Rings Around a Planet: Saturn’s rings have fascinated sky gazers since the astronomer Galileo first saw them in We’ve learned that the rings are made of rock, gas, and ice. Page 314

Page 316

Page 317 o The inner planets are those closest to the sun; they are Mercury, Venus, Earth, and Mars. These planets are alike in many ways. They all have rocky surfaces and are smaller than most of the outer planets. Also, none of the inner planets has more than two moons. o There are also many differences—Mercury is hot enough to melt lead while Mars never gets above 68°F. o Earth is the most unusual inner planet. Only Earth has liquid water on its surface and a large amount of oxygen in the atmosphere. This water and oxygen help support life on Earth.

Page 318 o Beyond Mars, on the far side of the asteroid belt, are the outer planets. They are Jupiter, Saturn, Uranus, and Neptune. o These 4 planets are huge and made mostly of gases. They are often called the gas giants. o They all have many moons, and they all are surrounded by rings that are made of dust, ice, or rock. o Pluto is no longer considered an outer planet .