Episode 24: What happens when two planets collide? The smaller one desintegrates but the bigger one survives, even though some of its characteristics are altered, its chemical compositon for instance. The scope of these alterations depends on a pivotal moment of the collision: the immersion of the core of the smaller planet into the magma ocean formed after the impact, and the subsequent core/magma exchanges. Scientists from Marseilles have recreated this episode in a laboratory. They found that the core, made of liquid iron, behaves differently depending on the difference in viscosity between the iron and the magma.