Planet Symphonia is the planet the Zoshlings (Set) came from. The planet has only been mentioned by the Zoshlings as their home. The scientist noticed a new star orbiting the Moshi World and sent the Rhapsody 2 crew to investigate.
The planet is far beyond the scope of Tamara's Telescope. As Captain Squirk wanted to be back for dinner, it suggests the technology of the Rhapsody 2 makes them able the travel at unimaginable speed.