We tend to forget how much space hardware we have in our cosmic quiver. Now these space science assets are gearing up for a once-in-a-lifetime comet (C/2013 A1) flyby of Mars on October 19, 2014. The comet, also called Siding Spring, will pass within 87,000 miles (139,500 km) of our neighboring planet. This may not seem like a near miss, but to put it into perspective, it is less than half the distance to our moon from Earth.
NASA expects Siding Spring (coming from the Oort Cloud 5,000 - 100,000 astronomical units away and thought to be left from the formation of the solar system) to pass by Mars with little problem, but the debris trail that accompanies comets may be a different story. [NASA rovers Curiosity and Opportunity should be fine and checking out the visitor.] Time will tell.
In any event, we Earthlings and our NASA instrumentation/satellites will have front row seats to the action. Go science!