Heroic Mode for the Destiny: Rise of Iron "Wrath of the Machine" Raid will go live on October 18th. Bungie Community Manager Deej also revealed on the forums that Challenge Mode will follow soon thereafter. Said Deej, "Ou[r] next challenge is the Heroic Raid. Beyond that, the Raid Bosses will issue some challenges of their own."
Challenge Mode was introduced in The Taken King and required you to take down one of the bosses in the King's Fall raid in a specific manner. Doing so would reward players with very exclusive gear. How Challenge Mode will be applied to Wrath of the Machine remains to be seen as the mechanics of this raid are vastly different from King's Fall.
In the Heroic Mode being released next week, expect to face enemies in greater number who are tougher to kill and much more aggressive. These new additions should tide players over until Festival of the Lost (October) and Sparrow League Racing (December) return to cap of Destiny Year 2.