The Goldilocks Principle: A Model of Atmospheric Gases

In class discussions, you've become familiar with the differences between the atmospheres of Venus, Earth, and Mars, and why they seem to follow what atmospheric scientists call The Goldilocks Principle: "Venus is too hot, Mars is too cold, but Earth is just right!" This activity will give you more direct experience with the simulated atmospheres of all three planets.


  1. According to your teacher's directions, work in pairs or teams.

  2. Using the materials provided (it may be jellybeans, colored cotton balls, or dry beans), you will be building samples of the atmospheres of Earth, Mars, and Venus in small re-sealable bags. Your teacher will tell you which materials will stand for which of the gases in the atmosphere. For example, if you are using jellybeans, you may be instructed to let yellow jellybeans stand for nitrogen, blue jellybeans for oxygen, black jellybeans for carbon dioxide, etc.

  3. Each team will fill 3 re-sealable bags to represent the atmospheres of each planet. Each bag will have 100 jellybeans (or cotton balls, or beans, etc.). Your teacher will display a table that tells you what percentage of the different types of gases each atmosphere has. Your job will be to select the correct number and color of jellybeans to place into the bag to show those percentages. For example, if a planet has an atmosphere that is 50% nitrogen, 25% carbon dioxide, and 25% oxygen, you would add 50 yellow beans, 25 blue beans, and 25 black beans to the bag. WARNING: sometimes the amount of a particular gas may be less than 1%, which means that you have to add less than one whole jellybean!

  4. When you are done, you will see that the bags contain very different colored beans, but they all have the same total number of beans. That's not the way it is on the real planets. Venus has an atmosphere 90 times thicker than Earth's and Mars has an atmosphere more than 100 times thinner! If you made a bag with 100 beans to represent Earth's atmosphere, then to show the correct density of the atmosphere, your Venus bag would have 9000 jellybeans, and your Mars bag would have less than 1 jellybean!

Observations and Questions

  1. Look at the other bags made by your classmates. Do they all look the same? Why or why not?

  2. In your journal or on a sheet of paper, answer these questions:
    a. Describe the atmospheric conditions you might encounter as an astronaut setting foot on Venus and Mars (remember density!).
    b. Name at least two ways that the atmospheres of Venus and Mars are similar to each other, and one way that both differ from Earth's.
    c. What new information did you learn in this lesson? What did you already know? What was the hardest thing about the activity?

When you're finished with the activity, click on Back to Teacher Guide at the top of the page.