Xbox Live: Halo 3 expansion coming, possibly on Jan 6, 2009

Xbox Live is reporting, "High action and deep mystery await players in this new Halo 3 campaign experience. Prepare to drop!" — looks like that mystery is solved. Additionally, Joystiq tipster Kyle C has found a date hidden in the teaser for Tuesday January 6, 2009 – see the photographic evidence after the break.