A planet being surveyed for its rich tritanium deposits when a deadly gaseous creature attacks the Enterprise landing party in the Original Series episode Obsession.
Argus X is the planet on which the Original Series episode Obsession begins. Kirk, Spock and a security team are surveying deposits of tritanium, an ore many times harder than diamond, when Kirk notices a sickly sweet smell he remembers from his days aboard the USS Farragut.
A gaseous creature attacks the security men and drains the red corpuscles from their blood. Kirk recognises it as the thing that killed Captain Garrovick eleven years earlier at Tycho IV, more than a thousand light years away.
He keeps the Enterprise in orbit to hunt it, delaying the delivery of perishable vaccines and alarming Spock and McCoy. The creature eventually leaves the planet and travels through space, and the chase leads back to Tycho IV.