Imagine looking out across a Martian valley and seeing the ground tiled — in every direction, as far as the camera can see — with tiny hexagons. That is exactly what NASA's Curiosity rover encountered while climbing through a valley nicknamed Valle Grande. The shapes, called polygonal fractures, measure just four to eight centimetres across. They are small enough to fit in your palm, yet there are so many of them that scientists are calling the sight a "sea of polygons.

" The full spectacle was captured in a sweeping 360-degree panorama on June 19 and 20, during the 4,930th and 4,931st Martian days of the mission — known as sols. The patterns do not simply cover the flat ground; they also climb the sides of a nearby rocky mound, nicknamed Miraflores, which rises six metres above the surrounding landscape and is capped by a thick layer of sand. Curiosity has glimpsed similar shapes before, but never at anything close to this scale. "We've seen a lot of fascinating landscapes through Curiosity's eyes, but this sea of polygons took our breath away," said Ashwin Vasavada, the mission's project scientist at NASA's Jet Propulsion Laboratory in California.

What made these shapes? Scientists are not yet certain, which is part of what makes them so exciting. Cracking mud is one possibility — the kind that forms when water dries up. But repeated cycles of warming and cooling can also fracture rock into geometric patterns, as can pressure that squeezes water out of buried sediment.

The team is now analysing the chemistry of the formations to separate these competing explanations.