Astronomy & Space · Unit 5

The Planets in Depth

Each planet's features, atmospheres, rings and moons

Each planet is a world with its own weather, geology and history, and the differences between them are largely explained by mass, distance from the Sun and what was available where each formed.

The unit takes them in turn - Mercury and Venus, Earth and Mars, Jupiter and Saturn, Uranus and Neptune - along with their moons, several of which are more interesting than the planets they orbit.

This unit breaks down into 21 short steps and 120 questions, starting at difficulty 2 and building to 3. Below you can see exactly what it covers, how the path is structured, and worked examples with explanations.

Steps: 21
Questions: 120
Difficulty: 2-3

What this unit covers

Uranus and Neptune
Jupiter and Saturn
Moons of the Planets
Mercury and Venus
Earth and Mars

Where this fits

Follows Our Solar System. How the Solar System Formed explains why they differ.

Where people slip

Venus is hotter than Mercury despite being further out. Its atmosphere traps heat so effectively that proximity to the Sun stops being the deciding factor.

How the unit is structured

The Planets in Depth runs as 21 short steps that unlock in order. 15 are practice rounds and 6 are challenge rounds that pull together everything before them. Questions start at difficulty 2 and climb to 3 as you progress.

Step 1 · easierStep 21 · harder

Challenge rounds

Example questions

30 real questions from this unit, with the answer and the reason behind it, grouped by what they practise. There are 120 in the unit altogether.

Earth and Mars

Build the sentenceLevel 2
1. Build a true sentence about Mars.
Answer: Mars is called the red planet
Mars is called the red planet because of its rusty soil.
Choose all that applyLevel 2
2. Which of these are true about Earth? (Select all that apply)
- It is the third planet from the Suncorrect
- It is the only planet known to have lifecorrect
- It is the largest planet
- It has no atmosphere
Earth is the third planet and the only world we know of with life.
Fill the blankLevel 2
3. Earth is the ____ planet from the Sun.
- thirdcorrect
- first
- second
- fifth
Earth is the third planet, sitting in just the right spot for liquid water.
Guess the numberLevel 2
4. How many moons does Earth have?
Answer: 1 moons
Earth has just one natural moon.
Fact or fibLevel 3
5. Mars has polar ice caps that grow and shrink with its seasons.
Answer: True
Mars has icy caps at its poles that expand in winter and shrink in summer.
Match the pairsLevel 3
6. Match each Mars feature to what it is.
Answer: Olympus Mons = Giant volcano; Valles Marineris = Huge canyon; Phobos = A moon
Olympus Mons is a volcano, Valles Marineris is a canyon, and Phobos is a moon of Mars.

Jupiter and Saturn

Build the sentenceLevel 2
7. Build a true sentence about Jupiter.
Answer: Jupiter has many large moons
Jupiter has dozens of moons, including four large ones.
Fill the blankLevel 2
8. Jupiter is a giant planet made mostly of ____.
- gascorrect
- solid rock
- ice
- sand
Jupiter is a gas giant, made mostly of hydrogen and helium gas.
Match the pairsLevel 2
9. Match each planet to what it is famous for.
Answer: Saturn = Bright rings; Mars = Red planet; Jupiter = Great Red Spot
Saturn has rings, Mars looks red, and Jupiter has its Great Red Spot storm.
Multiple choiceLevel 2
10. Which is the largest planet in the solar system?
- Jupitercorrect
- Saturn
- Neptune
- Earth
Jupiter is the largest planet, so big that all the other planets could fit inside it.
Choose all that applyLevel 3
11. Which of these are true of the gas giants Jupiter and Saturn? (Select all)
- They are made mostly of hydrogen and heliumcorrect
- They both have ring systemscorrect
- They are rocky like Earth
- They have solid surfaces you could stand on
Both gas giants are made of hydrogen and helium and have rings, but no solid surface to stand on.
Guess the numberLevel 3
12. How many of the eight planets are giant planets (gas or ice giants)?
Answer: 4 planets
Four planets are giants: Jupiter, Saturn, Uranus and Neptune.

