Last year, on March 7, the Mars rover Spirit took an image of a streak in the Martian sky. It looked like a meteor trail, but it might also have been an older probe like Viking still orbiting the Red Planet. Scientists weren't sure.
Now they are. The streak was the trail from a meteor burning up in the thin martian atmosphere. It was probably originally part of the comet Wiseman-Skiff, which takes about 6 years to orbit the Sun. Comets are big chunks of frozen gas and rock, and when they get near the Sun the frozen gas sublimates, or goes right from a solid to a gas. The little bits of rock frozen in the matrix then work their way free, and follow in roughly the same orbit. When a planet plows through the debris, you get a meteor shower.
Evidently Mars had a shower of its own in March, and Spirit just happened to catch one of those bits of rock as it made its last hurrah.
Sometimes, those bits of jetsam make their way to the ground. They're called "meteorites" then... and Mars has one of them too! Opportunity found a meteorite on Mars in January 2005, though that one is probably made of iron, and so it came from a denser asteroid, not a comet. Still, that's cool. Opportunity found small craters, too. And the rovers are still going! I wonder what else we'll see in the coming weeks and months.