On Earth, glaciers covered wide swaths of the planet during the last Ice Age, which reached its peak about 20,000 years ago, before receding to the poles and leaving behind the rocks they pushed behind. On Mars, however, the glaciers never left, remaining frozen on the Red Planet’s cold surface for more than 300 million years, covered in debris. “All the rocks and sand carried on that ice have remained on the surface,” says Levy. “It’s like putting the ice in a cooler under all those sediments.”
Geologists, however, haven’t been able to tell whether all of those glaciers formed during one massive Martian Ice Age, or in multiple separate events over millions of years. Since ice ages result from a shift in the tilt of a planet’s axis (known as obliquity), answering that question could tell scientists how Mars’ orbit and climate have changed over time — as well as what kind of rocks, gases, or even microbes might be trapped inside the ice.
“There are really good models for Mars’ orbital parameters for the last 20 million years,” says Levy. “After that the models tend to get chaotic.”
Image: This image of a glacier on Mars shows the abundance of boulders within the ice. High-resolution imaging of the surface of Mars suggests that debris-covered glacier deposits formed during multiple punctuated episodes of ice accumulation over long timescales. Debris-covered glacial landforms called lobate debris aprons (LDA) are widespread on Mars. It has not been clear whether these LDAs formed over the past 300-800 million years during a single long deposition period or during multiple short-lived episodes of ice accumulation. To address this question, Joseph Levy and colleagues used high-resolution imaging to map boulders along 45 LDAs on the surface of Mars. The boulders are commonly clustered into bands across all LDAs, similar to boulders on ancient terrestrial debris-covered glaciers. The findings point to multiple cycles of ice accumulation and advance over the past 300-800 million years, extending evidence for climate change on Mars beyond the 20-million-year window provided by numerical modeling. (Credit: Joe Levy/Colgate University)
