Probes were launched everywhere across the Galaxy to search for the relocation of the Rebel base, and (in Darth Vader's mind) to find Luke Skywalker, Darth Vader's son, and what remains of his chance to know his family. One fateful Imperial probe landed on Hoth, and detected a settlement. Darth Vader was convinced that this was the Rebel base, and instructed his ship Executor, among other Star Destroyers, to head for the system.