New insights on ices in Centaur and Transneptunian populations

Abstract

A Large Program (LP) has been carried out at ESO-VLT using almost simultaneously the UT1, UT2 and UT4 telescopes (Cerro Paranal, Chile). The aim of this Large Program was to obtain simultaneous visible and near-IR spectroscopic measurements (using FORS, ISAAC and SINFONI instruments) with a S/N ratio as high as possible for almost all objects among different dynamical groups observable within the VLT capability.In this paper we present results on the second half of the Large Program which includes new near-infrared spectroscopy data of 20 objects. For 12 of them for which we had obtained the complete spectral range (V+J+H+K bands), we apply a radiative transfer model to the entire spectral range to constrain their surface composition.We also present an analysis of all near-IR spectral data available on TNOs and Centaurs from both the complete LP and the literature. An overview for a total sample of 75 objects is thus carried out analyzing the ice content with respect to the physical and dynamical characteristics.The major new results are: i) all objects classified as BB class seem to have icy surfaces; ii) the possible presence of CH 3 OH has primarily been detected on very red surfaces (RR class objects) and iii) the majority of Centaurs observed multiple times have an heterogeneous composition.

Methanol ice on the surface of minor bodies in the solar system

“…Other interesting objects that may provide new insights into the history of the solar system could be those that are covered by highly volatile species, such as methanol. Methanol is more volatile than H 2 O and CO 2 and has been reported on the surface of several objects such as Pholus (see Cruikshank et al 1998), 2002 ), and possibly 2004TY 364 , 2004UX 10 , 2008FC 76 , and 2008 (see Barucci et al 2011). Methanol is expected to be mainly destroyed by space weathering (Hudson & Moore 1999) or could be lost by sublimation within 15−20 AU (Brown et al 2011).…”

“…Pholus has been observed several times during the last two decades in the visible (VIS) and in the nIR range with the 2.4 m Hiltner telescope, the UKIRT and the VLT facilities (see Cruikshank et al 1998;Barucci et al 2011). A complete VISnIR spectrum has been performed in the first half of the '90s by Cruikshank et al (1998).…”

“…Investigating their surface by spectroscopy is a tool for constraining the chemical properties and the evolution processes that occurr in the solar system. Unfortunately, most of the spectra of TNOs (Guilbert et al 2009;Merlin et al 2010a;or Barucci et al 2011, for recent publications) are almost featureless in the visible as well as in the nearinfrared (nIR) range and it is difficult to extract valuable information concerning the initial composition of these objects, the nature of the irradiated products and the role of each radiation source. This problem is important for objects that suffered much irradiation, therefore we need to focus our efforts on objects covered with relatively fresh ices.…”

“…Recent observations performed with 8-m-class telescopes allowed us to obtain new chemical information from nIR spectroscopy (Barucci et al 2011). Most of these objects seem to be covered by water ice (see Barkume et al 2008, for instance).…”

“…We first present new spectral analyses of the Centaur Pholus and a comparison with previous results from Cruikshank et al (1998) to constrain the spectral features observed in the nIR range and investigate the spectral variations. Then, we will use these results with those obtained by Barucci et al (2006Barucci et al ( , 2011 on the surface of the TNOs (55638) 2002 VE 95 and2004 TY 364 , on which the presence of methanol and water ice is possible, to compare the chemical and physical properties of the surface of these three dynamically different objects. Finally, we present new laboratory measurements that have been performed to constrain the spectral behavior of CH 3 OH-H 2 O mixtures depending on the ratio of each component and the ambient temperature.…”