In the high latitudes of Mars, the ground is covered by a network of polygonal cracks forming patterns that look, at first glance, like a tiled floor. These features - polygonal patterned ground - are produced by the same process that creates similar patterns in Arctic and Antarctic permafrost regions on Earth: thermal contraction.
How thermal contraction polygons form
In regions where soil contains significant amounts of ice, seasonal temperature changes cause the ground to contract and expand. In very cold conditions, this contraction can be strong enough to crack the ground. The cracks form a network - because stress is roughly equal in all horizontal directions, the cracks tend to meet at approximately right angles, forming a polygonal pattern.
On Earth, these features are found in Alaska, Siberia, Antarctica, and other permafrost regions. Their presence on Mars was one of the early indirect indicators of subsurface ice at high latitudes - later confirmed directly by the Phoenix lander, which scraped the surface and found ice just a few centimetres down.
What the HiRISE images show
HiRISE images of polygonal patterned ground on Mars show the network of cracks at a resolution where individual crack widths are measurable - typically a few metres across. The polygons themselves range from a few metres to tens of metres in diameter. The regularity of the pattern is striking: a tiled surface produced by physics operating uniformly across a large area.
The spacing and size of the polygons carry information about the depth of ice, the age of the feature, and the thermal history of the region. Planetary scientists use these measurements to reconstruct past climate conditions at Martian high latitudes.
The Axisophy print
The Radiance collection includes a HiRISE image of Martian polygonal patterned ground - one of the most geometrically precise natural patterns on the planet's surface. The regularity of the polygon network makes it one of the most graphically striking images in the collection.
