Oort Cloud  Oort cloud is an immense spherical cloud surrounding the planetary system and extending approximately 3 light years, about 30 trillion kilometers from the Sun. This vast distance is considered the edge of the Sun's orb of physical, gravitational, or dynamical...

Planetary Society: Oort Cloud  No one has ever measured its size and density or counted the objects in it. Nor is anyone likely to do so in the foreseeable future: the Oort cloud is too distant, and the objects in it too small and...