Hold on. I’m not sure if that 125 million miles in 2021 is correct. According to that chart I linked to, it’s at that same exact distance every time it makes a “close approach”, including this recent one (Dec 2015) where the posted article says it’ll come to within 6.7 million miles. So that number I provided obviously can’t be correct.
It’s that danged Yarkovsky effect! It’ll get you every time. Must be a Soviet trick, all part of their plan to steal our vital bodily fluids.