2. The Inner Planets The four planets closest to the Sun:
Mercury, Venus, Earth, and Mars
Also called the “terrestrial planets”
Smaller than the outer planets
Solid, rocky surfaces
Separated from the outer planets by an asteroid belt

3. Mercury Moons: 0 Rings: 0 Closest planet to the Sun Very small planet
Made of rock and methane ice
Almost no atmosphere
Variable temperature; nights are colder than our coldest nights on Earth, days are hotter than our hottest days
Solid surface is covered with craters
Only takes 88 days to orbit the Sun

4. Venus Moons: 0 Rings: 0 About the same size as Earth
Second planet from the Sun
Surface is rocky
The hottest planet and very dry
Atmosphere is mostly made of carbon dioxide
Atmosphere is so thick that we need probes to see its rocky surface
Takes 225 days to orbit the Sun

5. Earth Moons: 1 Rings: 0 Third planet from the Sun
Atmosphere is 77 percent nitrogen and 21 percent oxygen, with some carbon dioxide and water vapor
Liquid water covers most of the surface; the rest is rock and soil
White clouds of water vapor are in the atmosphere
Temperature is moderate
Takes 365 days to orbit the Sun

6. Mars Moons: 2 Rings: 0 Fourth planet from the Sun
Surface had liquid water a long time ago; now, all the water is frozen in polar ice caps.
Thin atmosphere is mostly carbon dioxide
Surface is rocky
Temperature is moderate
Small planet
Nickname: “the red planet” (red soil)
Takes 2 years to travel around the Sun