Asteroids on Earth-like orbits and their origin

The orbit of 1991 VG and a set of other asteroids whose orbits are very similar to that of the Earth have been examined. Its origin has been speculated to be a returning spacecraft, lunar ejecta or a low-inclination Amor- or Apollo-class object. The latter is arguably the more likely source, which has been investigated here. The impact probability for these objects has been calculated, and while it is larger than that of a typical near-Earth asteroid (NEA), it is still less than 1:200 000 over the next 5000 yr. In addition, the probability of an NEA ever ending up on an Earth-like orbit has been obtained from numerical simulations and turned out to be about 1:20 000, making this a rare class of objects. The typical time spent in this state is about 10 000 yr, much less than the typical NEA lifetime of 10 Myr.