Mars Once Shuffled Its Icy Poles
Pockets of water ice on the southern pole of Mars, such as these, have been stopped from their once-routine migration by a cap of dry ice, or frozen carbon dioxide. Planetary scientists think the migrations was fueled by an eccentric wobble in Mars'tilt.
Credit: ESA

Mars, as it turns out, once had a propensity for juggling its polar ice caps from one end of the planet to the other.

A perennial wobble in Mars? tilt pushed one pole closer to the sun, causing water ice to evaporate and refreeze at the colder pole, new research shows. Every 51,000 Martian years, the wobble would bring the colder pole closer to the sun again and shuffle the ice cap back to the opposite pole.

?It was a very slow cycle,? said planetary scientist Franck Montmessin of the Service d'A?ronomie in France. ?But something stopped the cycle, and we don?t know what it was. This is another great mystery for Mars? polar ice caps.?

Frosty beverage effect

Montmessin explained that drastic temperature differences at each pole helped drive the cycle.

As the sun evaporated water ice from the warmer pole, the vapors eventually made their way to the opposite pole. Once the water reached the chilly terrain pointed away from the sun, it refroze.

The process is similar to what happens to humid air when it?s introduced to an ice-cold beverage glass--water vapor condenses on the surface and turns to ice.

In this way, millimeter-thin layer by layer, Mars? water ice cap slowly migrated to the cooler pole. But the research team thinks the curious cycle no longer occurs.

Montmessin and his team combined Mars Express orbiter data with advanced computer models of the Martian climate to produce the findings, which will be detailed in an upcoming issue of the Journal of Geophysical Research-Planets.

Ice-capped ice

So far, the research team?s best explanation for the multi-millennia-long cycle's end is that a thick slab of dry ice, or frozen carbon dioxide, capped the water ice in Mars? southern pole.

Montemessin thinks understanding how the cycle?s interruption occurred will yield more of Mars? secrets, including explanations for the forces that fuel global dust storm activity on the planet.

?We?re slowly putting the pieces together and figuring out how the process stopped,? he said. "If we want to understand conditions on Mars that are further in the past, we first need to understand the recent past.?