Earth's place in the solar system and some internal activities.

1. Earth Inside and Out

3. Here’s what the planet’s orbits look like:

4. Here are the sizes of the planets relative to each other. Did you know that Jupiter has 318 times the mass of Earth and 1,400 times the volume? Or that Jupiter acts as an asteroid catcher?

5. Here are the sizes of the inner four terrestrial (rocky) planets relative to each other. Mercury Venus Earth Mars

6. And here are the sizes of the planets relative to the Sun. The Sun is big. That’s you.

7. We nearly went to 12 planets. The folks who decide what characteristics define a planet (the International Astronomical Union) once proposed that a planet be an object that orbits the Sun (but is not itself a star) and possesses enough gravity to pull itself into a roughly spherical shape. That meant these three could have been planets:

8. It’s possible this definition could have also qualified another 12 celestial objects as planets: Those elementary school styrofoam models of the solar system could have gotten a lot more complicated.

13. Volcanoes form when magma (molten rock) erupts through the crust from the mantle. We’ll talk about them more in 2.3.