Our solar system — AQA GCSE Physics

Module 8 · Lesson 8.01 · Spec 4.8.1.1

Our Solar System and Beyond

What's in the solar system, where it sits in the universe, and how the Sun came to be.

Physics-only · Paper 2

What you'll learn

Spec 4.8.1.1Paper 2Physics-only

By the end you'll be able to

List the contents of our solar system.

Distinguish natural satellites from artificial satellites.

Place the solar system within the Milky Way galaxy and the universe.

Explain how the Sun formed from a nebula by gravitational attraction.

Describe the equilibrium between gravity and fusion-driven expansion in a main sequence star.

Why it matters

Paper 2 always carries Space questions. This first lesson is the foundation: get the vocabulary right and you protect easy marks every paper.

What's in our solar system

Solar System

The system of objects in orbit around our Sun. Held together by the Sun's gravity.

The full inventory — these are the categories examiners want named:

The Sun — one main sequence star, at the centre.

Eight planets — in approximately circular orbits.

Dwarf planets — e.g. Pluto, Ceres.

Asteroids — rocky bodies, mostly between Mars and Jupiter.

Comets — icy bodies, in highly elliptical orbits.

Natural satellites (moons) — orbiting planets.

Not to scale. Me=Mercury · V=Venus · E=Earth · Ma=Mars · J=Jupiter · S=Saturn · U=Uranus · N=Neptune.

The eight planets — in order from the Sun

1MERCURY

2VENUS

3EARTH

4MARS

5JUPITER

6SATURN

7URANUS

8NEPTUNE

Inner (rocky)

Mercury, Venus, Earth, Mars — small, dense, solid surfaces.

Outer (gas giants)

Jupiter, Saturn, Uranus, Neptune — massive, mostly hydrogen and helium.

Mnemonic

My Very Educated Mother Just Served Us Noodles.

The Sun — a main sequence star

Main Sequence Star

A stable star in which gravity pulling inward is balanced by radiation pressure from fusion pushing outward. The Sun is currently in this stage and has been for ~4.6 billion years.

What the Sun does

Sits at the centre of the solar system — everything orbits it.

Fuses hydrogen into helium in its core (nuclear fusion).

Is the source of energy for the whole solar system (light, heat).

Holds the system together with its gravity.

Exam vocab

If asked "what type of star is the Sun?" the correct answer is main sequence (not "yellow", not "small", not "average").

How the Sun formed

The Sun was formed from a cloud of dust and gas (nebula) pulled together by gravitational attraction. — AQA spec 4.8.1.1

NEBULA cloud of dust & gas

GRAVITY PULLS cloud collapses

PROTOSTAR heats up

FUSION IGNITES main sequence

Step by step

A nebula — a vast cloud of dust and gas (mostly hydrogen) — exists in space.

Gravity pulls the material together. As it collapses, it heats up.

A dense, hot core forms: a protostar.

When the core is hot and dense enough, hydrogen fusion ignites. The star joins the main sequence.

Why a star is stable — equilibrium

Fusion reactions lead to an equilibrium between the gravitational collapse of a star and the expansion of a star due to fusion energy. — AQA spec 4.8.1.1

The mechanism

Gravity pulls all the star's mass inward — tries to collapse it.

Fusion in the core releases huge energy, creating an outward radiation pressure.

The two forces balance — the star is in equilibrium and stays stable for billions of years.

Smaller bodies in the solar system

TypeDescriptionWhere found

Dwarf planetA body that orbits the Sun but isn't classed as a full planet (hasn't cleared its orbital neighbourhood).Pluto (reclassified 2006), Ceres, Eris.

AsteroidA small rocky body left over from solar system formation.Mostly in the asteroid belt between Mars and Jupiter.

CometAn icy body that develops a tail when it nears the Sun.Highly elliptical orbits — far from the Sun most of the time.

Worth knowing

Comets orbit the Sun on highly elongated paths. Asteroids stay in a narrow band. Both are part of the solar system — both can be named as "types of object" in spec questions.

Natural satellites — moons

Natural Satellite

A naturally occurring object that orbits another, larger body. Moons orbiting planets are the classic example.

Examples in our solar system

Earth has 1 moon (the Moon).

Mars has 2 small moons (Phobos, Deimos).

Jupiter has dozens of moons, including the four big "Galilean" moons: Io, Europa, Ganymede, Callisto.

Saturn has many moons too — Titan is the largest.

Mercury and Venus have no moons.

Spec wording

The spec says: "Natural satellites, the moons that orbit planets, are also part of the solar system." Memorise this exact equivalence — moons = natural satellites.

Artificial satellites — man-made

Artificial Satellite

A man-made object placed in orbit around the Earth (or another body) for a specific purpose.

TypePurpose

International Space Station (ISS)Crewed research laboratory in low Earth orbit.

Hubble Space TelescopeObserving distant stars and galaxies from orbit (above Earth's atmosphere).

GPS satellitesPosition and navigation (used by phones, cars, planes).

Weather satellitesImaging clouds, tracking storms, forecasting.

Communications satellitesTV, phone, internet relay.

(Note: artificial satellites orbit Earth — they're not part of the natural solar system inventory in the strict spec sense, but they are still "satellites" and you must know the term.)

