2. THE OUTER PLANETS Jupiter, Saturn, Uranus, and Neptune are the outer planets. They are all large compared to the inner planets. Jupiter has a diameter that is 11 times that of Earth. They all have very small hard cores but are mostly gaseous, therefor they are called the gas giants. They all have such a strong gravitational pull that they have thick atmospheres.

4. We think that each of the outer planets has a small core of solid rock, ice, carbon dioxide or other compounds. JUPITER Jupiter has a thick atmosphere of hydrogen and helium. It has many colorful bands. It also has a giant red spot that is believed to be a storm that has been going on for a long time. Galileo found four moons around Jupiter.

5. There names are Io, Europa, Ganymede, and Callisto. We have found 13 more moons for a total of 17. Jupiter almost became a star. It did not get quite hot enough to fuse. It does give off more energy than it receives from the sun. SATURN Saturn is slightly smaller than Jupiter. It also has a thick atmosphere of hydrogen and helium.

8. Saturn is the only planet that is less dense than water. It is the only planet that would float on water. Saturn’s famous rings are made of chunks of rock and ice that are orbiting the planet. From Earth it looks like a few rings but there really are hundreds of thin rings. Saturn has nineteen moons.

11. URANUS Uranus is much smaller than Jupiter or Saturn. It is twice the distance from the sun as Saturn so it is much colder. Looks blue due to methane gas in its atmosphere. Uranus was the first planet discovered in modern times. Voyager 2 photographed Uranus. It rotates on its side. It has several rings. Uranus has 17 moons.

13. NEPTUNE Neptune is 30 times the Earth’s distance from the sun. Its atmosphere contains visible clouds. Neptune was discovered because Uranus was not following its predicted path. Astronomers predicted that another planet must have an effect on Uranus. Voyager 2 passed Neptune and found colored spots. The Hubble telescope later found the spots to be gone. Neptune has 8 moons.

16. PLUTO AND CHARON Pluto is not a planet. It is more like a comet but it orbits the sun like a planet. It has a moon called Charon.