Alnath II is a planet located along the Federation - Klingon border in the Beta Quadrant. The planet was also once home to an ancient civilization.

In 2268, the Vulcan science vessel T'Pau visited the planet with an Andorian expedition. After visiting the planet, the Vulcan crew began acting very erratically, and eventually killed each other.

Shortly after, the crews of the USS Enterprise and the IKS Terror were similarly affected. Together they discovered it was linked to an ancient artifact on the planet. (TOS novel: The Klingon Gambit)

planets visited by the USS Enterprise (NCC-1701) during Captain Kirk's initial five-year mission (2265-2270)
various	Capory
2265	Earth • Draxis II • Tally • Alpha Ortelina VII • Arronus VII • Aldebaran III • M-155 • Mestiko • Tally • Dimorus • Tendar • Archernar IV • Delta Vega I • Miri's homeworld • Starbase 12 • 7348-II • robot planet • Timshel • K-G • Zarta • Metamorpha • Numero Uno • FP-1 • FP-2 • Voodoo planet • Gamma Alpha V • Starbase 8 planet • Pollux II • Dukar • Neesan • Algenib II
2266	Beta IV • Rigel XII • Psi 2000 • Tlaoli IV • Alpha Proxima II • Angira • Exo III • 1324-IV • Canara • Nador • M-113 • Alfa 177 • Planet Q • Benecia • Starbase 11 planet • Theta VII (Rell's world) • Talos IV • Numero Uno • Gateway
2267	Makus III • Beta VI • Janus VI • Omicron Ceti III • Deneva • Ceti Alpha V • Eminiar VII • Babel • Gamma Canaris 527 • Taurus II • Hydra Epsilon III • Ximega II • Perseus Arm planetoid • Starbase 11 planet • Salvum • Grotus • Rifas-L • Amusement Park planet • Heitius VII • Centaurus V • Tyrtaeus II • Gothos • Cestus III • Iron-silica planet • Zutotanium planetoid • Mudd • Earth • Canara • Beta III • Pyris VII • Vulcan • Pollux IV • Argelius II • Halka • Bavarya • Neolithia • Mythra • Capella IV • Magna Roma • Gamma Trianguli VI • Sigma Iotia II • Masaba • Lekythos • Shroud IV • Tycho IV • Donico II • Rimillia • Organia
2268	Narnel's World • Neural • Fornax II • Gamma II • Triskelion • Argus X • Tycho IV • Theta VII • Signi Beta • Earth • Direidi • Eeiauo • Patria I • Leora IV • Academy • Delta Canaris IV • Alnath II • Ammdon • Marcos XII • Amerind • Beta XII-A • Elas • Troyius • Sigma Draconis VI • Ekos • Scalos
2269	Anomaly • Excalbia • Andros • Pollux V • Avalon • Camus II • Tanis • Aleph Prime • Kyros • Viden • Theta Tau V • Aleph III • Trefolg • Mantilles • Merak II • Ardana • Babel • Organia • Gateway
2270	Isitra Zero • Gateway • Mercan • Denebia • Phylos II • Amusement Park planet • Motherlode • Megas-Tu • Terratin • Sherman's Planet • Argo • Vedala asteroid • Dramia II • Arret • Lactra VII • Delta Theta III • Archernar IV • Cenotaph • Taygeta V • Okeanos • Yoondri • Aleriad • Mercan • Aritani • Yalbo • Sycorax • Talos IV • Earth • Starbase 12 • Tomarii