Lesson Overview
This lesson explores moons, also known as natural satellites, which orbit planets and dwarf planets throughout the Solar System. Learners will discover the diversity of moons, how they form, and why some moons are among the most promising places to search for life beyond Earth.
Lesson Content
What Are Moons (Natural Satellites)?
Moons are natural objects that orbit planets or dwarf planets due to gravity. Unlike artificial satellites built by humans, natural satellites formed naturally during the early history of the Solar System.
The Solar System contains hundreds of known moons, ranging from small, irregularly shaped rocks to large worlds bigger than the planet Mercury. Each moon’s characteristics depend on how and where it formed.
How Moons Form
Scientists believe moons form in several different ways:
Co-formation – forming from the same disk of material as the planet
Capture – a planet’s gravity captures a passing object
Impact formation – debris from a collision forms a moon
Earth’s Moon is thought to have formed after a massive impact early in Earth’s history, while many small moons of outer planets were likely captured objects.
Diversity of Moons in the Solar System
Moons vary widely in size, composition, and activity:
Rocky moons – such as Earth’s Moon
Icy moons – such as Europa and Enceladus
Volcanically active moons – such as Io
Atmosphere-bearing moons – such as Titan
Some moons have smooth icy surfaces, while others are heavily cratered or geologically active.
Earth’s Moon
Earth has a single, large moon that plays a crucial role in stabilising Earth’s axial tilt. This stability helps maintain relatively consistent seasons over long periods.
The Moon also causes tides on Earth through gravitational interaction and has strongly influenced Earth’s geological and biological history.
Moons of the Outer Planets
The outer planets possess extensive moon systems:
Jupiter has dozens of moons, including the four large Galilean moons
Saturn hosts many icy moons, including Enceladus
Uranus and Neptune have moons with unusual orbits and compositions
Many of these moons are worlds in their own right, with complex geology and internal structures.
Moons and the Search for Life
Some moons are considered prime candidates in the search for extraterrestrial life:
Europa (Jupiter) – likely has a global subsurface ocean
Enceladus (Saturn) – ejects water-rich plumes into space
Titan (Saturn) – has lakes of liquid hydrocarbons and complex chemistry
These moons contain water, energy sources, and chemical building blocks, making them scientifically significant.
Why Moons Matter
Studying moons helps scientists:
Understand planetary formation
Learn how gravity shapes systems
Identify environments where life might exist
Compare Earth’s Moon with other natural satellites
Moons also help scientists understand the long-term evolution of planetary systems, including those around other stars.
Key Terms Introduced
Natural satellite
Gravity
Tides
Subsurface ocean
Capture
Impact formation