NASA's Curiosity rover has spotted a bizarre-looking network of Martian mineral ridges — and that has piqued the curiosity of the rover's science team. They say the two-tone veins suggest there were separate stretches of time when there were wet conditions in the area that Curiosity is currently studying.

The ridges rise as high as 2.5 inches (6 centimeters) above the level of the bedrock at a site nicknamed Garland City, on the slopes of a 3-mile-high (5-kilometer-high) mountain known as Aeolis Mons or Mount Sharp. They're about an inch (3 centimeters) thick, and are made of light and dark material.

"Some of them look like ice-cream sandwiches: dark on both edges and white in the middle," Linda Kah, a Curiosity team member at the University of Tennessee at Knoxville, said in an image advisory issued Wednesday. "These materials tell us about secondary fluids that were transported through the region after the host rock formed."

Kah and her colleagues say the mud that formed the rock around Mount Sharp must have dried and hardened first. Then the dark material would have been deposited inside cracks in the stone. Later, fluids that were rich in calcium sulfate seeped into the cracks as well, providing the light-colored material for the ice-cream sandwich. Then the surrounding mudstone was eroded away, leaving the ridges behind.

Detailed analysis of the ridges could help Curiosity's scientists piece together Mars' geological history. "We want to understand the chemistry of the different fluids that were here and the sequence of events," Kah said. "How have later fluids affected the host rock?"

Scientists have been guiding the six-wheeled Curiosity rover up Mount Sharp's slopes for months, documenting the mountain's layers in hopes of learning how the Martian environment shifted from wet to dry conditions over the course of billions of years.