A Federation-aligned planet threatened in 2368 by an asteroid that the Enterprise-D destroyed, unknowingly picking up metal-eating nitrium parasites in the process.
Tessen III is an inhabited planet featured in the fifth-season Next Generation episode Cost of Living.
In 2368 an asteroid on a collision course is about to strike the planet. The Enterprise-D breaks up the body's core just in time, and the crew think no more about it. However, a glittering cloud from the debris follows the ship and slips inside. It consists of microscopic parasites that feed on nitrium, an alloy used throughout the ship's systems, turning it to jelly.
As replicators, transporters and finally life support begin to fail, Data, who needs no air, takes the ship to the Pelloris Field, an asteroid belt rich in nitrium, and draws the parasites out with a modified beam. The crisis unfolds while Lwaxana Troi prepares for a wedding aboard and takes young Alexander under her wing.