Photo credit: ESA/NASA
This image was taken by Tim Peake from the ISS. It shows how thin Earth’s precious atmosphere is.

A planet’s atmosphere determines much of what happens on its surface. Among many other things, Earth’s atmosphere protects us from much of the sun’s harmful radiation, provides us with oxygen to breathe and burns up any space junk or meteorites before they hit Earth. Without our precious atmosphere, life on Earth wouldn’t be possible.

Mars’s atmosphere is about 100 times thinner than Earth’s, which explains why it looks so different from our home planet. But why is it so thin? This clip by NASA explains one theory:

Use Activity 5.4 Protect Your City to plan how you would protect your Mars colony from harmful radiation.