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Comets that spend most of their time in the Oort cloud are members of the Oort cloud. Numerous such comets have been observed when close to the Sun. The closer an object is to the Sun the faster it needs to move to maintain the orbit. Objects move slowest when furthest from the Sun (aphelion) and fastest when closest to the Sun (perihelion) and this is why Oort cloud comets spend most of their time in the Oort cloud. While in the Oort cloud these objects are subject to numerous small perturbations that can make notable changes to the orbital period and/or make the object unbound/bound.