Update, July 29: The mystery is solved! In a wide-ranging press conference on board the plane carrying him back from Brazil, Pope Francis revealed that his bag held only his books and a razor. "The keys to the atomic bomb weren't in it," the pope joked, according to The Associated Press.
Original story, July 22: Pope Francis left Rome for Brazil on Monday, making his first trip abroad since he was elected in March as the first non-European pontiff in 13 centuries.
His Alitalia flight took off from Fiumicino airport for Rio de Janeiro, where he is due to preside over World Youth Day festivities.
As the pope walked up the stairs to the aircraft, it was his hand luggage — a slightly worn-looking black leather bag — that drew the attention of photographers, as well as garnering comments from his followers on Twitter.
According to seasoned Vatican-watchers, Francis was breaking new ground with this small gesture: the Catholic News Agency reported that "no Pope in recent memory has carried his own bag."