Curiosity Found a Sea of Honeycomb Fractures on Mars. Nobody Knows How They Got There.
Curiosity photographed the largest field of honeycomb-shaped polygonal fractures ever seen on Mars during June observations in Valle Grande, a valley where the features spread in every direction — leaving scientists unable to say how they formed.
Curiosity has spent more than a decade crawling across Mars, but the view it recorded on June 19–20 was new even to the scientists driving it. The rover captured a panorama of hundreds of polygonal fractures spreading outward across a Martian valley called Valle Grande, and the scene unfolded in every direction from that same core formation. The fractures are each roughly 1.5 to 3 inches across — or 4 to 8 cm — and the patterns wrap around a small butte the team is calling Miraflores.
Project scientist Ashwin Vasavada put it simply: “a ‘sea of polygons took our breath away’”. Mission scientists have never before encountered so many polygonal formations in one location on Mars. What Curiosity photographed is the largest known field of such formations on the planet — a landscape that appears to stretch unbroken to the limits of what the rover’s cameras could capture.
The shape these fractures make is familiar to any geologist who has studied polygonal patterned ground: networks of ridges and cracks that form polygonal cells on surfaces from Arctic permafrost to dry lake beds. On Mars, Curiosity’s earliest observations of polygonal formations were attributable to mud cracking during ancient cycles of wet and dry conditions. But the Valle Grande features resist that same clear-cut explanation.
Scientists can point to several candidate origins for the formations — ancient mud fractures, temperature cycles, or the sort of compaction that squeezes water upward out of buried sediment — but none has been confirmed. What’s driving the uncertainty is that the new features appear to have formed through a different process than the clearly water-related cracks documented earlier in the mission.
A single panorama assembled from individual photographs stitched into a continuous 360-degree view is what allowed the team to see the scale of the field at all. Without that context, a rover rolling through one cell at a time might never have grasped the extent of what it was crossing. The possibility that the polygons formed through compaction of buried sediment is one of the explanations mission scientists are now weighing — it would point to a subsurface history considerably different from what surface geology alone suggests.
The discovery arrives in the same year that Curiosity detected more than twenty organic compounds never before found on Mars in sandstone formations it had been analyzing — some of them precursors to the molecular building blocks of life. Whether the honeycomb fractures and the organic chemistry are connected remains unclear, but together they are filling in a picture of a planet whose geological and chemical past turns out to be substantially richer than long assumed.