Lesson 2: Planetary Formation and Differentiation

How do planetesimals form from material in the protoplanetary disk?

What factors determine whether a planet becomes terrestrial or a gas giant?

How does internal differentiation create layers within planets?

How can observational data from our solar system and exoplanets help us understand planetary formation?

What patterns in composition, density, and distance from the Sun reveal the processes of planetary formation?

Planetesimal

Accretion

Protoplanet

Terrestrial planet

Gas giant

Ice giant

Differentiation

Core, mantle, crust

Volatiles

Density

HS-ESS1-2 – Use models and observational evidence to explain the formation of planets and their internal structures.

NGSS Crosscutting Concepts

Cause and Effect

Systems and System Models

Patterns

Energy and Matter

Students will interpret planetary density, composition, and orbital data to construct evidence-based explanations.

Students will analyze graphs and models showing differentiation and planetary layering.

Students will develop analytical skills by comparing terrestrial and gas giant planets within our solar system.

Students will explore how planets form from small planetesimals in the protoplanetary disk. They will examine how collisions and accretion grow protoplanets and how internal heating leads to differentiation, creating cores, mantles, and crusts. Students will compare terrestrial planets and gas giants to understand compositional differences and patterns in the solar system.

Activities may include:

Modeling accretion using classroom materials (e.g., beads or balls) to form “planets”

Comparing density and composition data for terrestrial and gas giant planets

Creating diagrams showing the internal layers of planets

Purpose: Reinforce understanding of cause-and-effect relationships in planetary formation and differentiation, connecting observations to theoretical models.
DOK Level: 3 – Strategic Thinking / Reasoning (analyzing data and constructing evidence-based explanations)

Connects to missions studying planetary composition, such as NASA’s Juno, Cassini, and Mars rovers.

Helps students understand why Earth has a layered structure and a magnetic field, which relates to habitability and resources.

Provides context for exoplanet research and how other planetary systems may differ from ours.

Students may think planets form instantly rather than gradually through accretion.

Students may believe all planets have the same internal structure regardless of type.

Students may confuse terrestrial and gas giant planets or assume size is the only difference.

Students may not connect differentiation with heat and collisions in early planetary history.

Scaffolded instruction for interpreting planetary composition and density data.

Graphic organizers to track formation stages and internal layers of planets.

Technology integration: simulations showing planetesimal accretion and differentiation.

Peer collaboration for analyzing data and comparing planet types.

Step-by-step guidance for connecting observational evidence to planetary models.

Support for visualizing and interpreting both numerical and conceptual data.

• Checkpoints during modeling exercises and data analysis activities.

• Quizzes on key vocabulary and planetary formation concepts.

• Evaluation of student-created diagrams showing internal differentiation of planets.

• Constructed-response assignments explaining how observational evidence supports the formation and structure of different planet types.

• Astronomy slides and worksheets on planetary formation and differentiation

• Data tables of planetary mass, radius, density, and composition

• Classroom materials for accretion modeling (beads, clay, or balls)

• Simulations showing planetesimal accretion and internal differentiation

• Case studies or articles on planetary structure and comparative planetology