There will be planned maintenance of Destiny's servers today in preparation for a patch preceding the upcoming Rise of Iron DLC.
Rise of Iron is less than two weeks away and, as with all DLC, a patch is coming prior to the launch, and that is today.
At 8am PT, 11am ET, 4pm BST, and 5pm CEST the servers will go down and you won't even be able to log-in. Good news, though, as you should be able to access them again by 4pm PT, 7pm ET, 12am BST, and 1am CEST (Friday). Between these times the 2.4.0 patch should begin pre-downloading and some may have to download another small patch after the servers are online again.
Rise of Iron will be released on September 20 for PS4 and Xbox One.