From Halopedia, the Halo wiki
Topography and ecology
Some survivors of the Battle for Arcadia resettled Abaskun. This community provided the Inner Colonies with much needed foodstuffs until the colony was attacked again by the Covenant in 2549 and the continent was glassed.
Mu is most likely named after a mythical lost continent of Earth legend, which has been variously placed in the Atlantic or Pacific oceans.