Mysterious Martian grooves identified

A kilometer long, sometimes more: this is the size that certain dark grooves, known as araneiforms, can reach, scarring the southern polar cap of Mars. These formations, which researchers have nicknamed araneiforms in reference to their resemblance to arachnid legs, are concentrated in a very specific area: the high latitudes of the Martian south pole.

Formation mechanism discovered

The spider-like grooves result from the sublimation of trapped CO2 ice beneath the surface, which fractures the polar cap in spring, according to the Kieffer mechanism. The gas released under pressure carries dust and dark sand that deposit in radial patterns, creating the grooves through the annual repetition of the phenomenon.

Process explained in detail

It all begins during the Martian southern winter, a season of extreme cold where atmospheric carbon dioxide condenses directly onto the ground to form a translucent ice layer. With the return of spring, solar radiation becomes more intense, causing the CO2 ice to sublime directly from solid to gas, creating pressure that eventually fractures the ice layer and releases a jet of gas carrying dust and sand.

Unique Martian phenomenon

This cycle, observed by the Mars Express and ExoMars Trace Gas Orbiter probes, is unique in the solar system because it relies solely on solar energy, without water or hydrothermal activity. What impresses researchers is the speed of the process: some networks form within just a few days to a few months, a remarkable speed on a geological timescale.

Other Martian features nearby

What impresses researchers is the speed of the process: some networks form within just a few days to a few months, a remarkable speed on a geological timescale. These Martian spiders constitute a true natural laboratory for understanding the seasonal cycle of CO2 on the red planet, a cycle that has no equivalent on Earth where known geysers always result from hydrothermal activity linked to the planet's internal heat.