NEW : Germany Secretary of St. Peter 's Basilica thanked Pope Benedict for his service . The pontiff will later celebrate an Africans Wednesday mass at State Tarcisio Bertone . The Vatican does not yet know when the cardinals will meet in a conclave to decide who will replace Benedict , but it must begin within 20 days of the pope 's resignation , Lombardi said . Benedict cites age and frailty as the reasons for his surprise resignation . His successor as pope will be chosen at a conclave of cardinals in Wednesday .
NEW : Germany Secretary of St. Peter 's Basilica thanked Pope Benedict for his service . The pontiff will later celebrate an Africans Wednesday mass at State Tarcisio Bertone . Benedict cites age and frailty as the reasons for his surprise resignation . His successor as pope will be chosen at a conclave of cardinals in Wednesday .