https://www.gamespot.com/articles/destiny-2s-first-dlc-pack-will-reportedly-open-the/1100-6452999/

Destiny 2 is not even out yet, but we're already getting information about its upcoming DLC. According to a report from Kotaku, the first DLC pack will add a patrol zone on Mercury, a social space, and a storyline centered around Osiris.

Details of the DLC pack, apparently called The Curse of Osiris, were leaked to Kotaku today. According to the report, the pack will focus on parts of Destiny's lore that have only been hinted at up until now. As the title of the expansion suggests, it has to do with Osiris, an exiled Warlock known for his zealous studies of the Darkness. Specifically, players will be tasked with saving Osiris from the Vex.