Comet passing by the Earth, illustration. The passage of a large astronomical body near the solar system could disrupt the Oort Cloud, where comet nuclei are thought to reside. The disruption could send comets towards the inner solar system, threatening Earth. 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.