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Ice on Mars

Heat and matter · level 2, lesson 6 of 6

A question to start

There are no lakes or rivers on Mars today. Is there any water there at all?

The idea

Mars has lots of water, but nearly all of it is ice. There is ice in its polar caps and ice hidden just under the ground near the poles. It is far too cold, and the air far too thin, for water to stay liquid for long.

Mars has a second kind of ice too. In the polar winter it gets so cold that some of the air itself freezes. Mars's air is mostly carbon dioxide, and frozen carbon dioxide is dry ice. Each winter, enough of it freezes onto a polar cap to take away about an eighth of all the air on Mars. In spring it turns back into gas.

Ice Mars Earth
Water ice Polar caps, and under the ground near the poles Polar caps, glaciers, winter snow
Air that freezes in winter 12 to 16% of all the air None
sol 20: ice lumpssol 24: they have gone

In 2008 the lander Phoenix dug a trench in the far north of Mars and found small lumps of ice. Four days later they had gone. They did not melt into a puddle: the ice turned straight into gas. That is called sublimation.

Worked examples

1. The polar caps. Seen from space, Mars's poles are white, like Earth's.

2. Dry ice. On Earth, dry ice is used to keep things very cold. On Mars it forms by itself in the polar winter.

3. Phoenix's ice. It vanished in four days, without melting, because Mars's air is so thin.

Try it

  1. Where is most of the water on Mars?
  2. What is dry ice?
  3. What happened to the ice lumps that Phoenix found?
  4. Can you find liquid water in lakes on Mars today?
Answers
  1. Frozen as ice, in the polar caps and under the ground.
  2. Frozen carbon dioxide.
  3. They turned straight from ice into gas: sublimation.
  4. No. It is too cold and the air is too thin.

Common mistake

"All ice is frozen water." On Mars, a lot of the winter ice is frozen carbon dioxide from the air.

Where it leads