Why is Comet ISON linked to doomsday, End of the World 2013 prophecy talks?

Nostradamus reportedly made a prediction that "the pope to replace Benedict XVI will 'flee Rome' in the month of December, at a time when the sky has two suns." This is connected to earlier rumour-based speculations that Pope Francis, the 266th and current pope of the Catholic Church, will be the last pope to be named.http://au.ibtimes.com/articles/473831/20130603/comet-ison-2013-doomsday-end-world-prophecy.htm#.Uaw93dJM-xA