NASA Scientists have been using the Curiosity Mars rover to examine slabs of rock that have shallow ridges that likely originated as cracks in drying mud more than 3 billion years ago.
Mud cracks would be evidence of a time when dry intervals interrupted wetter periods that supported lakes in the area.
“Mud cracks are the most likely scenario here,” said Curiosity science team member Nathan Stein. He is a graduate student at Caltech in Pasadena, California, who led the investigation of a site called “Old Soaker,” on lower Mount Sharp, Mars.
“Even from a distance, we could see a pattern of four- and five-sided polygons that don’t look like fractures we’ve seen previously with Curiosity,” Stein said. “It looks like what you’d see beside the road where muddy ground has dried and cracked.”
The slab of rock bears a network of four- and five-sided polygons about half an inch to 1 inch (1 to 2 centimeters) across, which matches the pattern commonly formed when a thin layer of mud dries.
Some ridges of material are the same color as the surrounding rock. This could result from a three-step process after cracks form due to drying: Wind-blown sediments accumulate in the open cracks. Later, these sediments and the dried mud become rock under the pressure of multiple younger layers that accumulate on top of them. Most recently, after the overlying layers were eroded away by wind, the vein-filling material resists erosion better than the once-muddy material, so the pattern that began as cracks appears as ridges.