Oort’s cloud - Reflexions

Oort’s cloud

Oort’s cloud is a vast hypothetical sphere of bodies situated at about 50 000 AU (astronomical units) from the Sun, well beyond the orbit of planets and the Kuiper Belt. The external limit of Oort’s cloud, which forms the gravitational boundary of the solar system, is situated at more than a billion times the distance separating the Sun and Pluto, or around one and a quarter light years of distance from Proxima Centaurus, the star nearest the Sun. Although no direct observation has been made of such a cloud, astronomers, basing their theories on analysis of the orbits of comets, generally think that it is the reservoir of long period comets. This cloud takes its name from the Dutch astronomer Jan Oort who came up with the hypothesis for its existence in 1950, by statistically studying fifty cometary orbits.