Polarimetry of trans-Neptunian objects (136472) Makemake and (90482) Orcus^⋆

¹ LESIA-Observatoire de Paris, CNRS, UPMC Univ. Paris 06, Univ. Paris-Diderot, 5 place J. Janssen, 92195 Meudon Pricipal Cedex, France
e-mail: irina.belskaya@obspm.fr; sonia.fornasier@obspm.fr; antonella.barucci@obspm.fr
² Institute of Astronomy, Kharkiv National University, 35 Sumska str., 61022 Kharkiv, Ukraine
³ Armagh Observatory, College Hill, Armagh BT61 9DG, Northern Ireland, UK
e-mail: sba@arm.ac.uk; ast@arm.ac.uk
⁴ INAF – Oss. Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
e-mail: tozzi@arcetri.astro.it
⁵ Department of Physics, University of Helsinki, PO Box 64, Gustaf Hällströmin katu 2a, 00014, Finland
e-mail: karri.muinonen@helsinki.fi
⁶ Finnish Geodetic Institute, PO Box 15, Geodeetinrinne 2, 02431 Masala, Finland

Received: 10 August 2012
Accepted: 25 September 2012

Abstract

Context. We study the surface properties of trans-Neptunian 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 carried out linear polarisation measurements of Makemake and Orcus.

Results. Polarisation of Orcus is similar to that of smaller-sized objects. The polarimetric properties of Makemake are very close to those of Eris and Pluto. We did not find any significant differences in the polarisation properties of trans-Neptunian objects (TNOs) from different dynamical classes. However, there are significant differences in the polarisation of the large objects and the smaller ones and between large TNOs with water-ice and methane-ice dominated surfaces.

Conclusions. We confirm the different types of polarisation phase behaviour for the largest and smaller-sized 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.