Radar reveals that Mars is hiding past ice caps under the ones visible today. (Credit: SA/DLR/FU Berlin; NASA MGS MOLA Science Team)

Bands of ice and sand at Mars’ north pole reveal an ancient climate that swung between warm and cold.

Mars, now dry and dusty, still holds water ice at its poles, and evidence strongly suggests it was once a planet where water flowed freely across the surface.

The Mars Reconnaissance Orbiter’s Shallow Radar (SHARAD) has peered deep into the northern ice