Why is Mars' Southern Polar Cap Crooked? | Universe Today
This is why the southern ice cap of Mars is off to the side of the south pole during the summer there. The 2300 km wide Hellas impact basin has winds blowing into it that causes a high pressure area and a low pressure area in the atmosphere around the south pole. The low pressure area is often cold enough for carbon dioxide snow and frost and the high one has only frost.
So in the winter, there is frost all around the pole and when summer comes, most of the reflective snow stays and the frost sublimates due to its crystals having a large area for absorbing sunlight. Then that leaves the snow in the low pressure zone and bare ground in the high one.
Here's more about the Martian ice caps. Mars, polar caps
very interesting!