On the orbital similarity of Earth-crossing asteroids (2101) Adonis and 1995 CS

The orbits of the well-known ∼ 1 km Earth-crossing asteroid (2101) Adonis and the recently-discovered ∼ 50 m asteroid 1995 CS are strikingly similar, their semi-major axes, eccentricities and inclinations differing by little whilst their directions of perihelion are aligned to within about 5°. This indicates that a common origin might be suspected for them. Although 1995 CS was observed over only a three-day arc, its proximity to the Earth at the time means that its orbit is fairly-well determined, and seven possible solutions for that orbit, showing only small deviations, are tabulated. Backwards purely-gravitational integrations of these orbits, along with that of (2101) Adonis, indicate that at least 30,000 yr are required to make any convergence between the orbits of the two bodies possible. If (2101) Adonis is an extinct or dormant comet, which is suspected on other grounds, then it could not have been substantially active during that period else the two would have diverged through the effects of erratic non-gravitational accelerations, which would have been more severe for 1995 CS if it contained any appreciable volatile component. The two objects are therefore either unrelated, having similar orbital parameters only by chance, or they separated some time prior to 30,000 yr ago and have been inactive (asteroidal in nature) since then.