ROME — The conclave to select a successor to Pope Benedict XVI is scheduled to begin Tuesday, with cardinals gathering in St. Peter’s Basilica for a morning Mass before the afternoon start of the historic session.

The announcement Friday from the Vatican gave a sudden jolt of momentum to the atmosphere here following days of uncertainty, during which cardinals from around the world trickled in to Rome and began a series of confidential meetings to talk about the future of the church.