Halo Alpha
Halo Alpha

Not to be confused with the Epsilon Eridani System.

The Eridanus System is a planetary system in the Eridanus sector, in the Outer Colonies. The system is home to 12 planets,[1] and an orange star referred to as Eridanus.[2][note 1] One of the many systems with prevalent Insurrectionist activity, it was under UNSC control until 2530 when its main planet, Eridanus II, was glassed by the Covenant.[3]



The rebels had staged a localized rebellion against the UNSC in 2494. The UNSC struck back two years later and forced the rebels out at the cost of four destroyers. Numerous rebels survived, however, and under the command of the UNSC turncoat Colonel Robert Watts, overthrew the civilian government of the system in 2513. Watts was presumed killed in the UNSC's counterattack, Operation: TREBUCHET, but in fact he escaped to Eridanus secundus in the system's asteroid belt with the rest of the rebels.[4] It remained a place of much hostility against the UNSC, as Dr. Catherine Halsey stated many pirates and rebels were operating from the system.[5]

In 2511, the Freedom and Liberation Party detonated a nuclear bomb on Mamore.[6] The boy who would become the legendary John-117 was conscripted here in 2517. In 2525, a group of SPARTAN-IIs led by John-117 entered the system aboard the Destroyer UNSC Pioneer.[4] They boarded the cargo freighter Laden, traveled to the rebel base and captured Watts.[7]

Human-Covenant war[]

The system's main planet, Eridanus II, was glassed by the Covenant in 2530 and the UNSC abandoned the system.[3] However, the asteroid base survived, and the SPARTANs later returned to the system in 2552 aboard the captured Covenant flagship Ascendant Justice, fleeing from the Battle of Reach to expedite repairs at the Rebel base. However, a Covenant fleet followed and destroyed the base, with only the Ascendant Justice escaping.


As the system was prone to resisting the UEG government, multiple competing government entities existed throughout the system. On Mamore, the Freedom and Liberation Party was fighting for control over the planet.[6] On Eridanus II, a sect of the United Rebel Front was contesting for control. The whole system was within UEG space and was presumably under Colonial Administration Authority jurisdiction. It is unknown under whose jurisdiction the system falls under after the war.




  1. There is no star system by the name "Eridanus" in the real world. However, a constellation of the same name exists, and it is likely that this system is located around one of the stars within the constellation. One possible star would be Eta Eridani, 121 light years away from Earth. With human ships being able to cross distances of 2.626 light years per day, it would only take 46 days to reach Eta Eridani. Another possible star, also within the constellation, would be 82 Eridani, about 20 light-years from Earth. Much like Eridanus mentioned in the novels, the star is orange and is noted as being a possible location for a habitable system.


  1. Halo: The Fall of Reach, page 75
  2. Halo: The Fall of Reach, pages 17 and 21
  3. 3.0 3.1 Halo: First Strike, page 240
  4. 4.0 4.1 Halo. The Fall of Reach, pages 75-76
  5. Halo. The Fall of Reach, pages 17-18
  6. 6.0 6.1 Halo: Reach Limited Edition - Bonus Item: Dr. Halsey's Personal Journal, February 23, 2511
  7. Halo. The Fall of Reach, Chapter 10