What happens when two violent forces – wind and volcanoes – are at work on Mars? NASA’s Spirit Mars rover is having a field day finding out the answer.

The robot’s microscopic imager has relayed this photo of a rock tagged “GongGong” – a jagged mini-landscape. The rock lies in the “Inner Basin” between “Husband Hill” and “McCool Hill” in Gusev Crater.

GongGong formed billions of years ago on Mars, in a seething, stirring mass of molten rock. The molten rock was deformed as it moved across the red planet’s surface. Tiny bubbles of gas trapped within the lava were distorted as well, becoming elongated. When the molten lava solidified, the rock took on the look of a frozen sponge.

Over time, GongGong has undergone blasting from wind-carried sand grains. That sandblasting has worn away the surface until, little by little, the delicate strands that enclosed the bubbles of gas were breached and the rock’s spiny texture emerged as evidenced in this image. The photo was taken late last month, on the rover’s 736th day, or sol, of exploring Mars.

• Special Report: Spirit and Opportunity’s Mission to Mars

-- Leonard David

Credit: NASA/JPL-Caltech/Cornell/USGS