Oort cloud

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Oort cloud A spherical zone surrounding, but gravitationally bound to the solar system, at distances between 20 000 and 100 000 AU from the Sun, which contains about 1012 comets. Its existence was first proposed in 1950 by the Dutch astronomer, Jan Hendrik Oort (1900–92). Gravitational perturbations by passing stars or molecular clouds result in comets acquiring orbits within the orbit of Jupiter.

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