Oort Cloud: A spherical shell around most stars
containing numerous small bodies of cometary material. A typical Oort cloud
is about 0.5 to 1 light year from its primary and has an aggregate mass
about that of Terra; density is
thus extremely low. The main constituents of cometary bodies are ice and
dust ("dirty snowballs"). Bodies in the Oort cloud are occasionally perturbed
by collisions or by the influence of nearby stars into orbits which pass
near the star; these form the visible comets. The Oort cloud is named after
its discoverer, Terran astronomer Jan Oort. -ld
IE