Composition of KBO (50000) Quaoar

Abstract

<i>Aims. <i/>The objective of this work is to investigate the physical properties of objects beyond Neptune – the new frontiers of the Solar System – and in particular to study the surface composition of (50 000) Quaoar, a classical Transneptunian (or Kuiper Belt) object. Because of its distance from the Sun, Quaoar is expected to have preserved, to a degree, its original composition. Our goals are to determine to what degree this is true and to shed light on the chemical evolution of this icy body.<i>Methods. <i/>We present new near-infrared (3.6 and 4.5 <i>μ<i/>m) photometric data obtained with the <i>Spitzer Space Telescope<i/>. These data complement high resolution, low signal-to-noise spectroscopic and photometric data obtained in the visible and near-infrared (0.4–2.3 <i>μ<i/>m) at VLT-ESO and provide an excellent set of constraints in the model calculation process. We perform spectral modeling of the entire wavelength range – from 0.3 to 4.5 <i>μ<i/>m by means of a code based on the Shkuratov radiative transfer formulation of the slab model. We also attempt to determine the temperature of H<sub>2<sub/>O ice making use of the crystalline feature at 1.65 <i>μ<i/>m. <i>Results. <i/>We present a model confirming previous results regarding the presence of crystalline H<sub>2<sub/>O and CH<sub>4<sub/> ice, as well as C<sub>2<sub/>H<sub>6<sub/> and organic materials, on the surface of this distant icy body. We attempt a measurement of the temperature and find that stronger constraints on the composition are needed to obtain a precise determination.<i>Conclusions. <i/>Model fits indicate that N<sub>2<sub/> may be a significant component, along with a component that is bright at m, which we suggest at this time could be amorphous H<sub>2<sub/>O ice in tiny grains or thin grain coatings. Irradiated crystalline H<sub>2<sub/>O could be the source of small-grained amorphous H<sub>2<sub/>O ice. The albedo and composition of Quaoar, in particular the presence of N<sub>2<sub/>, if confirmed, make this TNO quite similar to Triton and Pluto.