The numbers
- How much ice there is
- 1,200,000cubic miles(5,000,000 km³)Enough to cover the whole planet with water over a hundred feet deep
- Where it is
- Mostly in the frozen ground of the poles
- Long ago
- Maybe an ocean over a third of the planet
How it happens, step by step
A wet world
More than three and a half billion years ago Mars had thick air, water that flowed for a long time and maybe an ocean.
The field switches off
The magnetic field made inside the planet stops working, and nothing protects the atmosphere anymore.
The air flies off
The wind blowing from the Sun strips the air away with nothing in its path, for hundreds of millions of years.
The water gives up
With the pressure collapsed, liquid water can no longer last on the surface: it evaporates as soon as it comes out, or it freezes.
The ice hides
What is left retreats to the poles and into the frozen ground, where it still is today, buried and invisible.
To get an idea
Long ago an ocean covered about a third of Mars, in the plains of its northern half.
Mars lost its air because its magnetic field switched off: the Earth still has one, and has kept its air.
Fun facts
These are not in the book: there was no room on paper.
At the south pole, under the water ice, there is also a cap of frozen carbon dioxide.
In 2018 radar found what look like lakes of liquid water under the ice.
Water vapor in the air of Mars was proven in 1963, from a telescope on Earth.
In 2008 and in 2013 two probes found ice by analyzing the Martian soil.
The carved valleys say that water flowed for a long time, not that there were only sudden floods.
When the planet's inner magnetic field switched off, the solar wind was able to strip away the atmosphere.
Test yourself
The first question is the one printed under the QR code, with the answer the book did not give. The other four only exist here.
Question 1 of 5★ is the one from your book
Why can't liquid water stay on the surface of Mars?
Question 2 of 5
How much frozen water has been found on Mars?
Question 3 of 5
What was on Mars more than three billion years ago?
Question 4 of 5
Why did Mars lose its atmosphere?
Question 5 of 5
Where is almost all of the water on Mars today?
Riddles
Once I covered a third of a red world and carved very long valleys. Then the air that held me flew away, and I had to hide underground and freeze. What am I?
There is enough of me out there to cover a whole planet up to the height of a building, and yet almost nobody can see me: I lie buried under the dust and inside the poles. What am I?
People have been looking for me for more than sixty years, first with telescopes and then by digging the soil. Under the ice at one of the two ends, maybe, I have even stayed liquid. What am I?
Try it yourself
Watch the same detail a few months apart: the white patch changes size, because a season has passed on Mars.
Put a teaspoon of water on a hot plate and watch it disappear without flowing. On Mars the same happens, but because the air is missing.
The words
- solar wind
- The flow of particles the Sun blows into space all the time.
Sources: Wikidata (Q1985733), Wikipedia (Water on Mars) and NASA.