Martian ice swaps poles every 25,000 years

[Rick]

Water-ice on Mars swaps poles over a cycle that spans 51,000 years or so, in step with the way the planet precesses, or wobbles around on its axis.

Researchers investigating the different types of ice at the Martian poles plugged new data from the Mars Express mission into a model of the planet's climate. Then, adding in details of the planet's slow precession, they ran the clock back 21,500 years to a time when the northern summer was closest to the sun, the exact opposite of the situation today.

More: http://www.theregister.co.uk/2007/07/13/mars_ice_poles/