Unit D: The Earth in Space

On which planet is the largest volcano in our solar system?

1. Get Set to Explore


  • atmosphere: Layer or layers of gases that surround a planet.
  • diameter: The distance from one side of a planet to the other side, passing straight through the middle of the planet.
  • gas giant: One of the four large outer planets that is made mostly of gases.
  • solar system: The Sun, planets, moons, and other space objects that orbit the Sun.
  • volcano: An opening in the crust of a planet through which melted rock, hot ash, and gases escape.

Building Background

  • With the exception of the last word, volcano, review the vocabulary words and their definitions with the class.
  • Refer students to the drawing on Student Edition pages D4ĞD45. Let volunteers name the planets, and write the names on the board. Challenge each student to tell you one fact about one of the planets. List the facts next to the planet's name and leave room to add other information after students have done the simulation.
  • Ask students what a volcano is, and elicit a definition from the class. You might show students a picture, as on Student Edition page C21. Explain that Earth isn't the only planet that has volcanoes. Let students hypothesize about other planets that might have volcanoes. Ask them to give the facts that led them to their hypotheses.
  • Read the Discover! question aloud and let students restate it in their own words. Prompting students to refer to their previous ideas about which planets would have volcanoes, elicit possible answers from the class. Write each answer on the board. Then, hold a class vote on the planet students think has the largest volcano. Tally the votes on the board.

2. Guide the Exploration

  • Have students launch the Discover! Simulation. Call their attention to the pictures of the planets near the bottom of the screen. Students can click a planet to launch a space probe and learn more about the planet.
  • Encourage students to take notes on what they learn about the planets. They should make special note of things they found interesting or surprising.

3. Review/Assess

  • Go over Step 3's Wrap-up text with the class, sentence by sentence. Help students understand the comparison between Mars's largest volcano—Olympus Mons—and one of the largest volcanoes on Earth—Mona Loa. Point out that more than half of Mona Loa is underwater, which is why it isn't considered one of Earth's tallest mountains. Note that the height of mountains is officially measured from sea level.
  • Present the Extension activity. Guide students to realize that they need to use the diameter to make size comparisons. Use a discussion format to share answers.
    • Earth is the only planet with liquid water.
    • The following planets are larger than Earth, in order starting with the largest: Jupiter, Saturn, Uranus, Neptune.
    • The following planets are smaller than Earth, in order starting with the planet closest in size to Earth: Venus, Mars, Mercury, Pluto.

If time permits, present students with the following questions:

  • Inquiry Skill Use Numbers Compare the size of Olympus Mons with that of Mona Loa. How much taller is Olympus Mons than Mona Loa? Answer: For a hint, tell students to multiply the height of Mona Loa by the number that they think they need to get close to the height of Olympus Mons; alternatively students could add the height of Mona Loa the number of times they think is necessary for the sum to be close to the height of Olympus Mons. The answer is Olympus Mons is about 2 1/2 times as large as Mona Loa.
  • Critical Thinking Synthesize Which planet rotates the fastest? How can you tell? Answer: Students need to compare the length of the day on each planet. The planet with the shortest day rotates the fastest. This is Jupiter, with a day that is only 9.8 hours long; it is followed closely by Saturn, whose day is 10.2 hours long.

4. Reaching All Learners

On Level: Kinesthetic Learners

Have students write nine signs, each sign having the name of one of the planets. Hand out the signs to students. Let kinesthetic learners direct the students with the signs to line up in order of the planets of the solar system, starting with the planet closest to the Sun. As an extra activity, students can use different size sheets of paper, writing the name of the largest planet on the largest sheet and of the smallest planet on the smallest sheet. Then students can line up in order from the smallest planet to the largest planet.