Mars Is About to Get Visitor That Comes Around Only Once In A Million Years Or So.

NPR- October 19, 2014

The arrival of a “mountain-sized” comet, Siding Spring (C/2013 A1), is made all the more extraordinary by the fact that humans — who were busy refining their stone-tool-making skills the last time such an event might have occurred — now have spacecraft from multiple countries at the Red Planet to see it happen.