18 January 2013
Venue: GO Jones UG1
** N.B., new venue for the seminar: the seminar will be in UG1 spring term of 2013. **
Asteroids larger than a few hundred metres are commonly described as rubble piles or large assemblages of material held together by their own self gravity. As a result, there is a limit to how quickly these objects can rotate before the inertial forces acting to pull the body apart overcome the gravitational forces holding it together. We know that the YORP effect is capable of increasing the rotation rate of an asteroid and as a result can push it beyond its critical spin limit. The asteroid can then undergo rotational fission. It is becoming clear that this is a natural and fundamental part of an asteroid’s physical evolution which leads to the formation of binary asteroids.
Not all binary asteroids are stable. If the mass ratio of the components of a binary asteroid is smaller than 0.2, the components can decouple from their mutual orbit resulting in two asteroids with very similar but independent heliocentric orbits. Recently a large number of pairs of asteroids have been discovered which appear to have very similar orbits. Backwards integrations of their orbits has shown that the asteroids in each pair have had recent, close encounters, strongly suggesting that these pairs are the remnants of binary asteroids which have subsequently decoupled.
We have begun an optical/NIR spectroscopic survey of the asteroids in each pair to determine whether or not they share common compositions, as would be expected if they formed from common parent bodies. We are also performing new dynamical simulations to better explore the dynamical history of these objects in an effort to refine their formation age. The data we are collecting will allow us to explore the physical evolution of asteroids, especially the process of rotational fission, in greater detail than previously possible.