Despite the apocalyptic potential of asteroids and comets, Horner’s research suggests we’re more likely to find habitable worlds elsewhere in the galaxy. He says that the presence of a gas giant planet isn’t as important as everyone thinks, and that means there is greater wiggle room in our definition of what makes a solar system habitable. He also theorises that impacts may not always be detrimental to life -- in fact, they may be essential. “It may be that if you have too few impacts, life will stagnate,” he says. “It may even be that our Earth is not the ideal in terms of intelligent life evolving. Maybe we have too few impacts, which is why it’s taken us four and a half billion years to get here.”