https://www.gamespot.com/articles/destiny-2-nightfall-guide-savathuns-song-strike-mo/1100-6453740/

Bungie has rolled out the latest weekly reset for Destiny 2, which soon see some server downtime and the release of a new 1.0.3.1 update. Among other things, the weekly reset means a new Nightfall is now available, complete with another set of modifiers, Challenges, and rewards.