Take your students beyond memorization to help them understand the inner and outer planets by comparing the characteristics of planets. First, students compare a planet's distance and period of revolution to understand the relationship between distance and number of days or years it takes for a planet to orbit around the sun. Next, students compare the diameter and density of inner and outer planets to explain why the relationship between mass and volume. Last, students describe the planet's surface gravity and weight to understand the relationship between the amount of mass and gravity. This lesson also includes a detailed answer key for your reference.