Comparing the Moons

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Learning Intentions

By the end of this topic, you should be able to:

Describe one of the other moons in the Solar System
Compare other moons to our Moon (te Marama).

Glossary

Key terms and definitions.

atmosphere: The layer of gases that surrounds a planet or a moon.

captured asteroid: A space rock that has been pulled in by a planet’s gravity and now orbits it.

crater: A bowl-shaped hole on the surface of a planet or moon, formed by the impact of a meteorite or asteroid.

geyser: A vent that shoots hot water and steam from beneath the ground up into the surface of the moon or planet.

magnetic field: An invisible area around a planet or star where magnetic forces on magnetic substances.

orbit: The path one object takes as it moves around another object in space.

revolution: The movement of one object around another, like Earth orbiting the Sun.

Explore!

Activity: Solar System Scope

Use the interactive below or click on this link to open it in a new window: https://www.solarsystemscope.com/ and click "START"

Take a moment to locate the planets.
Click on Mars, then click 'Explore' to be able to look at Mars and its moons.
- - How many moons does Mars have?
  - Zoom in on the moons. How do these moons look similar to our Moon (te Marama)?
  - How do these moons look different to our Moon (te Marama)?
  - Why do you think Mars' moons might look different from our Moon (te Marama)?

Moons from Other Planets

A moon is a natural object that orbits around a planet. Some are nearly as large as a small planet! Others are asteroids and comets that were moving past a planet and captured by the planet's gravity.

Aside from our Moon and the two small moons revolving around Mars, all other moons in our Solar System revolve around the Gas and Ice Giant planets.

Jupiter has over 95 moons that we've found so far. The most famous are the four Galilean moons - they are the biggest moons of Jupiter and orbits near the plane:

Io is incredibly active with volcanoes constantly erupting, making it one of the most geologically active places in our solar system.
Europa is believed to have a liquid water ocean under its icy surface, which could potentially harbor life. It is covered in ice with huge cracks in it. It is thought that the cracks are caused by a warm, thick ocean underneath.
Ganymede is so big it has its own magnetic field, something usually only found on planets.
Callisto has a heavily cratered surface, suggesting it hasn't changed much in a very long time.

An actual picture taken of Jupiter and one of its moons, Io. This picture was taken by a spacecraft that was sent to Pluto.

An actual picture taken of Saturn and one of its moons, Titan. The picture was taken by a spacecraft that orbited around Saturn and its moons.

Saturn also has at least 146 moons! Of these, the most famous are Titan and Enceladus. They are among the biggest moons in the Solar System and are good candidates for finding life outside of Earth.

Titan is the only moon that has an atmosphere, which is mostly nitrogen with a bit of methane, similar to what we think Earth once had billions of years ago. Titan also has lakes of liquid methane and ethane on the surface - the only place where we know liquid exists on a surface outside of Earth.

Titan (NASA) as seen with visible light.

Titan (NASA) as seen with infrared light.

Enceladus has huge cracks and geysers in the ice, clearly showing warm water exists underneath the frozen, icy surface.
Hyperion is irregular in shape. It is not round and shaped more like a potato. Because of this, it rotates chaotically, tumbling unpredictably through space as it revolves around Saturn.

Enceladus (NASA)

Hyperion (NASA)

Types of Moons

When we look at moons, we can look at the shape and surface to decide key ideas about the moon:

Captured asteroids / comets

These are smaller moons with irregular shapes (not round) and often eccentric orbits, indicating they were not formed alongside their planet. They also tend to have lots of craters. Examples include the moons of Mars, Phobos and Deimos, which are thought to be captured asteroids. These moons are typically made of rock and ice.

Large Moons with a Cold Interior:

These moons are typically icy and have relatively inactive surfaces. They may have a layered structure with an icy crust and a core of rock or ice. They also tend to have lots of craters. Examples include some of the outer moons of Jupiter (Ganymede and Callisto).

Large Moons with a Warm Interior:

These moons can be geologically active, with features like volcanoes, geysers, cracks in the ice or subsurface oceans. They are round. Examples include Io (Jupiter's moon), which is known for its intense volcanism, and Europa (also a Jupiter moon), which is thought to have a subsurface ocean. Titan, Saturn's moon, also has a warm interior and a dense atmosphere, with evidence of liquid methane lakes, rivers, and seas on its surface.

Glossary

Key terms and definitions.

atmosphere: The layer of gases that surrounds a planet or a moon.

captured asteroid: A space rock that has been pulled in by a planet’s gravity and now orbits it.

crater: A bowl-shaped hole on the surface of a planet or moon, formed by the impact of a meteorite or asteroid.

geyser: A vent that shoots hot water and steam from beneath the ground up into the surface of the moon or planet.

magnetic field: An invisible area around a planet or star where magnetic forces on magnetic substances.

orbit: The path one object takes as it moves around another object in space.

revolution: The movement of one object around another, like Earth orbiting the Sun.

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Comparing the Moons

Learning Intentions

Glossary

Explore!

Activity: Solar System Scope

Moons from Other Planets

Types of Moons

Captured asteroids / comets

Large Moons with a Cold Interior:

Large Moons with a Warm Interior:

More on Comparing the Moons

Glossary