Comet Siding Spring: Near Miss!
Comet Siding Spring (C/2013 A1) will make a close flyby of Mars on 19 Oct 2014. This close encounter is 10 times closer than any other comet has ever flown past Earth. This flyby will deliver opportunities for learning about comets, but also poses possible risks for orbiting spacecraft. NASA is preparing for both opportunities and challenges.
More info at: http://mars.nasa.gov/comets/sidingspring/