Lesson 1 of 13
A place in the middle
Show on a big screenSit close to a fire, and you feel hot. Sit far away, and you feel cold. For planets, the Sun is the fire.
Water vapour is water as a gas.
Step 1 of 4
- The Sun sends out heat. A planet's distance matters.
- Too close: too hot. Water is vapour.
- Just right: water stays liquid.
- Too far: too cold. Water is ice.
The rule
The habitable zone is the range of distances where water stays liquid.
Earth is at the right distance from the Sun. Water can stay liquid here. Closer, it would boil away. Farther, it would freeze.
An orbit is the path a planet takes around the Sun. Earth's orbit is nearly circular. So its distance from the Sun changes very little in a year.
Watch out!
The closest planet is not the hottest. Venus is hotter than Mercury. Its thick air traps heat.
Slide the planet. See what happens to its water.
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Try the lab to finish this lesson.