“Global dust storms occur on average only three times per Mars decade,” says Claire Newman, a planetary scientist at Aeolis Research in Arizona. The dust storms are, in a word, baffling. Yet we’re still not sure where the Martian dust comes from-and how it spreads. And the dust sticks to everything, posing threats to current robotic explorers and-in the future-to humans during their long stays on Mars. But the dust event would foreshadow one of the biggest challenges of exploring the Red Planet in the ensuing decades: Martian dust is everywhere-it periodically engulfs the entire planet and evidence suggests that some of it even streams into interplanetary space. Happily, after a few months, the dust cleared, and Mariner 9 began mapping the surface, discovering evidence of past water and the giant canyon system Valles Marineris. The spacecraft had arrived during the most severe dust storm seen on Mars in 70 years of telescopic observation. Mariner 9’s first images showed a planet completely hidden by a bland murk of dust, except for the peaks of a handful of large volcanos. This latest endeavor, however, would photograph the entire surface of an alien world.īut Mars would hold onto its mysteries for a while longer. Earlier flyby missions had yielded brief glimpses of the Red Planet. Just over 50 years ago, NASA’s Mariner 9 arrived at Mars, becoming the first spacecraft to orbit another world. Massive dust storms periodically blanket the Red Planet-and we’re still not sure why.
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