Dust storms in Mars' atmosphere. Some can be local, regional, or global in scope. Mars's thin atmosphere and low surface gravity can make dust storms more intense than on Earth. Big storms tend to occur shortly after southern summer begins, when Mars is near its closest point to the Sun. When Mars was first photographed, it experienced a global dust storm, obscuring most of the surface except for Olympus Mars and the Tharsis Montes, which rose above the storm. The Mars Odyssey spacecraft is currently monitoring dust conditions on Mars for other spacecraft. Dust can obscure view of Mars from Orbiters and reduce sunlight that strikes solar panels on surface spacecraft (reduced 99% for both rovers in 2007). When the dust settles, it sticks to the solar panels, further reducing their capabilities, but dust devils can later wipe away this dust. A severe dust storm was in 2001 and a more modest one in 2007 and a minor one in 2009.