Danish astronomer Jan Oort proposed that comets reside in a huge cloud at the outer reaches of the solar system, far beyond the orbit of Pluto. This has come to be known as the Oort Cloud. Statistics imply that it may contain as many as a trillion comets and may account for a significant fraction of the mass of the solar system. However, since the individual comets are so small and so far away, we have no direct evidence about the actual existence of the Oort Cloud.

WHERE DO COMETS COME FROM?