It’s been about 12,000 years since Earth’s glaciers last retreated, having finished carving out the Great Lakes, depositing boulders in strange places, and generally giving the northern hemisphere a makeover. But that does not mean Earth’s most recent ice age is over. We are currently in an interglacial, a warmer period sits between the longer glacial periods of an ice age, which itself lasts a few million years.
Mars has ice ages, too, but its temperature swings are more extreme. According to scientists, the Red Planet is emerging from an ice age of its own, following several rounds of climate change. Radar evidence says this retreat began about 370,000 years ago.
Understanding this history gives scientists a window into Mars’ deeper past, helping them understand when the planet’s climate might have been friendly to life. But the story of Mars is also a fable for Earth. Understanding the Martian climate, and what causes its ice ages, can help us learn more about why they happen here—at a time when the intricacies of Earth’s climate are of great concern.
Isaac Smith has been looking at Texas-sized curlicues in the Martian ice caps for eight years, trying to connect them to the planet’s climate history. Smith, a postdoctoral researcher at the Southwest Research Institute in Boulder, Colo., used the Mars Reconnaissance Orbiter’s shallow radar instrument to peek beneath the ice cap on Mars’ north pole. He studied two-dimensional radar slices, which enabled him to see the ice in cross-section, like looking at a road cut or a layer cake. He found something that surprised him: The polar ice cap is active. Ice is constantly piling up and eroding, not just in one spot but everywhere.