A planet with an unmanned Federation monitoring post from which the Ferengi stole a T-9 energy converter in 2364, prompting the pursuit that led to first visual contact with them.
Gamma Tauri IV is a planet on which the Federation maintained an automated monitoring post. It is mentioned in the first-season Next Generation episode The Last Outpost.
In 2364 a Ferengi vessel removes a T-9 energy converter from the post. The Enterprise-D is ordered to recover the device and chases the Ferengi ship across several systems, an opportunity Picard welcomes because no one in Starfleet has yet seen what a Ferengi looks like.
The chase ends at Delphi Ardu IV, where both ships are held fast by an energy-draining field from an outpost of the long-dead Tkon Empire. Only after Riker satisfies the outpost's guardian, Portal 63, are the ships released, and the Ferengi commander then agrees to return the converter.