Mars is on coalition course with comet 2013 A1 said NASA

A 1.5 miles diameter comet name 2013 A1 is heading for Mars, and there is a chance that it might hit the Red Planet in October 2014. An impact would not necessarily mean the end of NASA's Mars program. But it would transform the program along with Mars itself.

And if Comet 2013 A1 would hit Mars ground it would maybe transform Mars into a warmer and witter planet and terra-forming Mars will be much more interesting than ever.

If it happens to collide with Mars it would blow an equivalent of 35 millions tons of TNT from its current calculated speed of 125,000 miles per hour. And the effect of impact in comparison to that hit on Earth long time ago that wiped out the dinosaur is one-third.