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'Aeronomie
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."
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