An M Class planet near a binary star system in the outer Izar region. It boasted three distinct regions: tropical/temperate, volcanic, and artic. It was highly volcanicly active, with eruptions in both the volcanic and artic zones.

Breathing the natural air on Zeta Sigma made one unable to leave the atmosphere. Attempted departure would result in dizziness, naseau, convulsion, loss of consciousness, and even death. The Doctor Arnet discovered the cause to be a passive virus like particle that attached to one's red blood cells. The body became, in effect, addicted to it and went into withdrawls once it could no longer take in the particle.

During the events of "In the Line of Duty" the Potemkin discovered from orbit a few sparse settlements and ships that had appeared to have crashed on the surface of Zeta Sigma. Deciding to investigate, the ship landed and away team was dispatched, contaminating the ship with outside air.

The away team was found by Danielle Beorning, captain of the Starcore, but she was too late to warn them of the danger. Upon trying to leave, they experienced the withdrawl symptoms and had to land again. The crew was stranded there for nearly two weeks.

Doctor Arnet, who had been in an isolated biochamber at the time, was the only one not infected. Working alone, he found a way to mutate the particle with in his own body and produce an antidote for the crew. However, this meant that he was infected with the same addiction and had to remain behind to discover a cure for himself. Captain Beorning elected to remain behind with him.

In the alternate future of "Here Comes Tomorrow," the future Arnet states that it took him four years to find a permenent cure for Zeta Sigma III's addictive atmosphere.