The Planets

Navigate the knowledge tree: 🌿 Earth & Space ➡ Astronomy ➡ Our Place in Space

Learning Intentions

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

Name the main types of planets in our Solar System.
Compare the differences between the planets in our Solar System.
Give reasons why planets are different from each other.

Glossary

Key terms and definitions.

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

Gas Giants: Very large planets made mostly of gas; Jupiter and Saturn.

Ice Giants: Large planets made mainly of icy materials and some gas; Uranus and Neptune.

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.

planet (whetūao): A large ball-shaped collection of gas and/or other materials. It does not create its own heat and light.

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

Rocky Planets: Planets with solid, rocky surfaces; Earth, Mars, Venus, and Mercury.

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"

Explore around! Click on two different planets and see if you can find:
- - The average temperature
  - The structure of the planets
  - Three other facts about both planets

Types of Planets

A planet (whetūao) is defined as a round object in space that revolves around a star, and has enough gravity to clear away most nearby objects. It is smaller and less massive than a star, and so it does not make its own light. These planets were each noted by cultures all around the world, and many attempted to understand the meaning behind their movements. Thousands of years later, we now know that the orbit of the planets is what causes them to appear to move compared to the background stars.

There are 3 main types of planets in our Solar System.

- Rocky Planets (Mercury, Venus, Earth and Mars): These planets are relatively close to the Sun, smaller, and are mainly made of rock and metals. They can have different amounts of atmosphere (some or none) with very little hydrogen and helium.
- Gas Giants (Jupiter and Saturn): These large planets are found farther out from the Sun and are made mostly out of hydrogen and helium. The hydrogen and helium atmosphere is extremely thick, but underneath the gas layers are layers where the hydrogen and helium get dense enough to become liquid.
- Ice Giants (Uranus and Neptune): These are similar to the Gas Giants, but are a bit smaller and have less hydrogen and helium (but still much more than the Rocky Planets). Underneath their layers of hydrogen and helium, there is much methane, ammonia and other type of ices, creating a liquid layer that is very different from those of the Gas Giants.

Conditions on Planets

The conditions that we find on a planet depends on several key factors:

Its distance from te Rā. The farther it is; generally the colder it is
The mass of the planet. The more massive it is, the more gravity it has to hold onto an atmosphere
The planet's atmosphere. The more gas there is around a planet, the more likely the light energy from the Sun will get trapped and help warm the planet.
The type of chemicals we find on the planet. Each chemical reacts with the Sun’s energy in different ways, so it can help warm the planet further and potentially also create some reactions within the planet itself.

Other things that can influence the conditions on a planet are: How quickly it rotates, whether it is tilted as it revolves, whether it has a magnetic field or large moons to help protect it from the dangers of space.

Earth is the only planet we know of that has life. What makes our planet so perfect for living things is the conditions we find here. We have the right distance from the Sun, water, air, and nutrients for living things to use. Our magnetic field also protects us from the radiation from the Sun.