| A | B |
|---|
| Mercury | shortest revolution, closest to the sun, many craters on rocky surface |
| Inner planets | Mercury, Venus, Earth, and Mars |
| No moon | Venus |
| rotation | the spinning of a sphere on its axis; causes day and night |
| Venus | hottest planet, thick clouds hold in heat; acid droplets in clouds |
| Earth | the only planet with water and life |
| Mars | reddish soil, fourth from the sun, has seasons |
| Moons of Mars | Two moons - Phobos and Deimos |
| Astronomical Unit (A.U.) | the distance of the Earth from the sun. Earth's AU = 1 |
| Inner planets | Mercury, Venus, Earth, and Mars |
| Meteorite | a meteor that did not burn up all of the way in Earth's atmoshpere and hits the Earth |
| orbit | the path taken by a smaller object as it revolves around a larger one |
| Earth year | 365 days |
| Mercury's year | 88 days |
| Has a year longer than an earth year | Mars |
