10. Asteroids, Comets, and the Origin of the Solar System

Overview

In the last four modules, you explored the planets of our Solar System — their atmospheres, internal structures, magnetic fields, rings, and moons — and how they’ve evolved since their formation. You are now ready to bring that knowledge together and examine the smaller bodies that preserve the Solar System’s earliest history.

Unlike the major planets, which have undergone billions of years of geological change, asteroids and comets remain relatively unaltered. These remnants of the original solar nebula act as time capsules, recording the conditions that prevailed when the Sun and planets were born. By studying their orbits, compositions, and interactions, we can reconstruct how the Solar System formed and evolved.

This module begins with a first look at the nebular hypothesis — the idea that the Sun and planets formed together from a rotating disk of gas and dust. You’ll then explore the asteroid belt and the cometary reservoirs that lie beyond Neptune, comparing how these populations differ in composition and origin. We’ll examine key space missions such as Dawn, Rosetta, OSIRIS-REx (and its extended OSIRIS-APEX mission to Apophis), Hayabusa2, Lucy, and Psyche, which are providing close-up data on primitive bodies and testing models of planetary formation. You’ll also learn how fragments that reach Earth as meteorites reveal the chemistry of the early Solar System.

Finally, you’ll turn back to the question of origins. Using clues from small bodies, isotopic dating, and orbital dynamics, you’ll evaluate the Nice model and related theories of planetary migration — models that explain how the giant planets’ movements shaped the asteroid belt, Kuiper Belt, and ultimately, the conditions that allowed Earth to form.

Learning Objectives

  1. Explain what asteroids, comets, and meteoroids are, and describe where they originate within the Solar System.
  2. Explore scientific results from major space missions that have studied comets and asteroids, and discuss what these missions reveal about Solar System formation.
  3. Distinguish between meteors, meteorites, and meteoroids, and explain how they connect to larger parent bodies.
  4. Describe the nebular hypothesis and evaluate the evidence supporting modern models of Solar System formation and planetary migration.
  5. Synthesize knowledge of individual Solar System components to explain the system’s overall structure and chemical diversity.

Key Terms and Concepts

  • Asteroids / Asteroid belt
  • Comets / Cometary nuclei
  • Nebular hypothesis
  • Planetesimals
  • Protostar / Protoplanetary disk
  • Conservation of angular momentum
  • Pebble accretion
  • Dawn mission
  • Rosetta mission
  • OSIRIS-REx / OSIRIS-APEX mission
  • Hayabusa2 mission
  • Lucy mission
  • Psyche mission
  • Yarkovsky effect
  • Meteoroid / Meteor / Meteorite
  • Nice model
  • Planetary migration
  • Solar System formation