Origin of Comets

The Oort Cloud

Dutch astronomer Jan Van Oort studied the orbits of 19 long-period comets and proposed in 1950 that the comets which are visible from Earth come from a huge comet 'cloud' of perhaps a trillion objects.

From the comets' orbits, Oort estimated the size of this cloud to be about 100,000 astronomical units (AU) in diameter; about half the distance to the nearest stars. By comparison, the orbit of Pluto, is only 40 AU in diameter.