Asteroid 2012 XE133: A transient companion to venus

Abstract

Apart from Mercury that has no known co-orbital companions, Venus remains as the inner planet that hosts the smallest number of known co-orbitals (two): (322756) 2001 CK32 and 2002 VE68. Both objects have absolute magnitudes 18 < H < 21 and were identified as Venus co-orbitals in 2004. Here, we analyse the orbit of the recently discovered asteroid 2012 XE133 with H = 23.5 mag to conclude that it is a new Venus co-orbital currently following a transitional trajectory between Venus' Lagrangian points L5 and L3. The object could have been a 1:1 librator for several thousand years and it may leave the resonance with Venus within the next few hundred years, after a close encounter with the Earth. Our calculations show that its dynamical status as co-orbital, as well as that of the two previously known Venus co-orbitals, is controlled by the Earth-Moon system with Mercury playing a secondary role. The three temporary co-orbitals exhibit resonant (or near-resonant) behaviour with Mercury, Venus and the Earth and they follow rather chaotic but similar trajectories with e-folding times of the order of 100 yr. Out of the three co-orbitals, 2012 XE133 currently follows the most perturbed path. An actual collision with the Earth during the next 10 000 yr cannot be discarded; an encounter at 0.005 au may take place in 2028, but even closer encounters are possible within that time frame. Extrapolation of the number distribution of Venus co-orbitals as a function of the absolute magnitude suggests that dozens of objects similar to 2012 XE133 could be transient companions to Venus. Some additional objects that were or will be transient co-orbitals to Venus are also briefly discussed. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.