Krosi-Aspai-Core

Krosi-Aspai-Core, sometimes just called Krosi-Aspai, was the homeworld of the Kroton Absolute, who evolved from a form of quasi-organic tellurium-based crystal that came in contact with servo-robots.

The planet was in Mutter's Spiral, and received its name from a fallen empire. When Krosi-Aspai was attacked by the Metatraxi, it took over four thousand Krotons to lift the First Lattice into orbit. (PROSE: Alien Bodies)

Two Krotons crashed on the Gond planet and attempted to transfer their Dynatrope back to their own cosmos and their own planet, but were defeated by the Second Doctor to protect the Gonds. (TV: The Krotons)

Behind the scenes
The Krotons mention of their "own cosmos" is likely a use of the antiquated scientific terminology that referred to galaxies as "island universes."