Mercury and Venus

Build the sentenceLevel 2
13. Build a true sentence about Venus.
Answer: Venus is the brightest planet
Venus is the brightest planet in our sky, often called the morning or evening star.
Choose all that applyLevel 2
14. Which statements about Venus are true? (Select all)
- It has a thick carbon dioxide atmospherecorrect
- It is the hottest planetcorrect
- It has many large moons
- It is the closest planet to the Sun
Venus has a thick carbon dioxide atmosphere and is the hottest planet, but it has no moons and is second, not first, from the Sun.
Fact or fibLevel 2
15. Mercury is the closest planet to the Sun.
Answer: True
Mercury orbits nearer the Sun than any other planet.
Fill the blankLevel 2
16. Venus is the ____ planet from the Sun.
- secondcorrect
- first
- third
- fourth
Venus is the second planet out from the Sun, just inside Earth's orbit.
Multiple choiceLevel 2
17. Which planet is the hottest in our whole solar system?
- Venuscorrect
- Mercury
- Mars
- Jupiter
Venus is the hottest planet because its thick atmosphere traps heat like a blanket.
Odd one outLevel 2
18. Which of these planets does NOT have any rings?
- Mercurycorrect
- Jupiter
- Saturn
- Uranus
Mercury has no rings, but Jupiter, Saturn and Uranus all do.

Moons of the Planets

Fact or fibLevel 2
19. Titan is the largest moon of Saturn.
Answer: True
Titan is Saturn's biggest moon and even has a thick, hazy atmosphere.
Fill the blankLevel 2
20. Jupiter's four biggest moons were first seen by the astronomer ____.
- Galileocorrect
- Newton
- Copernicus
- Einstein
Galileo discovered Jupiter's four large moons in 1610 with an early telescope.
Match the pairsLevel 2
21. Match each planet to one of its moons.
Answer: Earth = Moon; Mars = Phobos; Saturn = Titan
Earth has the Moon, Mars has Phobos, and Saturn has Titan.
Multiple choiceLevel 2
22. The four largest moons of which planet are called the Galilean moons?
- Jupitercorrect
- Saturn
- Mars
- Neptune
Galileo spotted Jupiter's four big moons in 1610, so we call them the Galilean moons.
Build the sentenceLevel 3
23. Build a true sentence about the biggest moon.
Answer: Ganymede is the largest moon
Ganymede is the largest moon in the solar system.
Choose all that applyLevel 3
24. Which of these are among Jupiter's four Galilean moons? (Select all)
- Iocorrect
- Europacorrect
- Callistocorrect
- Triton
Io, Europa, Callisto and Ganymede are the Galilean moons, but Triton belongs to Neptune.

Uranus and Neptune

Build the sentenceLevel 2
25. Build a true sentence about Neptune.
Answer: Neptune is the farthest planet
Neptune is the farthest planet from the Sun.
Choose all that applyLevel 2
26. Which of these planets are giant planets, not small rocky ones? (Select all)
- Uranuscorrect
- Neptunecorrect
- Mercury
- Mars
Uranus and Neptune are giant planets, while Mercury and Mars are small and rocky.
Fact or fibLevel 2
27. Neptune is a rocky planet just like Earth.
Answer: False
Neptune is not rocky, it is an ice giant made of gas and icy materials.
Fill the blankLevel 2
28. Uranus and Neptune are often called ____ giants.
- icecorrect
- rocky
- super
- dwarf
Uranus and Neptune are called ice giants because they hold lots of icy materials.
Multiple choiceLevel 2
29. Which planet is tipped over so far that it seems to spin on its side?
- Uranuscorrect
- Neptune
- Saturn
- Mars
Uranus is tilted almost completely on its side, so it rolls around the Sun like a ball.
Match the pairsLevel 3
30. Match each planet to a fact about it.
Answer: Uranus = Tilted on its side; Neptune = Windiest planet; Saturn = Brightest rings
Uranus spins on its side, Neptune has the fastest winds, and Saturn has the brightest rings.

Where these questions come from. Each unit starts as a plan of the concepts it should cover and the difficulty it should span. Questions are written against that plan with AI assistance, then checked by a validator that rejects anything without a single defensible answer, an explanation, or plausible wrong options. How we write questions sets out the whole process, and corrections are fixed in the bank and reach the site and the app the same day.

How you practise

This unit mixes 14 different question formats, so you are recalling and applying rather than recognising the same layout every time.

Build the sentence
Choose all that apply
Fact or fib
Fill the blank
Guess the number
Match the pairs
Multiple choice
Odd one out
Picture question
Put in order
Sort into groups
Spell it
True or false
Type the answer

Practise The Planets in Depth

120 questions across 21 steps. Start with step one and crawl at your own pace.

Play this unit

Read about The Planets in Depth

Explainers from our blog on what this unit covers. Each one ends with real questions from the bank.

What Are Saturn's Rings Made Of? Ice, Gaps and a System That May Be YoungSaturn's rings are almost pure water ice, from dust grains to house-sized boulders, in a sheet wider than the Earth-Moon gap. What they are and how they formed.September 14, 2026 · 5 min read

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