Mars’s polar ice caps are made up of Dry ice (CO2) because the atmosphere is
made of 95% CO2.
THEMIS found water by measuring temperatures at the edge of the south
polar cap along a swath 32 kilometers (20 miles) wide. The left image is
THEMIS' daytime infrared view (image I00910002); the same image, colorcoded by temperature, is on the right. Green indicates water ice (I), S is dry
soil, C is CO2 ice, and D is a warm, dark, dusty layered unit cutting into the
polar cap. Areas 1 and 2 were regions studied for seasonal changes.
http://themis.asu.edu/node/5392
Both poles have small permanent (or residual) caps and seasonal (or transient) caps that grow very large then shrink. The
North Pole permanent cap is water ice. The South Pole permanent cap seems to be a mixture of water and carbon dioxide ice.
Both seasonal caps are carbon dioxide ice. The south polar area contains a series of layered deposits thought to be composed
of ice and dust that settled out of the atmosphere. It is composed mainly of frozen carbon dioxide (dry ice) with some water ice
recently discovered. The north polar cap is believed to be composed mainly of water ice and is surrounded by sand dunes.
When the cap recedes during the north polar summer, the residual (remaining) cap is water ice. The seasonal (or transient) cap
that grows in the winter is frozen carbon dioxide.
http://www.isset.org/nasa/tss/aerospacescholars.org/scholars/earthmars/unit2/the_geology_of_mars_icecaps.htm
When searching for life, most astrobiologists agree that water is key. All forms of terrestrial life require water, and while it is
possible that life could evolve without the precious liquid, it is easier to search for conditions that are known to be optimal,
rather than conditions we suppose could be. http://www.space.com/17135-life-on-mars.html
A few million years ago, Mars had a different tilt. The poles were pointing more closely toward the Sun, so the polar ice caps
released massive amounts of water vapor into the atmosphere. Wind carried the vapor south, up and over the slopes of the
Tharsis Montes volcanoes and Olympus Mons, the solar system's largest volcano. The vapor cooled, condensed and fell as
snow. The snow turned to ice over time and formed glaciers. Glacial deposits near the equator on Mars are remnants of snow
on the red planet long ago, scientists said today. Spacecraft observations in recent years have revealed ice-rich landforms and
other clues, including boulders strewn about, that appear to have been caused by glaciers as recently as 350,000 years to 4
million years ago. http://www.space.com/1966-snow-mars-created-glaciers-equator.html
The glaciers, estimated to contain at least as much water as Lake Huron and possibly as much as the entire Great Lakes, were
found by ground-penetrating radar on NASA’s Mars Reconnaissance Orbiter spacecraft. “We have found a big chunk of the
missing water that people have known must be there,” said Ali Safaeinili, a member of the radar team at the Jet Propulsion
Laboratory in La Canada Flintridge, Calif. Scientists analyzing Martian topography have seen lots of evidence of water-caused
erosion on the planet, but until now the only deposits of ice have been seen at the poles. One of the glaciers has been
estimated as being the size of Los Angeles and as much as half a mile thick.
http://www.journalgazette.net/apps/pbcs.dll/article?AID=/20081122/NEWS03/811220333/-1/NEWS09