract

Context. We study the surface properties of transneptunian populations of Solar-system bodies. Aims. We investigate the surface characteristics of the dwarf planet (136472) Makemake and the resonant object (90482) Orcus. Methods. Using the FORS2 instrument of the ESO-VLT we have carried out linear polarisation measurements of Makemake and Orcus. Results. Polarisation of Orcus is similar to that of smaller size objects. The polarimetric properties of Makemake are very close to those of Eris and Pluto. We have not found any significant differences in the polarisation properties of objects from different dynamical classes. However, there are significant differences in polarisation of large and smaller size objects, and between large TNOs with water-ice and methane-ice dominated surfaces. Conclusions. We confirm the different types of polarisation phase behavior for the largest and smaller size TNOs. To explain subtle surface polarisation of Pluto, Makemake and Eris we assume that their surfaces are covered by a thin layer of hoarfrost masking the surface structure.