Although the event was first planned under Pope Benedict XVI, Chaput appears confident the new pontiff will come.
"Every indication that I have is that he's coming," Chaput said in an interview. "I don't expect a formal announcement until six months" before the September 2015 event begins, he said.
Another purpose of the trip, Chaput said, is to increase excitement back home.
"It boosts us back home in terms of energizing us to be even more committed to pulling this off," he said.
Chaput said he hopes the pope's possible visit would reinvigorate the Archdiocese of Philadelphia, which has been rocked in recent years by the clergy sex-abuse scandal and financial woes.
"We certainly are in need of positive encouragement, and it's certainly going to do that for us," Chaput said. "People who aren't believers talk about wonderful coincidences, and those of us who are believers talk about God's providence. So I think it's a wonderful act of providence that's happening in Philadelphia. We're going to show the world how beautiful the city is."
Nutter and Corbett said another core purpose for this week's trip is planning. The Pontifical Council for the Family organizes the triennial World Meetings of Families, which draw hundreds of thousands of people even without a papal presence.
"It's a necessary step to find out exactly what the Vatican expects from us in regard to the conference and then with regard to a potential meeting of the pope," Corbett said in an interview. "It would mean a great deal for Philadelphia and for the state to be the first location that this pope would visit."
Although the Pennsylvania delegation's invitation is a nice touch, Palmo said it's President Obama who must formally invite Francis, one head of state to another.
As it happens, Obama will arrive at the Vatican on Thursday, just as the local officials are leaving, to meet the new pope for the first time. Queen Elizabeth II will come to the Vatican a few days later, also to formally greet the new pope.
Palmo said the Philadelphia meeting could be one stop on a high-profile trip through the United States.
"It's probably going to be Francis' only trip to the United States," Palmo said of the 76-year-old pontiff.
It's no coincidence, he said, that the 2015 meeting is scheduled right after the United Nations General Assembly begins a session. Usually, the meetings happen during the summer, but the Sept. 22-27 schedule could allow Francis to make an address at the U.N., in New York, after leaving Philly.
Another possibility is that Francis accepts House Speaker John Boehner's recent invitation to speak before a joint session of Congress, as the president does for the State of the Union.
On Twitter: @SeanWalshDN