Recently a comet has been discovered that will make an uncomfortably close call... to Mars. The comet identified as C/2013 A1 could come within AU (650,000 miles) from Mars on Oct 19 2014 according to current observations. This guy came from the Oort Cloud, a distant region of the outer solar system that contains countless comets.
"C/2013 A1 was discovered by ace comet-hunter Robert McNaught at the Siding Spring Observatory in New South Wales, Australia, on Jan. 3. When the discovery was made, astronomers at the Catalina Sky Survey in Arizona looked back over their observations to find “prerecovery” images of the comet dating back to Dec. 8, 2012. These observations placed the orbital trajectory of comet C/2013 A1 through Mars orbit on Oct. 19, 2014.
Could the Red Planet be in for a potentially huge impact next year? Will Mars rovers Curiosity and Opportunity be in danger of becoming scrap metal."
would be quite the show