By Ron Cowen
On July 1, a dust cloud emerged from Mars’ Hellas Basin, a crater that ranks as one of the biggest in the solar system. Just 3 days later, the cloud had become 1,800 kilometers wide, roughly one-fourth the Red Planet’s diameter.
Two years ago, a similar cloud from Hellas Basin grew until it circled the entire planet, blurring Mars into a featureless orange ball (SN: 11/10/01, p. 299: Available to subscribers at After a martian dust storm). Such planetwide dust storms are rare.
Martian dust storms are powered by solar heating, which whips up the winds that lift dust off the ground. On Aug. 27, Earth and Mars will be closer than they’ve been in nearly 60,000 years, enabling astronomers to make higher-quality observations of the Red Planet than usual. A few days later, on Aug. 30, Mars will reach its closest approach to the sun. For several weeks before and after that time, the amount of sunlight striking the planet will be about 20 percent more than average.
“This means the season for dust storms is just beginning,” says James Bell of Cornell University. But he adds that the two spacecraft now orbiting the Red Planet–the Mars Global Surveyor and Mars Odyssey–have demonstrated that localized dust storms happen “all through the Martian year.”
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