Group Size: up to 32 students

45-60 minutes


As the materials around the sun orbited and accreted there was a separation of materials that we can easily see today. The inner planets are denser, rocky and metal rich, while the outer planets are comprised of gases and ice (ice formed from many elements/compounds only found as gases on Earth such as methane and carbon dioxide).

This process did not happen over night; through isotope dating scientists have concluded the approximate age of the solar system to be approximately 4.5 billion years old, the planets forming within this same time frame. (Note: not covered in this unit is the formation of the universe, which is considered to be between 13.5 and 14 billion years old. )

This lesson plans also gives opportunity to reflect on density. Density is a physical property of matter, as each element and compound has a unique density associated with it. Density defined in a qualitative manner as the measure of the relative "heaviness” of objects with a constant volume. “Heaviness” and weight references should be avoided in explaining density as density refers to how tightly packed the molecules of a material are at a specific volume whereas weight incorporates the pull of gravity on the said object.

Learning Objectives:

  1. The inner planets are made of rocky and dense materials; the outer planets are made of gases and ice. The relative densities of the materials that make up certain planets play a role (there are more factors including material volatility) in where they are located.
  2. Separation of the materials and the formation of the solar system occurred about 4.5 million years ago.


Guiding Questions:

What are the materials that make up the inner planets and outer planets? Which planets are made of materials that are very dense? Which planets are made of materials that are less dense? Where are these planets and why are they located where they are located? How long did it take?


Marker per group

Large marble per group

Ball of Styrofoam (same size as marble) per group


4 4-8’ ramps (butcher paper secured can easily substitute) at a 30? angle to floor

4 Wiffle Balls

4 Baseballs

4 Golf Balls

4 Ball of Yarns

4 Balloons

Activity 1: Growing the L.I.N.K.

Direct students to add to their concept maps with information that was covered in the last class; ask students to also add information about what the inner and outer planets are made out of if this has not already been brought up on the concept maps. 3-minutes.

Following the 3-minute activity ask students to look around at other groups concept maps and inquire about vocabulary or concepts they may be unfamiliar. Maps may either be taken down and students prompted to write down what they may have just learned about the topic discussed or maps may be left up for duration of unit to be built upon at a later time in substitution for a word wall.

Class Discussion about the materials of the inner and outer planets and the density and size of the planets.

Activity 2: Exploring Density

In this activity students will be comparing two items of the same volume but different densities. Ask the students to hold the marble in one hand and the styrofoam in the other and compare them, after each student does this have them discuss it with their partner. Density can be a difficult concept to grasp for some students so when I begin discussing it I start with a scenario such as:

“Suppose I put on a blindfold and decided to run around the playground. What is the chances I will run into something? Now, what if I did the same thing but in a thick patch of woods? Why are my chances of hitting a tree greater than the monkey bars?”

Students will talk about weight, mention that weight is relative to gravity, i.e. you weigh 50 kilo on Earth do you weigh more or less on the moon? More or less on Jupiter? Guide them with questions like: How are the materials different, is one thicker than the other? Would one float easier than the other? Why is this so?

Activity 3: Rolling Planets

Have each group set up a ramp of some sort of a minimum length of 4’ at an angle of 30?to the floor. Have each group discuss which one they think gravity will pull down the slope fastest, have the group put them in an order before moving on to the experiment.

Each group should first allow each type of ball to roll down the slope one at a time. They should adjust their predictions and continue with paired testing until they have determined the final order. This activity shows the affects of gravity on weight while giving representations showing different densities for the planets.

The gravitational pull of the Sun helps to pull denser material closer while volatile elements which make up the outer gaseous planets are not easily trapped. Gaseous materials also remain on the outer planets due to temperatures.

Conclusion and Wrap Up:

Discuss each group’s results as a class.

Have the students write down a reflection on how density and the gravitational pull of the sun may affect where different types of planets, gaseous or rocky, may be found in the solar system.

Have students add new concepts to their LINK.

New York State Scope and Sequence:

Intermediate and High School Science Standards

Physical Setting:

Key Idea 1.1a - 1.1c, 1.1e, 1.2 a - 1.2d

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