The Swiss cheese texture on Mars’ south pole is getting holier – so fast that the cheese will soon be gone.

Earlier this week, Shane Byrne, of the University of Arizona in Tucson, presented a model that explained the strange ice dynamics observed by HiRISE. At the south pole, there’s a thin layer of water ice overlain by a layer of frozen carbon dioxide ice that varies in thickness between two to 10 metres. There are pits in the dry ice — the so-called Swiss cheese textures — that tunnel down to the water ice. And observations have shown that the pits are growing.

Once they start to grow, the reflectivity of the dry ice is reduced, more heat is trapped, and the process accelerates. Some have proposed that Mars’ climate is changing. But Byrne asks the question: How can a residual carbon dioxide cap, with these pits, survive for us to observe? The process is so fast that we’d have to be awful lucky to observe the changes.

Byrne ran a model that doesn’t need to invoke any climate change. He starts with a very thin layer of dry ice with a certain degree of roughness. At first, the layer is smooth enough that reflectivity is high, and each winter, more ice condenses. But as the ice layer grows, its roughness increases. After about 30 years, instabilities occur in places with the highest slopes. Pits begin to form. Even as the pits grow, the overall height of ice table grows for while in the intervening flat areas.

But eventually, a tipping point is reached, and all the carbon dioxide disappears. At that point, a smooth, flat film of dry ice could condense to start the process all over again. The whole process, Byrne argues, is the inevitable consequence of starting with an ice surface that isn’t perfectly flat.