Scientists have long known that Mars polar regions are loaded in ice and that the north was mostly water ice. The south pole was thought to be mostly carbon dioxide ice, or dry ice, until NASA observations in recent years showed it to contain some water ice, too.

The orbiter's OMEGA instrument measured the amounts of sunlight and heat reflected from the south polar region.

The results showed that hundreds of square kilometres of ‘permafrost’ surround the south pole. Permafrost is water ice, mixed into the soil of Mars, and frozen to the hardness of solid rock by the low Martian temperatures. This is the reason why water ice has been hard to detect -- because the soil with which it is mixed cannot reflect light easily and so it appears dark.

However, OMEGA looked at the surface with infrared eyes and, being sensitive to heat, clearly picked up the signature of water ice. The discovery hints that perhaps there are much larger quantities of water ice all over Mars than previously thought.

Using this data, planetary scientists now know that the south polar region of Mars can be split into three separate parts. Part one is the bright polar cap itself, a mixture of 85 percent highly reflective carbon dioxide ice and 15 percent water ice.

This new map of the Mars south pole, as derived from OMEGA infrared spectral images, showing the bright polar cap, rich in carbon dioxide (light pink), surrounded by water-rich ice, free of carbon dioxide (green to blue).

Credits: ESA-OMEGA