Cardinals under 80, known as cardinal-electors, can enter a secret conclave to choose a new pope from their own ranks after Francis dies or resigns. Francis, the former cardinal-archbishop of Buenos Aires, was elected in a conclave on March 13, 2013.Nope, that's not right.
Now this is, of course, from an article that addresses Pope Francis having appointed new Cardinals yesterday. Reuters, in this article, attempts explain what that means.
And what it states here is that the Cardinal Electors must choose from their own ranks. They do not have to do that.
The only real requirement to be elected to the Papacy is that the elected figure be a male Catholic, and hence eligible for Holy Orders. That's it. In order to be elected you do not have to be a "Roman" Catholic, only a Catholic (a man from the Eastern Rite could be elected), nor do you even have to be a Priest. You do have take Holy Orders in order to become Pope, so under the wild hypothetical of a non Priest being chosen you would have to see something like what occurred occasionally in the past where a layman was ordained and then elevated to Bishop (in this case the Bishop of Rome) in a single day.
Will that happen? Well, no, its not very likely.
But could the College of Cardinals choose somebody outside their ranks? It's unlikely, but it certainly could happen.