The document summarizes key facts about the inner planets Mercury, Venus, Earth, and Mars. It describes characteristics of each planet such as diameter, average temperature, composition, distance from the sun, and mass. Mercury is the closest planet to the sun and has an average temperature of 45 degrees. Venus' atmosphere is made up primarily of carbon dioxide and acids. Earth's composition is mostly iron, oxygen, silicon and magnesium. Mars has about 10% of Earth's mass and a thin atmosphere.