Education and
Public Engagement
at the Lunar and Planetary Institute
Explore! Mars: Inside and Out

Recipe for a Planet

Overview

Recipe for a Planet is a 45 minute activity in which children ages 8 to 13 build edible models of Earth and Mars to compare their sizes and illustrate their internal layers.

What's the Point?

Materials

For each child:

For each team of 3 to 4 children (or for each individual child if you prefer that they make their own planets):

For the group:

For the Facilitator:

Preparation

You may need to modify this activity for children with dietary restrictions.

Activity

1. Introduce the activity by dividing the children into teams of 3 to 4 and explaining that each team will create edible models of Earth and Mars. Invite them to share what they know about Mars:

2. Before you begin, explain to the children that this is a fun and tasty — but messy — activity! Have them wash their hands before they start and remind them to not lick their fingers while they are working on their models. For now, they will just make the model — they will be invited to eat it at the end of the activity!

3. Create a model of Earth! Provide the materials to the teams and invite them to create a model of Earth.

Earth's inner metallic core: a donut hole
Earth's molten outer core: red icing
Earth's mantle: 3 1/2 Rice Krispies Treats
Earth's oceanic crust: blue sprinkles or "jimmies"
Earth's continental crust: 1/2 of a Rice Krispies treat covered in green sprinkles or "jimmies"

Have each team tear one of their Rice Krispies treats in half and set one half aside. Mash the other half together with 3 more Rice Krispies Treats so they make one "mega treat." Have them form the treat into a flat rectangle, about 4 inches by 6 inches. Starting in the center of the flattened "mega treat," smooth a thin sheet of the red icing to within one inch of each edge; they should use about half of the icing and save the rest for later. Place the donut hole in the middle. Gently wrap the Rice Krispies Treats around the donut hole — with the icing side against the donut hole — to form a ball. Roll it around and squeeze it to make it firm.

Invite the children to add continental and oceanic crusts to their Earth. Have them place their Earth sphere in the baggie with the blue sprinkles. Roll it around until it is thoroughly covered in blue. Remove and set it aside.

Now invite them to make the continental crust — the land on Earth. Ask them to take the Rice Krispies Treat half they set aside earlier and flatten it into a thin layer. Have the children create four or five continent shapes, then gently press one side of each continent into the green sprinkles until covered. Have them gently press each continent onto the Earth sphere with the sprinkle side up. In reality, the thicker continental crust does not "sit" on top of the oceanic crust; both sit above the Earth's mantle.

4. Create a model of Mars. Provide the materials to the teams and invite them to create a model of Mars.

Mars' inner core: 2 tablespoons of red icing
Mars' mantle: 2 Rice Krispies Treats
Mars' crust: red sprinkles

Have the teams shape their Rice Krispies Treats into a rectangle about four inches by two inches. Place the red icing in the center and gently wrap the Rice Krispies Treat around it, shaping it into a ball.

Have the children place their Mars sphere in the baggie with the red sprinkles and roll it around until it is thoroughly covered in red. Remove and set aside.

5. Invite the children to examine and discuss their models.

6. Revisit their crater ideas.

7. Revisit their volcano ideas and their findings from earlier activities.

Invite the teams to add chocolate chip volcanos to their Earth and Mars models, based on their observations and what they learned in other activities. They may want to use the left-over red icing to help the chocolate chips stick.

8. Ask the children what volcanos tell us about a planet.

Planetary scientists hypothesize that some of Mars' volcanos were active not very long ago, between 10 million years ago and a hundred million years ago. They suggest this because the volcanic rock around many of the volcanos is not heavily cratered; the surface appears fresh.

9. Have the children spend a few minutes talking in their groups about what the inside of their Earth and Mars model planets will look like if they cut them open. Invite them to draw their predictions if they wish.

10. Return to their models and have the teams carefully cut both Earth and Mars in half. Small children may need help cutting, and they may need to reshape the planets after cutting.

11. Invite the teams to examine the cross sections of their planets.

  • Earth has a layer of icing that represents the liquid molten outer core. Earth has a solid inner core.
    Share with older children that Earth's molten layer of material — iron and nickel - is very important. Convection (flow) of material in Earth's outer core creates Earth's magnetic field. This magnetic field protects us from dangerous particles from the Sun called solar wind. Without a magnetic field, these particles would wear away our atmosphere and dangerous radiation from the Sun would reach Earth's surface.
  • Mars also has a molten core — but no solid inner core.
    Share with older children that because there is not convection within the liquid core, Mars does not have a magnetic field like Earth's. Without this protective magnetic field, solar wind has worn away the atmosphere of Mars, and dangerous radiation reaches its surface.
  • In general, Earth has two different types of crust — thick crust where there is land (continental crust) and thin crust under the oceans (oceanic crust). On Mars, the crust is relatively thick everywhere.

Conclusion

Ask the children if they think the differences in the interiors of Mars and Earth are somehow related to the differences in their surface features. Give them a few minutes to discuss the possible relationship. You may wish to have them share some of their ideas and record them in their GSI Journals.