In which decade did Jan Oort develop the hypothesis for this distant reservoir?
Answer
The 1950s
Jan Oort developed the hypothesis in the 1950s after observing that long-period comets seemed to cluster in their orbital paths, suggesting a distant origin.

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What are Oort Cloud objects primarily characterized as?Approximately how many individual objects are estimated to reside in the Oort Cloud?What tangible evidence confirms the inferred existence of the Oort Cloud?How does the spatial structure of the Oort Cloud differ from the Kuiper Belt Objects?Besides water ice, which volatile ices are core components of Oort Cloud objects?What name is given to the inner boundary region of the Oort Cloud structure?What is the hypothesized extent of the Oort Cloud's outer edge in AU?What mechanism can cause Oort Cloud objects to be perturbed inward toward the Sun?Why are comets originating from the Oort Cloud considered chemically pristine?In which decade did Jan Oort develop the hypothesis for this distant reservoir?