Forming Binary Near-Earth Asteroids From Tidal Disruptions

2.3.5 Triples and hierarchical systemsIn general, triple systems (a system with two secondaries orbiting one primary) are likelyto be unstable on short timescales in the inner solar system. Currently one Main-Beltasteroid has been observed in this state ((87) Sylvia, and its satellites Romulus and Remus).However, the simulations produced these and more complicated systems with N >3. The simplest case of two satellites orbiting the largest remnant was found in 757 of thesimulations with another 357 having three or more satellites in orbit.Some unique situations involved multiple systems formed around the second, third,and fourth largest remnant. There were 5 simulations with at least 2 secondaries aroundthe second largest remnant, 6 that produced them around the third largest, and 1 simulationthat produced them around the fourth largest remnant. These situations almost exclusivelyoriginated from very close encounters (q < 1.6 R ♁ ) and fast-spinning primaries (4 h).A hierarchical system, where a secondary has a bound companion, was a rare outcome.A total of 102 simulations produced these systems. These were typically simplesituations with a satellite bound to the second-largest remnant, which in turn was boundto the largest remnant. Though no similar systems have been observed among asteroids,they do occur immediately post-disruption in simulations.2.3.6 Tidal evolution and eccentricity dampingThe simulations represent snapshots of binary properties immediately after formation.Subject to tidal interactions, planetary encounters, and thermal effects, the binaries willevolve with time. Tidal forces between the primary and secondary will affect the binaryin most cases by: changing the semi major axis of the secondary’s orbit, synchronizingthe secondary’s rotation with its orbital period, and changing the eccentricity of the secondary.Weidenschilling et al. (1989) determined the change of the semi-major axis of a50