While it was announced, just as every other appointment, by the apostolic nuncio in Washington and the pope in Rome simultaneously, this appointment didn't have quite the same dropped-out-of-the-sky feel as some in that it was preceded by another announcement last fall, naming Bishop Quinn, then an auxiliary bishop of Detroit, as Bishop Harrington's coadjutor.
In other words, it was just a matter of time before the torch was passed.
This is only clear, however, if coadjutor is already conveniently part of your vocabulary, which for the many of us, it isn't. But one of the charming aspects of Catholicism is the endless potential for learning, either through history, prayer and reflection, or the endless layers of church concepts and terminology.
The USCCB's online glossary of Catholic terms defines coadjutor:
A bishop appointed to a Catholic diocese or archdiocese to assist the diocesan bishop. Unlike an auxiliary bishop—see auxiliary bishop—he has the right of succession, meaning that he automatically becomes the new bishop when the diocesan bishop retires or dies. By canon law, he is also vicar general of the diocese. If the diocese is an archdiocese, he is called coadjutor archbishop instead of coadjutor bishop. In recent years a growing number of U.S. bishops in larger dioceses or archdioceses have requested and received a coadjutor in the final year or two before their retirement, in order to familiarize their successor with the workings of the (arch)diocese before he has to take over the reins.Seems simple enough.
A couple other random facts worth noting: the Catholic Church in the U.S. has one other coadjutor at present, Coadjutor Archbishop Dennis Schnurr of Cincinnati (formerly bishop of Duluth), who has the right of succession when Archbishop Daniel Pilarczyk retires. Also, prior to the 1983 Code of Canon Law, Rome could distinguish between a coadjutor who had the right of succession and one who did not. This distinction does not exist in the current code, as canon 403, paragraph 3 plainly states, "... a coadjutor bishop does possess the right of succession."