The planet Mars is in the danger of getting hit by a comet on 19th October 2014 according to new news. This has not yet been confirmed as there is still considerable uncertainty about the comet orbit at current time. There is however the risk of impact. If this comet impacts Mars it is going to change the surface of Mars for centuries, as the impact crater is going to be at least double the size of the comet. This would also create a earthquake (marsquake) with the magnitude of Mw9.5+ on impact.
I am going to post more information on this as they become available.
News and information about this comet
C/2013 A1 (Wikipedia)
Could a Comet Hit Mars in 2014? (Discovery News)