Mariposa
From Halopedia, the Halo wiki
The "Rings of Mariposa" were mentioned in the story 'Second Sunrise over New Mombassa' in the Halo Graphic Novel. It's therefore likely to be a gas giant. At some point in time "the 6th Battle Group outmaneuvered and escaped" what was presumably a Covenant fleet near the planet Mariposa.
