THE COMMON ROOTS OF ASTEROIDS (6070) RHEINLAND AND (54827) 2001 NQ8

Our previous analysis of the available catalogues of asteroid orbits revealed the existence of pairs of bodies residing on nearby trajectories. Their proximity, far tighter than one would expect from random fluctuations of the distribution in the orbital space, implies that some process(es) disintegrated a common precursor of asteroids in each pair some thousands to hundreds of thousands of years ago. The analysis of these process(es) is of great interest in planetary science. Here we focus on the best characterized paired asteroids—(6070) Rheinland and (54827) 2001 NQ8—and determine conditions of their separation in the past. First, by using a numerical model that ignores asteroids' gravity, we show there is a possibility of an approach closer than 1000 km (radius of their Hill sphere) 17.22 ± 0.28 kyr ago; we interpret this as the origin of the pair. This is the most accurate determination of an asteroid age so far. We also find that the median encounter velocity at infinity is 17 cm s−1, while its component normal to the orbit of larger asteroid (6070) Rheinland is only 21 mm s−1. Second, we model the initial phase of separation of these two bodies by including the effects of mutual gravitational interaction when their distance is smaller than the Hill radius. Our simulations indicate their minimum initial separation may have been comparable to the physical distance of their centers. This is the first time an accurate numerical integration can bring two asteroid fragments into a single point in the past. Resting geometry (when 2001 NQ8 touches Rheinland), close- and distant-satellite initial configurations are all possible, but cannot be discriminated so far.

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