Here is an overview of the expansion, via Activision:
Destiny 2 Expansion I: Curse of Osiris continues your Guardian’s journey with all-new story missions and adventures set in a new destination, Mercury. Journey through time and space to learn the secrets of Osiris, avert a dark future, and rebuild the ties between the legendary Warlock and his greatest student – Ikora Rey.
Watch the trailer below. View a new set of screenshots at the gallery.