Mars and the Comet: The Countdown 

On Sunday, Oct. 19, 2014, at about 18:30 UTC (14:30 Eastern), Mars will experience a very close encounter with a comet.  The comet C/2013 A1 (Siding Spring) will pass just about 130,000 km (80,000 miles) from the surface of Mars. There is no danger of an impact, but the planet will pass through part of the comet's tail (which is composed of gas molecules and dust). NASA and other space agencies have taken precautions to make sure the spacecraft at Mars won't be hurt, but they're also hoping to ...