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Neil deGrasse Tyson isn't convinced that aliens have visited Earth. » Subscribe to MSNBC: http://on.msnbc.com/SubscribeTomsnbc Follow MSNBC Show Blogs MaddowBlog: https://www.msnbc.com/maddowblog ReidOut Blog: https://www.msnbc.com/reidoutblog MSNBC delivers breaking news, in-depth ...