What causes the seasonal change in size of the Martian polar caps? During what season would the largest amount of dry ice be present at the polar cap?

1 Answer
Mar 30, 2016

#CO_2# from the Martian atmosphere condenses upon cooling, then evaporates upon warming. Thus the maximum amount of solid #CO_2# at either pole occurs during that hemisphere's winter.


Mars has a thin atmosphere, but the atmosphere it does have is mostly #CO_2# gas. On Earth this would remain gaseous year-round but Mars is cold enough to allow the #CO_2# to condense during winter, forming "dry ice".

As we see on Earth, winter alternates between hemispheres, and for the same reason. Mars rotates around a tilted axis, which brings alternately more warmth from the Sun to the northern hemisphere and less to the southern hemisphere, then the reverse. The polar #CO_2# ice caps grow and shrink accordingly.

We see the condensation at the poles because the poles are generally colder than the region around the Martian equator. This too is similar to Earth.