about noon, after the popemobile left st. peter s square, suddenly, on his twitter account, appeared this, if only everyone could experience the joy of being christian, being loved by god, who gave his son for us. now, his last tweet will come tomorrow, and then after that that twitter account goes silent until a new pope is chosen and if that pope chooses, he, too, can use the handle @pontifacts. msnbc will have continuing coverage of the pope s final day, the resignation all day today and tomorrow, including that final meeting he will have with the cardinals and his official departure from the vatican. up next, it s a bird, it s a plane, no, it s a rock the size of half a football field hurtling towards earth at speeds of over 17,000 miles per hour. we re taking a deep dive into the threat of objects falling from the sky and whetherw should