The Outer Planets — An Overview
Our solar system has eight planets divided into two main groups. The four inner planets (Mercury, Venus, Earth, Mars) are small and rocky. The four outer planets are very different — they are enormous balls of gas and ice, much larger than anything in the inner solar system.
The outer planets, in order from the Sun, are:
- Jupiter (5th from the Sun)
- Saturn (6th from the Sun)
- Uranus (7th from the Sun)
- Neptune (8th from the Sun)
These four are often called the gas giants (or for Uranus and Neptune, ice giants). They have no solid surface to stand on, they spin faster than inner planets, but they take much longer to orbit the Sun because they are so far away.
Two important movements to understand:
- Rotation — a planet spinning on its own axis (this gives us day and night). Also called a planet's day length.
- Revolution — a planet travelling all the way around the Sun (this gives us a year). Also called its orbital period.
Don't mix these up! A planet can spin quickly (short day) while still taking a very long time to go around the Sun (long year).
Jupiter — The Giant of the Solar System
Jupiter is the largest planet in our solar system — so large that more than 1,300 Earths could fit inside it!
A large planet made mostly of gas (hydrogen and helium) with no solid surface. Jupiter and Saturn are the two classic gas giants in our solar system.
Key facts about Jupiter:
- Position: 5th planet from the Sun
- Moons: At least 95 confirmed moons (including the four large Galilean moons: Io, Europa, Ganymede, Callisto) — moon counts are updated as new discoveries are made!
- Atmosphere: Layers of colourful clouds — white, brown, orange, and red — whipped into swirling bands by powerful winds
- Great Red Spot: A massive storm (technically an anticyclone — a giant spinning high-pressure system) that has been raging for hundreds of years
- Day length: Less than 10 hours (Jupiter spins very fast!)
- Year length: About 4,333 Earth days (nearly 12 Earth years)
- Cloud-top temperature: About
Think of Jupiter's Great Red Spot like the most powerful storm you can imagine — except this one is so enormous that the entire Earth could fit inside it, and it has been spinning for hundreds of years! Unlike a hurricane on Earth (which is a low-pressure system), Jupiter's Great Red Spot is a high-pressure anticyclone, but both are gigantic rotating storm systems.
Scientists believe Jupiter has no solid surface at all. Deep inside, the gas is compressed under such extreme pressure that it becomes liquid. There is no ground to land on!
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