Oort Cloud

The Oort Cloud (aka Öpik-Oort Cloud) is the name given to distant long-period comets, along with other such icy bodies at the same distance that are in less-eccentric orbits that don't bring them within our view or that lack the position/velocity combination of a solar orbit. This cloud is presumed to stretch from on the order of 2,000 AU, which is far beyond the planets and the edge of the heliosphere, to a light-year or more from the Sun (one cited further edge being 200,000 AU, which is about 3 light-years, 3/4 the distance to Alpha Centauri). These distances are so far from the Sun that any encounter by the comet with another body (such as with a passing star; some stars are observed to have future or have had past encounters closer to the Sun than Alpha Centauri's current distance) would significantly change the comet's orbit, or easily remove it from a solar orbit, or put such a drifting comet into a solar orbit. Such a set of objects is presumed to exist because the long orbits of long-period comets would spend so much time there (tens of thousands of years), and would be so easily changed, and very unlikely to maintain their observed orbit for as long as do solar system planets (billions of years). Based upon the range of orbital inclinations of long-period comets, the Oort cloud is clearly spherical rather than hugging the ecliptic, as does the much nearer Kuiper Belt. One presumes at least some other stars have such clouds though we don't have the direct evidence of observing their long-period comets, and it could well be that the logical far edge of the Oort cloud is the distance at which a floating comet is more likely to be nudged into an orbit of another star rather than the Sun.