The ISS Enterprise orbits the Halkan homeworld
The Halkan homeworld was a planet that was home of the Halkans, and was rich in dilithium.
In 2267, Captain Kirk and some others in the ISS Enterprise crew were trying to force the Halkans to offer the Terran Empire rights to mine the dilithium. When they were denied the crystals, they attempted to transport to their ship in order to punish the planet's pathetic inhabitants, but ion storms on the planet caused a transporter malfunction, which displaced Kirk and the others into an alternate universe. When there, they found themselves on the Federation's USS Enterprise. Spock's counterpart ordered Kirk and the others detained, realizing them not to be "their" crewmates. Spock however, eventually permitted them to return to the ISS Enterprise. (TOS: "Mirror, Mirror")