Enlarge / Mars' northern ice cap. (credit: ESA/DLR/FU-Berlin)
Earth has a climatic pacemaker driven by subtle patterns in its orbit. The shape of its orbit shifts slightly, the tilt of its axis bobs up and down, and that axis wobbles like a top. Add up the way all that movement affects the distribution of sunlight in the high latitude Northern Hemisphere, and you get a predictable succession of glacial and interglacial periods.
Mars has orbital patterns that affect its climate, too. In fact, Mars’ orbital cycles swing to greater extremes than Earth’s. For example, Mars’ current axial tilt is about 25°, but it has varied within a range of 18° to 48° over the past 10 million years. Those orbital changes have influenced its climate as well.
On Earth, the “ice ages” resulted in a transfer of water from the ocean into growing continental ice sheets. On Mars, the changes cause transfers of water ice from the polar caps to lower latitudes, where it forms thin layers and possibly even glaciers. When conditions tilt back the other way, ice disappears from lower latitudes and the polar caps thicken again.
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