Asteroid deflection. Computer illustration of a laser being used to deflect an asteroid from its impact course with Earth. This technique would use a laser to heat the surface of an icy asteroid or comet, causing the ice to boil and gas jets to be emitted. These gas jets would act as rockets to propel the asteroid sideways and away from its impact course with Earth. This technique would only work on icy bodies, and not on those asteroids that are mainly iron. Only small changes in the asteroid's course would be needed to make sure it missed Earth.