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IB DemystifiedMYP Sciences

The solar system

Our home is one small rocky planet among eight, circling an ordinary star. From scorching Venus to icy Neptune, the solar system is full of patterns, surprises and hazards, and it is far bigger than most pictures suggest.

Recommended for MYP 2 · About 3 lessons · Criteria A, B, C and D

SunMercuryVenusEarthMarsJupiterSaturnUranusNeptuneSizes to scale (Mercury and Mars enlarged slightly so they can be seen); distances NOT to scale.
Figure 1. The planets are very different sizes, and their distances from the Sun are enormous.
On this page
  1. Learning objectives
  2. Before you start
  3. Key vocabulary
  4. Understanding the ideas
  5. The planets in order
  6. The solar system in the real world
  7. Worked examples
  8. Assessment tips
  9. Check your understanding
  10. Practice questions
  11. Investigation
  12. Criterion-linked questions
  13. Challenge questions
  14. Topic check
  15. Review your mistakes
  16. Your progress

Learning objectives

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

  • describe the Sun, planets, moons, asteroids, comets and dwarf planets
  • use planet data to find patterns
  • work with scale and large distances
  • explain that gravity keeps objects in orbit
  • analyse model experiments and plan fair tests
  • discuss asteroid defence and space debris

Before you start

You will use these skills. If any feel shaky, review them first.

  • forces and gravity (see Forces and their effects)
  • light (reflection and shadows)
  • large numbers and division

Key vocabulary

Solar system
The Sun and everything that orbits it.
Planet
A large, round object that orbits the Sun and has cleared its path of other objects.
Orbit
The curved path of one object around another.
Moon
A natural object that orbits a planet.
Asteroid
A rocky object orbiting the Sun, mostly between Mars and Jupiter.
Comet
An icy object that grows a glowing tail near the Sun.

Understanding the ideas

  1. What is it?

    The solar system is the Sun and all the objects held in orbit by its gravity: eight planets and their moons, dwarf planets such as Pluto, asteroids and comets.

  2. Why does it happen?

    The four inner planets are small and rocky; the four outer planets are giants made mostly of gas and ice. Further planets take longer to orbit and are generally colder, because they receive much less sunlight, but atmospheres matter too: Venus is the hottest planet because its thick carbon dioxide atmosphere traps heat.

  3. How do we know?

    Astronomers use telescopes, space probes and landers to study the planets. Missions have landed on Mars, flown past every planet, and even changed the orbit of an asteroid.

  4. Why does it matter?

    Studying the solar system helps us understand Earth, protect it from asteroids, and use satellites for weather, communication and navigation, while keeping space safe from debris.

  5. What does it connect to?

    This topic links to gravity and forces in physics, to light, and later to stars, the universe, days and seasons.

The planets in order

  • Mercury: smallest planet, closest to the Sun.
  • Venus: hottest planet (thick CO₂ atmosphere).
  • Earth: liquid water and life.
  • Mars: cold, red, rocky.
  • Jupiter: largest planet, a gas giant.
  • Saturn: gas giant with bright rings.
  • Uranus and Neptune: ice giants, extremely cold and far away.

A memory aid: My Very Easy Method Just Speeds Up Naming.

The solar system in the real world

Pakistan's first lunar satellite, ICUBE-Q, travelled to the Moon in 2024. Weather satellites orbiting Earth help forecast monsoon rains and floods. Astronomers track near-Earth asteroids so that any danger is spotted years in advance.

Worked examples

Example 1: a planet's year

Mars takes 1.88 Earth years to orbit the Sun. How many Earth days is that? (1 year = 365 days)

  1. 1.88 × 365.
  2. = 686 Earth days.

Example 2: scale

In a model, 1 cm represents 1000 km. How wide should model Earth (12 756 km) be?

  1. 12 756 ÷ 1000 = 12.756.
  2. About 12.8 cm wide.

Assessment tips

Solar system questions often use tables of planet data and diagrams. Expect to:

  • Describe the objects in the solar system and their features.
  • Use data to find patterns and exceptions.
  • Calculate with scale, ratios and large numbers.
  • Explain orbits using gravity.

Common mistakes: saying there is no gravity in space; saying the Moon makes its own light; confusing a day with a year; and assuming pictures show distances to scale.

Check your understanding

Quick questions on the ideas above. Try each one before using a hint.

Practice questions

Show

Investigation: a scale model of the solar system

Partially guided investigation · about 50 minutes · groups, outdoors

Research question
If the Sun is shrunk to the size of a football, where should each planet be placed, and how big should it be?
Scientific background
Pictures of the solar system squash huge distances. A scale model shows how far apart the planets really are compared with their sizes.
Hypothesis
Write your own prediction, with a scientific justification.
Variables
Identify your independent, dependent and control variables, and explain how you will control them.
Apparatus
A football (the Sun), small objects such as seeds and beads for planets, a long measuring tape or trundle wheel, calculators, a large open space.
Method
  1. Use the scale: if the Sun is 22 cm wide, 1 cm in the model represents about 63 000 km.
  2. Calculate each planet's model size and model distance from the Sun.
  3. Place the Sun at one end of the field and pace out each planet's distance.
  4. Compare how far away Neptune is with how big it is.

Safety. Stay within the school grounds, watch out for others, and do not run while measuring.

Then evaluate: why is it almost impossible to show both sizes and distances to scale on one page?

Criterion-linked questions

Criterion B: inquiring and designing

Criterion C: processing and evaluating

Criterion D: reflecting on the impacts of science

Challenge questions

Harder problems in unfamiliar contexts. Plan before you calculate.

Topic check

Five questions picked at random from the whole topic. Take a new set whenever you like.

Review your mistakes

Questions you got wrong on this device appear here so you can try them again. Answer one correctly and it leaves the list.

Your progress

Tracked separately for each skill, on this device only.

SkillCorrectStatus

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