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SOL 6.8 / Earth/Space Systems Part 3 Page 1 The Solar System: The Planets The planet closest to the sun is Mercury. Not much larger than Earth’s moon, Mercury has a very thin atmosphere and extreme surface temperatures. Daytime highs can reach 425°C while nighttime temperatures plunge to -170°C. Mercury has no moons. The second planet from the sun is Venus. Venus is similar to the Earth in size and has a thick atmosphere of carbon dioxide. It is always cloudy on Venus. Due to the greenhouse effect, Venus is the hottest planet in the solar system with temperatures reaching over 460°C. Like Mercury, Venus has no moons. Earth, is one of the small, rocky planets in our solar system and is the third planet from the sun. Scientific evidence indicates that the Earth is about 4.5 billion years old. It is made up of active layers of rock and is covered by large areas of land called continents and large bodies of liquid water called oceans. Frozen ice caps are located in its polar regions. Earth also has a protective atmosphere composed of predominately nitrogen and oxygen. This atmosphere, along with a natural magnetic field, helps to shield the Earth’s surface from harmful solar radiation. With its oxygen-rich atmosphere and lifesupporting water, scientists believe that Earth is the only planet that is home to living organisms. Earth has one moon. Mars is the fourth planet from the sun and about half the diameter of Earth. Due to its increased distance from the sun and its thin atmosphere, Mars is a very cold planet with temperatures ranging from 37°C to -123°C. Mars has two very small moons. © 2006 SOL 6.8 / Earth/Space Systems Part 3 Page 2 The Solar System: The Planets (continued) Jupiter is the fifth planet from the sun. Jupiter is the largest planet in the solar system and is 300 times more massive than the Earth. Unlike the rocky inner planets, Jupiter is a giant ball of liquid hydrogen and helium with a temperature of -153°C. It is one of the four outer planets called gas giants. Four larger moons and a number of smaller moons orbit it. Saturn is the sixth planet from the sun. Saturn is another gas giant with temperatures plunging below -185°C. It is slightly smaller than Jupiter and is mainly composed of hydrogen and helium. Saturn has 5 large moons, a number of smaller moons, and a huge system of rings encircling it. Saturn’s rings consist of chunks of ice and rock. Uranus is the seventh planet from the sun. It is a gas giant made up mostly of hydrogen and methane. Smaller than the other gas giants, Uranus is only four times the diameter of Earth. It is two times farther from the sun than Saturn and temperatures on Uranus stay around -214°C. It also has five large moons, a number of smaller moons, and ten thin rings. Neptune is the eighth planet from the sun and the last of the gas giants. It is composed of hydrogen, helium, and methane and has a temperature of -225°C. Neptune is a little smaller than Uranus and has more than ten moons in orbit around it. One of Neptune’s moons, Triton, is the largest moon in the solar system. © 2006 SOL 6.8 / Earth/Space Systems Part 3 Page 3 The Solar System: The Planets (continued) The solar system is so vast; it is difficult for us to imagine the great distances between the planets and the sun. In order to visualize very small objects like atoms, or very large objects like our solar system, we need to use models or scaled drawings. A scale is a ratio between two distances. On a road map of your county, town, or city, the ratio or scale might be: 1 centimeter = 5 kilometers. For us to create a scale map of something as large as our solar system, 1 cm will have to equal millions of kilometers. The following chart will help us understand the relative positions of the planets from the sun. Can you use this chart to make a model or scaled drawing of our solar system? Planets Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Pluto Scaled Distance (cm) 2 4 5 8 26 47 95 150 196 © 2006 Actual Distance (km) 58,000,000 108,000,000 150,000,000 228,000,000 778,000,000 1,427,000,000 2,869,000,000 4,505,000,000 5,890,000,000