Surface composition and dynamical evolution of two retrograde objects in the outer solar system: 2008 YB₃ and 2005 VD^⋆

¹ Instituto de Astrofísica de Andalucía – CSIC, Apt 3004, 18080 Granada, Spain
e-mail: npinilla@seti.org
² Instituto de Astrofísica de Canarias – c/vía Láctea s/n, 38200, La Laguna, Tenerife, Spain
³ European Southern Observatory, Alonso de Córdova 3107, Vitacura, 19001 Casilla, Santiago 19, Chile
⁴ IAFE (CONICET-UBA), Ciudad Universitaria, Intendente Guiraldes S/N. Buenos Aires. Argentina
⁵ Fundación Galileo Galilei – INAF, Rambla José Ana Fernández Pérez, 7, 38712 Breña Baja, TF, Spain
⁶ Departamento de Astrofísica, Universidad de La Laguna, 38205, La Laguna, Tenerife, Spain
⁷ Observatório Nacional, COAA, Rua Gal. José Cristino 77, 20921-400 Rio de Janeiro, Brazil
⁸ Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago de Chile, Chile

Received: 16 July 2012
Accepted: 28 November 2012

Abstract

Most of the objects in the trans-Neptunian belt (TNb) and related populations move in prograde orbits with low eccentricity and inclination. However, the list of icy minor bodies moving in orbits with an inclination above 40° has increased in recent years. The origin of these bodies, and in particular of those objects in retrograde orbits, is not well determined, and different scenarios are considered, depending on their inclination and perihelion. In this paper, we present new observational and dynamical data of two objects in retrograde orbits, 2008 YB₃ and 2005 VD. We find that the surface of these extreme objects is depleted of ices and does not contain the “ultra-red” matter typical of some Centaurs. Despite small differences, these objects share common colors and spectral characteristics with the Trojans, comet nuclei, and the group of grey Centaurs. All of these populations are supposed to be covered by a mantle of dust responsible for their reddish-to-neutral color. To investigate if the surface properties and dynamical evolution of these bodies are related, we integrate their orbits for 10⁸ years to the past. We find a remarkable difference in their dynamical evolutions: 2005 VD’s evolution is dominated by a Kozai resonance with planet Jupiter while that of 2008 YB₃ is dominated by close encounters with planets Jupiter and Saturn. Our models suggest that the immediate site of provenance of 2005 VD is the in the Oort Cloud, whereas for 2008 YB₃ it is in the trans-Neptunian region. Additionally, the study of their residence time shows that 2005 VD has spent a larger lapse of time moving in orbits in the region of the giant planets than 2008 YB₃. Together with the small differences in color between these two objects, with 2005 VD being more neutral than 2008 YB₃, this fact suggests that the surface of 2005 VD has suffered a higher degree of processing, which is probably related to cometary activity episodes.