Dust storms can whip up in a hurry on Mars, with the biggest of them covering the entire planet. These two images, for example, show the same view of Mars, but taken just one month apart. In the image on the left, the skies are clear; at right, a global dust storm has hidden most of the planet's features from view. A big dust storm could swirl to life on Mars later this year. [NASA/JPL/MSSS]