The Battle of Mare Erythraeum was a battle where UNSC Army forces led by Colonel James Ackerson fought the Covenant Loyalist Forces on Mare Erythraeum on the surface of Mars. It was presumed that the UNSC forces were defeated, as Colonel Ackerson was taken prisoner after the engagement. It was possible that other Humans were taken as prisoners, but this is highly unlikely. The fate of Mars after the battle remains unknown.
Ackerson's work in this battle helped buy UNSC ground forces on Earth precious time.