2. The Inner Planets  The inner planets are the 4 planets closest to the sun:  Mercury  Venus  Earth  Mars  The four inner planets are small and dense and have rocky surfaces.

3. Mercury  Mercury is the smallest terrestrial planet and the planet closest to the sun.  Mercury’s diameter is about 3,000 miles.  Mercury’s distance from the sun is about 36 million miles.  Mercury’s revolution around the sun takes about 88 days.  Mercury’s rotation on its axis takes about 59 days.

4. Mercury  Mercury has flat plains and craters on its surface.  Mercury has no atmosphere.  Mercury is a planet of extremes, with greater temperature ranges than any other planet in the solar system.

5. Mercury  It is so close to the sun that during the day, the side facing the sun reaches temperatures of 806 degrees F.  At night, because Mercury has no atmosphere it drops to as low as -274 degrees F.  Mercury has no moons or rings.

6. Venus  Venus is similar in size and mass to Earth. It is sometimes called Earth’s twin.  Venus’s diameter is about 7,500 miles.  Venus’s distance from the sun is about 67 million miles.  Venus is covered with rock and has many volcanoes, plains, and lava flows.  Revolution around the sun: 7 Earth months (about 210 days).  Rotation: 243 days  It rotates so slowly, its day is longer than its year!

7. Venus  Venus rotates east to west, the opposite direction of most other planets.  Venus’s atmosphere is so thick that it is always cloudy there.  From Earth, astronomers can view a large cloud.  The clouds are made up mostly of droplets of sulfuric acid.

8. Venus  If you could stand on Venus’s surface, you would quickly be crushed by the weight of its atmosphere.  The atmosphere is 90 times greater than the Earth’s atmosphere.  You could not breathe on Venus because its atmosphere is mostly carbon dioxide.

9. Venus  Many probes have visited Venus to gather information. The first probe landed on Venus in 1970.  Venus has no moons or rings.

10. Earth  Earth is the only planet to have liquid water at its surface.  70% of Earth’s surface is by water.  Earth has a suitable temperature range to have water as a solid, liquid, and gas.  Earth has enough gravity to hold on to the gases. These gases make up Earth’s atmosphere.

11. Earth  Earth has an atmosphere that is rich in oxygen.  The Earth’s atmosphere is about 21% oxygen and 78% nitrogen.  Earth’s revolution around the sun takes about 365 ¼ days.  Earth’s rotation on its axis takes about 24 hours.

12. Earth  Earth is about 94 million miles away from the sun.  Earth’s diameter is about 8,000 miles.  Earth has 1 moon and no rings.

13. Mars  Mars is called the red planet.  Mars has a reddish color due to the iron –rich rocks that cover most of its surface.  Mars has an atmosphere that is 95% carbon dioxide.

14. Mars  We can view Mars from Earth with a telescope because it has a thin atmosphere with a few clouds.  Temperatures on Mars range from -220 F to 20 degrees F.  The revolution of Mars around the sun takes about 687 days.

15. Mars  The rotation of Mars on its axis takes about 24 hours and 39 minutes.  The diameter of Mars is about 4,221 miles.  Mars is approximately 141 million miles from the sun.  Some regions of Mars has volcanoes. Mars contains the largest inactive volcano in the solar system: Olympus Mons.

16. Mars  Scientists believe the a large amount of water once flowed on Mars.  At present, liquid water cannot exist on Mars because its thin atmosphere would cause evaporation to occur.  The water that once existed is now frozen in polar ice caps with carbon dioxide and small amounts of water vapor.

17. Mars has a tilted axis similar to the Earth; therefore, scientists believe it has seasons similar to Earth. Mars has 2 moons and no rings.