On Earth, there once were about 30 million km3 of total ice mass. The average temperature of an ice mass ranges between −20 °C and −30 °C. The core of an ice cap exhibits a constant temperature that ranges between −15 °C and −20 °C
As you will see an ice cap is a glacier, a thick layer of ice and snow, that covers fewer than 50,000 square kilometers (19,000 square miles). Glacial ice covering more than 50,000 square kilometers (19,000 square miles) is called an ice sheet.