MEPX
Chapter 3 of 12All chapters
  1. 1The scale of things
  2. 2The Sun
  3. 3The rocky planets
  4. 4The giant planets
  5. 5Moons
  6. 6Asteroids and comets
  7. 7Gravity and orbits
  8. 8Light and distance
  9. 9Stars and their lives
  10. 10Galaxies
  11. 11The expanding universe
  12. 12Observing for yourself

Chapter 3 of 12

The rocky planets

Mercury, Venus, Earth and Mars.

The inner four

Outward from the Sun: Mercury, Venus, Earth and Mars. They are small, dense and made of rock and metal, because the young Sun blew the lighter gases outwards.

  • Mercury is closest, but Venus is hotter because its thick atmosphere traps heat.
  • Mars is half the width of Earth and holds the tallest volcano in the solar system.

Atmospheres

Mercury has almost none, Venus has a crushing carbon dioxide blanket, Earth has nitrogen and oxygen, and Mars has a thin remnant. Mass and distance from the Sun decide what a planet can hold on to.