Comet impact on Earth - HD 影片檔

"Animation of a comet impact on Earth. The impactor is preceded by other comets, which pass harmlessly by. Several comets could be directed towards the inner solar system by a large body passing by the outer solar system, especially the Oort Cloud, where comet nuclei are thought to reside. Some have theorised that the Sun may have a dim companion star (dubbed Nemesis) that regularly perturbs the Oort Cloud, raining comets inwards and causing periodic mass extinctions. No evidence has been found for the presence of such a body, however."