Moon and Mars
 A giant dust storm covered much of Mars earlier this year, threatening the two rovers that have operated on Mars for almost four years. These two images show how the storm progressed. At top, the surface is clearly visible from the orbiting Mars Reconnaissance Orbiter, even though wisps of dust are already showing up, and a thick cloud of dust is visible at top left. (The dark areas are gaps in the camera's data.) At bottom, in a picture of the same region taken four weeks later, almost none of the surface is visible. The Opportunity rover is inside the small white circle in the two pictures. [NASA/JPL/MSSS]
The twin Mars rovers highlighted another hazard earlier this year: dust storms.
As the seasons on Mars change, they can stir up air currents that create dust storms. Within days or weeks, the storms can cover thousands of square miles -- and in some cases, almost the entire planet.
That's what happened in July. A global storm filled the skies with dust. It blocked most of the light from the Sun, so the solar cells that power the rovers weren't producing much electricity. In fact, the Opportunity rover barely survived. Engineers had to turn off its scientific instruments and its radio just so it would have enough power to keep its heater working during the frigid Martian nights.
The storms also coated the solar cells with dust, which continues to limit their power production. There was no one around with a whiskbroom to sweep them off. Engineers found a way to get rid of some of the dust, but not all. That left the rovers with less power for their instruments, reducing their scientific workload.
Mars is shining bright now. It follows the Moon across the sky tonight. It's far to the lower left of the Moon in mid-evening, and looks like a bright orange star. More about Mars tomorrow.
Script by Damond Benningfield, Copyright 2007
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