June 3, 2009--Spring thaw in Mars's south polar region has revealed mysterious "spider" features under the receding ice cap, seen as a polygonal pattern in a new image taken by the Mars Reconnaissance Orbiter.

Scientists are not sure how such polygons are formed. It's also unclear what created the inky fans of material that decorate the spiders. One theory is that the black marks are debris that erupted from under the Martian surface in a geyser-like process.