Ysida is a sandy planet with a vapor ocean where Captain Chakotay and the Protostar were stranded for ten years.
Ysida is the desolate, sandy world where Chakotay and his first officer Adreek-Hu were marooned with the Protostar after escaping through a rift. Chakotay ejected the ship's antimatter and proto-core, leaving it on emergency power, and after Adreek died gathering antimatter in a storm, Chakotay was left alone.
In Last Flight of the Protostar, Dal and his friends arrive and help the broken captain recover his spirit. They evade giant eels, then turn the Protostar into a makeshift sailing vessel to cross a vapor ocean and collect deuterium from a maelstrom, restoring power and leaving the planet.