Lesson Overview
This lesson explores small bodies of the Solar System â asteroids, comets, and meteoroids. Learners will discover what these objects are, where they are found, how they differ, and why they are scientifically important, including their role in Solar System formation and potential impact risks to Earth.
Lesson Content (In-Depth)
Small Bodies of the Solar System
Asteroids, comets, and meteoroids are collectively known as small Solar System bodies. They are remnants left over from the formation of the planets more than 4.6 billion years ago. Unlike planets, these objects never grew large enough to become spherical worlds.
Studying these bodies allows scientists to examine primitive material that has remained relatively unchanged since the Solar Systemâs early history.
Asteroids
Asteroids are mostly rocky or metallic objects that orbit the Sun. The majority are found in the asteroid belt between Mars and Jupiter, where Jupiterâs strong gravity prevented these objects from forming a planet.
Asteroids vary greatly in size, from a few metres across to hundreds of kilometres wide. Some asteroids have moons, while others are rubble piles loosely held together by gravity.
A special group, called near-Earth asteroids (NEAs), have orbits that bring them close to Earth. These objects are carefully monitored due to their potential impact risk.
Comets
Comets are icy bodies made of frozen gases, rock, and dust. They originate in the cold outer regions of the Solar System, primarily the Kuiper Belt and the Oort Cloud.
When a comet approaches the Sun, heat causes its ice to vaporise, forming:
A glowing coma around the nucleus
One or more tails that point away from the Sun due to solar wind and radiation
Comets are often described as âdirty snowballsâ and provide valuable information about the early Solar Systemâs composition.
Meteoroids, Meteors & Meteorites
A meteoroid is a small fragment of rock or metal moving through space. When a meteoroid enters Earthâs atmosphere, friction causes it to glow, producing a meteor, commonly known as a âshooting starâ.
If part of the object survives atmospheric entry and reaches the ground, it is called a meteorite.
Meteorites provide direct samples of Solar System material and are studied extensively in laboratories on Earth.
Impacts and Planetary History
Impacts from asteroids and comets have played a major role in shaping planets and moons. Impact craters are found across the Solar System and provide clues about surface ages.
On Earth, impacts may have:
Delivered water and organic molecules
Influenced the evolution of life
Caused mass extinction events
Understanding impact risks is an important part of planetary defence.
Why Small Bodies Matter
Small bodies are scientifically important because they:
Preserve ancient Solar System material
Help explain planetary formation
Provide insight into impact hazards
Offer potential targets for future missions and resource use
Space agencies actively track and study these objects to improve both scientific understanding and planetary safety.
Key Terms Introduced
Asteroid
Asteroid belt
Comet
Coma
Meteoroid
Meteor
Meteorite
Near-Earth object (NEO)