A colony planet whose settlers die of extreme old age after a comet's radiation, which also ages the Enterprise landing party in The Deadly Years.
Gamma Hydra IV is home to a small scientific colony visited by the Enterprise for a routine supply call in The Deadly Years. The landing party finds the colonists dead or dying of advanced old age, though they were young people only days before.
The cause is radiation left by a comet that passed through the system. Kirk, Spock, McCoy, Scott and others begin aging rapidly, while Chekov, who was frightened by finding a body, is spared. That clue leads to a treatment based on adrenaline.