NASA’s Curiosity rover has discovered its largest yet expanse of honeycomb-like polygonal fractures in Valle Grande on Mars. The finding matters because such patterns may preserve evidence about ancient environmental conditions, including whether water once existed in the valley.

Curiosity photographed the “sea of polygons” in a 360-degree panorama on 19 and 20 June, during Martian sols 4,930 and 4,931. Individual fractures measure roughly 1.5 to 3 inches across; scientists are analysing their shapes and chemistry to determine whether they formed through drying mud, temperature cycles, or sediment compression that expelled water billions of years ago.