|Notable facts:||Birthplace of John-117|
The Eridanus system is a planetary system in the Outer Colonies in FLEETCOM Sector Four. The system is home to 12 planets, and an orange star known as Eridanus.[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.
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. A large number of 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. It remained a place of much hostility against the UNSC, as Dr. Catherine Halsey stated many pirates and rebels were operating from the system.
The boy who would become the legendary Master Chief was conscripted here in 2517. In 2525, a group of SPARTAN-IIs led by John-117 entered the system aboard the Destroyer UNSC Pioneer. They boarded the cargo freighter Laden, traveled to the rebel base and captured Watts.
The system's main planet, Eridanus II, was glassed by the Covenant in 2530 and the UNSC abandoned the system. 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.
 List of appearances
- ^ 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 "Eridanus" is simply a name given to one of the stars within the constellation. A number of orange, K-class stars in Eridanus are situated within humanity's sphere of influence, including 82 Eridani, at 20 light years from Earth and Delta Eridani, at 29 light years from Earth.