Final answer:
The largest difference between Mars's northern and southern hemispheres is that the southern hemisphere appears older, with more impact craters, while the southern hemisphere has a polar cap, but none ever forms in the north.
Step-by-step explanation:
The largest difference between Mars's northern and southern hemispheres is that the southern hemisphere appears older, with more impact craters, while the southern hemisphere has a polar cap, but none ever forms in the north.