Sometimes large bodies leave the asteroid belt. Is there a danger of one of them colliding with the Earth? Such a scenario is not impossible. This is why teams of scientists track known asteroids that are potentially dangerous. In this way, they can calculate their trajectories and predict a possible impact. Unfortunately, "intruders" sometimes slip through, causing commotion in the scientific community and the media. The 0.9-metre telescope at the Steward Observatory on Kitt Peak in Arizona, USA, is devoted exclusively to hunting down stray asteroids for the Spacewatch Project.