CK-12 Foundation
Ck 12: Earth Science: Inner Versus Outer Planets
[Free Registration/Login may be required to access all resource tools.] Compares the characteristics of inner and outer planets.
CK-12 Foundation
Ck 12: Earth Science: Mercury
[Free Registration/Login may be required to access all resource tools.] Recognize the characteristics of the planet Mercury.
CK-12 Foundation
Ck 12: Earth Science: Mercury
[Free Registration/Login may be required to access all resource tools.] Recognize the characteristics of the planet Mercury.
Other
Uppsala Astronomical Observatory: Planetary Imaging
Images of Mercury, Venus, the Moon, Mars, and Jupiter by the Swedish Vacuum Solar Telescope.
Quia
Quia: Brushing Your Teeth
This site gives you opportunities to practice putting the planets in the correct order from the sun. Press "Click here to begin" to get started.