Complex sentence: It was suspected that a large quantity of frozen water may exist under a thin layer of dust at the south pole and if that were true, then why does it differ from the Martian north pole, a region suspected to contain much less frozen water.
Split into simpler sentences: It was suspected that a large quantity of frozen water may exist under a thin layer of dust at the south pole. If that were true, then why does it differ from the Martian north pole, a region suspected to contain much less frozen water.