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2006 Nature Publishing Group Hit-and-run planetary collisions

Summary:  2006 Nature Publishing Group
Hit-and-run planetary collisions
Erik Asphaug1
, Craig B. Agnor1
& Quentin Williams1
Terrestrial planet formation is believed to have concluded in our Solar System with about 10 million to 100 million years
of giant impacts, where hundreds of Moon- to Mars-sized planetary embryos acquired random velocities through
gravitational encounters and resonances with one another and with Jupiter. This led to planet-crossing orbits and
collisions that produced the four terrestrial planets, the Moon and asteroids. But here we show that colliding planets do
not simply merge, as is commonly assumed. In many cases, the smaller planet escapes from the collision highly
deformed, spun up, depressurized from equilibrium, stripped of its outer layers, and sometimes pulled apart into a chain
of diverse objects. Remnants of these `hit-and-run' collisions are predicted to be common among remnant planet-forming
populations, and thus to be relevant to asteroid formation and meteorite petrogenesis.
Recent modelling1
shows that for the random velocities expected2,3
following the initial runaway-oligarchic stage of terrestrial planet
, about half of giant impacts result in no net mass accumu-
lation. In many cases, especially at grazing incidence, the impactor
emerges disrupted (for example, ref. 7) but unaccreted. We focus on


Source: Agnor, Craig B. - Astronomy Unit, School of Mathematical Sciences, Queen Mary, University of London


Collections: Physics