What do Mercury, Venus, Earth, and Mars have in common? They are all inner planets. These four planets are closest to the sun. Explore the inner planets with content tied to the curriculum of upper-elementary and middle school students and easy-to-understand text written at a 3rd grade reading level. Dyslexia-friendly font and design make learning accessible, while a recap at the end promotes checking for understanding to aid in comprehension. It's key space science curriculum made approachable for all.