For original images go here and here.

Cool image time! The two pictures to the right, cropped and reduced to post here, were taken more than two decades apart by the high resolution camera on Mars Reconnaissance Orbiter (MRO). The show a specific spot on the Martian south pole ice cap, at a location where there is also a perennial cap of dry ice that is also slowly shrinking in size.

The top picture was taken on May 14, 2007, the first close-up of this location. At the time the science team titled it “Fast Evolution of Landforms on the Southern Residual Caps,” which suggests that even then they had a sense from one earlier MRO picture that these strange forms were changing. As a result, scientist have used MRO to monitor this site repeatedly over the years, taking dozens of images of this location on a regular basis to track changes, both seasonally and over years.

The bottom picture is the most recent, taken on May 3, 2026. If you compare the two pictures closely, you can see that all these depressions have grown in some manner over the past two decades. (The blobs you see are all depressions. Optically your mind might make them appear as humps, but they are actually places where the cap’s top layer of dry ice has sublimated away.)

The red dot on the overview map to the right marks the location, deep inside the thin but permanent dry-ice cap at the south pole that sits on top of a larger water-ice cap. The data from MRO and other orbiters say that this dry-ice cap has been slowly shrinking during the decades we have been monitoring its existence.

That it exists at all however is a mystery. The north pole does not have a permanent dry-ice cap. Instead, it like the south pole gets a temporary thin mantle of dry ice every winter, as the carbon dioxide in the atmosphere falls as snow with the coming of colder temperatures. When spring comes however this mantle sublimates away, the CO2 returning to atmosphere as gas.

For reasons that are not yet understood, though they are probably partly related to the higher elevation of the south pole, there remains a permanent dry-ice cap there that the north pole lacks. The data however is telling us that this dry-ice is slowly going away. The two pictures above illustrate this fact.