Question Sheet: The trouble with Pluto


Before reading:

  1. How would you describe a planet, so it wouldn’t be confused with other

    objects in space?

  2. Name all the planets that you know.
  3. What is a solar system?
  4. Are there planets beyond Pluto?

During reading:

  1. Why aren’t scientists certain how many planets are in our solar system?
  2. Who came up with the term planet, and what did that term initially mean?
  3. Is the moon a planet? Why?
  4. Who first discovered that the sun, not Earth, is at the center of our solar


  5. What’s the difference between a planet and a plutoid?

After Reading:

  1. Does it matter what we call the objects in our solar system? Why?
  2. Long ago, astronomers thought Earth was at the center of our solar system.

    In the early 1500s, a famous astronomer changed that view, which angered both

    the public and religious leaders. Explain why the idea of the sun being at the

    center of our solar system might be so upsetting to people.

  3. What do you think that Guy Consolmagno meant when he said that it being

    something other than a “planet” turned Pluto from an ugly duckling into a swan?

    Do you agree with him?


  1. People used to think that the sun revolved around the Earth. We now know the

    opposite is true: Earth orbits the sun. That change in understanding Earth’s

    role created what has been called the Copernican Revolution. Why do you think

    changing our view of Earth’s role should have made it easier for people to

    understand and believe later controversial beliefs?

  2. People used to view the nighttime sky and see people, animals and other

    real-life things (the Big Dipper, for example) in the placement of stars and

    planets. Do you think people thought those constellation figures were real or

    just mythical? Why do you think it was important to make up stories for those

    patterns in the sky? How did different parts of the world differ in the images

    they saw in the same groups of stars?

  3. Today, people who live in large cities have a hard time seeing many stars on

    a clear night. Why?

  4. How has the development of powerful telescopes changed how we view the role

    of people in the universe?

  5. Why do some scientists believe intelligent life must exist elsewhere in the

    universe? Do you find their arguments believable?


  1. Pluto is just a dark, cold rock a long way from our sun. Write three

    paragraphs about why you think people care so much about whether it should be

    called a planet or not.

  2. Write a small poem about Pluto.
  3. Hold a classroom debate on why Pluto should — or should not — be called a

    planet. Have one group argue persuasively why it should be included as a planet.

    Let the other group argue why the old label no longer fits with current

    knowledge about the solar system.