This new expansion is coming on September 17, 2019, but you can learn more about it now by watching the Destiny 2: Shadowkeep Reveal Trailer.
In Destiny 2: Shadowkeep you return to the moon and journey deep into a mysterious enemy citadel where you help Eris Morn slay nightmarish powers that once slumbered beneath the lunar surface.
Watch the Destiny 2: Shadowkeep – Reveal Trailer from Bungie:
New Nightmares have emerged from the shadows of our forgotten Moon. Called forth by haunting visions from her tormented past, Eris Morn has returned and unleashed something that once slumbered beneath the lunar surface – a long dormant power even she cannot control. Return to the Moon. Journey deep into a mysterious enemy citadel. Help Eris slay these nightmares before they reach out beyond the Moon to cast humanity back into an age of darkness.