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4.The Inner Planets 2 Mercury VenusEarthMars

3 The four planets that are closest to the sun are called the inner planets Vocabulary Inner planets The four (4) planets closest to the sun: Mercury, Venus, Earth and Mars

4 Mercury is the closest planet to the sun It takes Mercury only 88 days to orbit once around the sun.

5 The surface of Mercury has plains, cliffs, and large holes called craters Mercury is also one of the smallest planets in the solar system

6 Venus is the second planet from the sun It takes 225 days for Venus to travel once around the sun

7 Venus is about the same size as Earth The thick clouds around Venus trap the sun’s heat like a greenhouse

8 So the temperature on Venus can be seven (7) times hotter than the hottest day on Earth!

9 Earth is the third planet from the sun It takes Earth about 365 days to orbit the sun once

10 Earth has one moon. Earth has oceans of water

11 Earth is the only planet with living things as we know them

12 Plants and animals need the water and the atmosphere to stay alive Vocabulary: atmosphere A special mixture of gases around Earth

13 Mars is the fourth planet from the sun It takes Mars 687 days to make one orbit around the sun

14 Mars has two moons

15 Mars is often called the Red Planet because it is covered with a layer of red dust

16 Scientists think that much of Mars was once covered by water. Today, there is no liquid water on Mars But the poles are covered with caps that may be made of frozen water