In 1999, a team of astronomers proposed that a gigantic planet — perhaps four times the mass of Jupiter — could be lurking unseen in the Oort cloud, a repository for icy bodies at the edge of the solar system.

The researchers said the presence of this hypothetical planet could explain the unusual orbital paths taken by some comets from the Oort cloud. The planet, which they named Tyche, could have escaped detection to this point by being so far away — perhaps 30,000 times farther from the sun than

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