The picture on the left, taken in mid-September, shows a salmon-coloured notch in the white north polar cap: a storm 600 miles long. The bright dust can also be seen over the dark surface surrounding the cap, where it is caught up in the Martian jet stream and blown east.
The picture on the right, taken in mid-October, shows that the storm has dissipated, though a comma-shaped cloud of dust can be seen curving across the ice cap. The shape is similar to cold fronts on Earth, associated with low-pressure systems. But nothing quite like this has been seen on Mars before.
Scientists have thought that life is more likely to be found near the polar regions, which though cooler, have abundant water.
The polar storm is probably caused by large temperature differences between the polar ice and the dark regions to the south, heated by the springtime sun. The sun also makes the frozen carbon dioxide in the polar cap evaporate. In the second picture, the cap's edge has receded by about 120 miles.Reuse content