‘You know what Caloris is, right? One vast impact crater. Fifteen hundred kilometres wide. Bear in mind that’s about a third of the planet’s diameter: just one crater. Even beyond the walls there are splashes of debris, rings of heaped-up ejecta, going out hundreds of kilometres. One of the biggest impact craters in the Solar System – and there’s a feature almost as striking at the antipode, where the shock waves from the impact washed around the planet and collided, crumpling everything up. Mercury’s biggest whack aside from the mantle-stripper itself.’
-Xeelee: Vengeance, Ch. 14