Natural vs artificial — the key distinction

Natural satellites

Naturally occurring

Formed alongside the planet

Example: the Moon, Io, Titan

Single word: moons

Artificial satellites

Built by humans

Launched and placed in orbit

Example: ISS, GPS, Hubble

Have a specific purpose

Common confusion

Both are called satellites. The word "satellite" alone doesn't tell you which type — you must specify natural or artificial in your answer.

Where the solar system fits — scale

Our solar system is a small part of the Milky Way galaxy. — AQA spec 4.8.1.1

1 starSolar system1 Sun + 8 planets + smaller bodies. Held together by Sun's gravity.

~10¹¹ starsMilky Way galaxyHundreds of billions of stars bound by gravity. Our solar system is a small part of it.

~10¹¹ galaxiesUniverseBillions of galaxies. All of space, time, matter, and energy.

Measuring cosmic distance — light years

Light Year

The distance that light travels in one year. Approximately 9.5 × 10¹⁵ m.

~8 min

Light from Sun to Earth

~4.2 ly

Nearest star (Proxima Centauri)

~10⁵ ly

Across the Milky Way

Why light years?

Cosmic distances are enormous — using metres gives unwieldy huge numbers.

Light years compress these into manageable figures (4 ly, 100 000 ly, etc.).

They also tell you something physical: how long the light you see has been travelling.

Conversion fluency

1 ly ≈ 9.5 × 10¹⁵ m. Be ready to convert: if a galaxy is 5 ly away, that's 5 × 9.5 × 10¹⁵ = 4.75 × 10¹⁶ m.

Examiner alert — Jun 2024

Question pattern

Jun 2024 Paper 2, Q3.1:

"The Sun is the star at the centre of our solar system. Give three other types of object that form our solar system."3 marks

~50%

Scored all 3 marks

~35%

Scored 2 of 3

~15%

Scored 0 or 1

What lost marks (verified from examiner report)

Repeating "the Sun" or naming stars (it's already given).

Failing to distinguish natural satellites from artificial ones — examiner report flagged this directly.

Listing stages in the life cycle of a star (red giant, white dwarf, etc.) — these are not objects in our solar system.

Vague answers like "things in space" or just "satellites".

How to answer — weak vs strong

Same question: "Give three other types of object that form our solar system."3 marks

Weak

"Satellites, planets, things"

"Satellites" — too vague (which type?)

"Things" — not a category at all

Probable mark: 1/3

Strong

"Planets, dwarf planets, asteroids"

Three distinct, named categories

Each is a recognised solar system object type

Probable mark: 3/3

Other valid choices (Jun 2024 mark scheme)

Any three from: planets · dwarf planets · moons (or natural satellites). Also accepted: asteroids · comets · meteors · meteoroids · meteorites. Avoid "satellites" without "natural" — and never write "artificial satellites" here (not credited).

Practice — exam-style

Q1. Define what is meant by a natural satellite, and give one example. 2 marks

Model answer

A naturally occurring object that orbits a planet (or: a larger body). [1]

Example: the Moon (orbiting Earth) — or Io, Europa, Titan, Phobos, etc.[1]

Q2. Describe how the Sun formed. 3 marks

Model answer

The Sun formed from a nebula — a cloud of dust and gas. [1]

The cloud was pulled together by gravitational attraction. [1]

As it collapsed it heated up until fusion ignited in the core. [1]

Common errors to avoid

ErrorCorrect versionWhy

"Pluto is a planet"Pluto is a dwarf planetReclassified in 2006 — there are 8 planets, not 9.

"The universe is our galaxy"The universe contains billions of galaxies; the Milky Way is just one.Scale matters — galaxy ≠ universe.

"Satellites" (unqualified) when asked for objectsSpecify natural (moon) or artificial (man-made)Both exist; the spec requires the distinction.

"The Sun is a yellow dwarf" / "small star" / "average star"The Sun is a main sequence star"Yellow dwarf" is scientifically valid but not the AQA spec term — examiners want "main sequence". Use the spec wording.

"Gravity is the only force in a star"Gravity (inward) balances radiation pressure from fusion (outward)Without the balance, the star would collapse instantly.

Checkpoint

You can now:

List the contents of the solar system: Sun, 8 planets, dwarf planets, asteroids, comets, moons.

Name the 8 planets in order from the Sun.

Identify the Sun as a main sequence star .

Explain that the Sun formed from a nebula pulled together by gravitational attraction .

Describe the equilibrium between gravity (inward) and radiation pressure from fusion (outward).

Distinguish natural satellites (moons) from artificial satellites (ISS, GPS).

Place the solar system within the Milky Way galaxy, and the galaxy within the universe.

State that 1 light year ≈ 9.5 × 10¹⁵ m .

Lesson summary & what's next

The headline facts

Solar system: Sun + 8 planets + dwarf planets + asteroids + comets + moons.

Sun: main sequence star, formed from a nebula by gravity.

Equilibrium: gravity in = radiation pressure out → stable star.

Satellites: natural (moons) vs artificial (man-made).

Hierarchy: solar system ⊂ Milky Way galaxy ⊂ universe.

Distance: 1 ly ≈ 9.5 × 10¹⁵ m.

Coming next: 8.02

The life cycle of a star — what happens after the main sequence. Two paths depending on mass. One of Paper 2's most reliable 6-mark Level of Response topics.