TEKS identify the planets in Earth s solar system and their position in relation to the Sun Our Solar System The Planets A solar system is made up of a star and everything that revolves around it. Our solar system consists of the sun, eight planets, many moons, many dwarf planets, an asteroid belt, comets, meteors, and other celestial objects. The sun is the center of our solar system. It is by far the largest object in the solar system. The sun makes up more than 99% of the solar system s mass! All other objects that are in the solar system orbit the sun. A planet is a large, spherical body that revolves around a star. The planets, in order from the sun, are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. All of the planets as well as most other celestial bodies orbit the sun in roughly circular orbits that lie in the same plane, which is known as the ecliptic. Inner Planets vs. Outer Planets The inner planets Mercury, Venus, Earth, and Mars are relatively small. They are also made of rock and have few or no moons. The outer planets Jupiter, Saturn, Uranus, and Neptune are huge, mostly gaseous, and have rings. The outer planets also have many moons. In general, the farther a planet is from the sun, the colder it is. Between Mars and Jupiter is the asteroid belt, a ring-shaped area where there are many asteroids. Asteroids are small bodies in space made of rock or metal. There are other areas of asteroids, too, but this is the main belt. Some of the particles are left over from the formation of the solar system. Other bodies have been added as they break off planets or enter our solar system. The Solar System Mercury Earth Jupiter Saturn Uranus Neptune Venus Mars This diagram is not to scale. Also, the planets do not line up in a straight line. They are all at different points in their orbits around the sun. and Assessment TEKS Page 1 of 6
You may know that Pluto was once considered to be the ninth planet in our solar system. It is not very large, and there are other objects in its orbit. Astronomers found other objects similar to Pluto and think there may be many more. Scientists had a decision to make either classify many other objects as planets or modify the definition of a planet. Scientists chose to classify Pluto as a dwarf planet in 2009. Eris, Ceres, Haumea, and Makemake are four other dwarf planets in our solar system. Features of the Planets Mercury, which is closest to the sun, is about the size of Earth s moon. Like the moon, Mercury has almost no atmosphere and a surface covered with craters and dust. The side of Mercury facing the sun is hot about 430 C (810 F)! The side not facing the sun can become very cold, however about 180 C ( 290 F). Venus is the brightest object in the night sky, after the moon. This planet is about the same size as Earth, and it is rocky. The similarities end there. Venus can become very hot, reaching about 460 C (860 F). It is even hotter than Mercury because Venus s thick atmosphere keeps heat from escaping. Earth, the third planet from the sun, is our home. Earth is the only planet on which life is known to exist. About three-fourths of the surface of our planet is covered with oceans of liquid water. This makes Earth unique among the planets and gives our planet the nickname the blue planet. Mars is called the red planet because of its reddish soil. Its atmosphere is mostly carbon dioxide. Scientists have evidence that liquid water once existed on Mars. Mars has the largest volcano in the solar system, and it has dust storms that can last for months. Beyond the asteroid belt are the outer planets. These are also called gas giants because they are composed mainly of hydrogen and helium. Jupiter is the largest planet in the solar system. It has rings and dozens of moons. There is a huge storm on Jupiter that has lasted for more than 400 years. The storm, like a hurricane, has a name the Great Red Spot. Saturn is best known for its rings, made of ice, dust, boulders, and frozen gas. The rings stretch about 136,200 km (84,650 mi) from the center of the planet! Like Jupiter, Saturn has dozens of moons. Uranus also has many moons and rings. This planet rotates on an axis that is tilted much more than those of the other planets. Uranus looks like a top that has fallen over but is still spinning. Neptune has many rings and moons and the fastest winds in the solar system. The winds can reach 2,000 km/hr (1,200 mi/hr)! Number of Known Moons Mercury 0 Jupiter 63 Venus 0 Saturn 62 Earth 1 Uranus 27 Mars 2 Neptune 13 Jupiter has a very faint ring. The diameter of Jupiter is more than 11 times larger than the diameter of Earth! and Assessment TEKS Page 2 of 6
Hands-On Activity A Scale Model of the Solar System Most images of the solar system are not to scale. The sun is so large and the planets are so far apart that it is not easy to show all the elements of the solar system to scale. In this activity, you will make a scale model of the solar system. Materials 4-m length of string tape measure 8 markers of different colors Procedure: 1. At one end of the string, make a knot. This will represent the position of the sun. 2. One AU (astronomical unit) is equal to the distance between Earth and the sun. In your model, 10 cm will represent 1 AU. Use the tape measure to find Earth s position in the model. Use a marker to mark this point on the string. Place a small dot next to the planet s name in the table to record which color you used. 3. Complete the Scale Distance column of the table. Repeat Step 2 for each planet, using a different color marker for each. Planet Data Planet Average Distance from the Sun (km) Average Distance from the Sun (AU) Scale Distance (cm) Planet s Diameter (km) Mercury 58 million 4/10 4 4,879 Venus 108 million 7/10 7 12,104 Earth 150 million 1 12,756 Mars 228 million 1 5/10 6,792 Jupiter 779 million 5 2/10 139,822 Saturn 1,433 million 9 6/10 120,536 Uranus 2,877 million 19 2/10 51,118 Neptune 4,503 million 30 1/10 49,528 Discussion Questions: 1. How would you describe the positions of the planets? 2. How could you add to your model to make it more accurate? and Assessment TEKS Page 3 of 6
Our Solar System Label the solar system diagram. In what ways is the solar system drawing above not to scale? What other objects are part of our solar system? and Assessment TEKS Page 4 of 6
TEKS Assessment Fill in the letter of the best choice. Look at the drawing below. Look at the image below. Which planet is the arrow pointing to? Neptune Saturn Jupiter Earth Which planet has the shortest path around the sun? Earth Mercury Venus Neptune Which of the following planets is closest in size to Jupiter? Saturn Mars Mercury Earth Which planet is farthest from the sun? Saturn Uranus Neptune Jupiter Which of the following is not true? This planet has more moons than Earth. This swirl you can see is a giant storm called the Great Red Spot. This planet is many times larger than Earth. This planet s surface is much like Earth s surface. Why is Pluto no longer considered to be a planet? It does not orbit the sun. It has too many moons. It is not large enough to have cleared its orbit of debris. It is too large to be classified with the inner and outer planets. and Assessment TEKS Page 5 of 6
Answer Key Hands-On Activity (p. 3) 1. Answers will vary but should be based on the models. Sample answer: The four inner planets are close to the sun and relatively close to one another. The four outer planets are spaced farther apart and are much farther from the sun. 2. Check students answers. Sample answer: I could make the size of the planets to scale. Student Response Activity (p. 4) 1. Check students answers. Beginning with the closest to the sun, students should label Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. 2. Neither the distances of the planets from the sun or the relative sizes of the planets are to scale. 3. Dwarf planets, asteroids, comets, dust, gases, and the moons of the planets are also part of the solar system. TEKS Assessment (p. 5) 1. D 2. B 3. A 4. C 5. D 6. C and Assessment TEKS Page 6 of 6