Ice and sand stripes at the north pole of Mars reveal an ancient climate that fluctuated between warm and cold.
The now dry and dusty Mars still holds water ice at its poles, pointing out that it used to be an ice planet, on which water flowed freely over the surface.
The Shallow Radar (SHARAD) of the Mars Reconnaissance Orbiter has looked deep into the northern ice cap and found buried layers of ice and sand beneath it. The find adds a nuance to the planet's climate history and shows why part of the planet's water remains trapped in the ice rather than being lost in space.
Under the Ice
In the North Pole region of Mars is a place called Cavi Unit, consisting of ice and sand, buried beneath the more visible northern ice cap. SHARAD can look up to one and a half miles into the ice and map the different layers. What it saw were alternating layers of sand and ice.
Researchers know that Mars, like Earth, wiggles its orbit for tens of thousands of years. And while it is shaking and approaching or moving away from the sun, the climate is also "shaking" and becoming warmer and cooler. The researchers believe that the ice was deposited in the Cavi unit during the colder ice ages on Mars. Previously, planetary scientists had assumed that the ice would melt during the warmer periods of Mars. But SHARAD revealed that instead, the ice was covered with sand, which isolated it from the warm rays of the sun. This prevented it from melting or completely lost, as much of the surface water of Mars as its atmosphere diluted.