The Jaros System was a star system within Federation space.
The system contained two Class M planets. Jaros II was a marginally Class M world with a hot, dry climate. Starfleet maintained its stockade facility on Jaros II. Those who were incarcerated at Jaros II included Valeris, Ro Laren, and Ezri Dax. (ST novel: Cast No Shadow, TNG episode: "Ensign Ro", and ST - The Fall novel: The Poisoned Chalice)
Jaros II's nearest neighboring planet was also Class M. Unlike Jaros II the climate of that planet was much more temperate, with a wide variety of flora and fauna present (ST - The Fall novel: The Poisoned Chalice)
- The novel The Poisoned Chalice mentioned this second Class M planet, however it did not specify whether this planet was Jaros I or Jaros III.