IGCSE Physics Solar System Questions and Worked Solutions (6.1.2) | 0625

By /
IGCSE Physics 0625 · Topic 6.1.2

IGCSE Physics Solar System Questions and Worked Solutions

50 topic-wise practice questions on The Solar System (Unit 6: Space Physics), written to the Cambridge IGCSE Physics 0625 syllabus for 2026–2028, each with a step-by-step worked solution.

50 questions26 Core14 Extended10 Challenge130 marksTextbook §6.1 · pp. 276–285
Questions tagged Core are for all candidates (Papers 1 & 3). Questions tagged Extended are Supplement content (Papers 2 & 4). Questions 41–50 are harder Challenge questions. Try each question first, then tap Show solution to check your working.

Topic guide: The Solar System

The Solar System contains the Sun, eight planets, minor planets, moons and smaller bodies. The accretion model explains why inner planets are rocky and outer planets are gaseous. Gravity from the massive Sun keeps everything in orbit.

Key formulas

t = d ÷ ctime for light to travel a distance (c = 3.0 × 10⁸ m/s)Core

Prerequisite knowledge

  • Weight and gravitational field strength (1.3)
  • Speed of light (3.3)
  • Energy conservation (1.7.1, Extended)

Exam tips & common mistakes

  • Learn the planet order with a mnemonic
  • Use metres and seconds for light-travel time
  • Describe trends from data with numbers

Key facts from the syllabus (6.1.2)

  • Contents: one star (the Sun), eight planets (Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune), minor planets (dwarf planets e.g. Pluto, asteroids), moons, comets
  • Inner four planets are small and rocky; outer four are large and gaseous — explained by an accretion disc model (gravity, elements in gas/dust clouds, rotation)
  • Gravitational field strength at a planet's surface depends on its mass and decreases with distance
  • The Sun contains most of the mass, so the planets orbit it; the force is the Sun's gravitational attraction
  • Extended orbits are elliptical with the Sun not at the centre (unless nearly circular)
  • Extended the Sun's field and planets' orbital speeds decrease with distance from the Sun
  • Extended in an elliptical orbit an object is fastest when closest to the Sun (energy conservation)
  • Extended analyse planetary data — orbital distance, period, density, surface temperature, surface g

Textbook: §6.1 Earth and the Solar System, pp. 276–285

1
Core[2 marks]

List the eight planets in order from the Sun.

Show solutionHide solution

Method: Mnemonic.

Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune
2
Core[2 marks]

Name two types of minor planet in the Solar System.

Show solutionHide solution

Method: Dwarf planets, asteroids.

Dwarf planets (e.g. Pluto) and asteroids (in the asteroid belt)
3
Core[1 mark]

State what a moon is.

Show solutionHide solution

Method: Natural satellite of a planet.

A natural satellite that orbits a planet
4
Core[2 marks]

Compare the four inner planets with the four outer planets.

Show solutionHide solution

Method: Rocky/small vs gas/large.

Inner: small and rocky; outer: large and gaseous
5
Core[3 marks]

Explain, using the accretion model, why the inner planets are rocky.

Show solutionHide solution

Method: Hot near Sun, only rock condenses.

A rotating disc of gas and dust formed around the Sun; near the hot Sun only rocky material could condense, and gravity pulled it together into small rocky planets
6
Core[2 marks]

State the role of gravity in the accretion model.

Show solutionHide solution

Method: Pulls material together.

Gravity pulls dust and gas together to form the Sun and the planets
7
Core[2 marks]

State two factors the gravitational field strength around a planet depends on.

Show solutionHide solution

Method: Mass, distance.

The mass of the planet; the distance from the planet
8
Core[3 marks]

The distance from the Sun to the Earth is 1.5 × 10¹¹ m. Calculate the time for light to reach the Earth.

Show solutionHide solution

Method: t = d/c.

t = 1.5×10¹¹ ÷ 3.0×10⁸ = 500 s
9
Core[3 marks]

Jupiter is 7.8 × 10¹¹ m from the Sun. Calculate the time for sunlight to reach Jupiter in minutes.

Show solutionHide solution

Method: t = d/c.

t = 2600 s = 43.3 min
10
Core[3 marks]

The Moon is 3.8 × 10⁸ m from Earth. Calculate the time for a radio signal to reach the Moon and return.

Show solutionHide solution

Method: Round trip.

t = 2 × 3.8×10⁸ ÷ 3.0×10⁸ = 2.53 s
11
Core[2 marks]

Explain why the planets orbit the Sun.

Show solutionHide solution

Method: Sun has most mass.

The Sun contains most of the mass of the Solar System, so its gravitational attraction keeps the planets in orbit
12
Core[1 mark]

Name the force that keeps an object in orbit around the Sun.

Show solutionHide solution

Method: Gravity.

The gravitational attraction of the Sun
13
Core[2 marks]

Name the largest planet in the Solar System.

Show solutionHide solution

Method: Jupiter.

Jupiter
14
Core[2 marks]

Name the planet closest to the Sun.

Show solutionHide solution

Method: Mercury.

Mercury
15
Core[2 marks]

State where the asteroid belt is found.

Show solutionHide solution

Method: Mars–Jupiter.

Between the orbits of Mars and Jupiter
16
Core[2 marks]

Name a dwarf planet.

Show solutionHide solution

Method: Pluto.

Pluto (or Ceres, Eris)
17
Core[2 marks]

State what a comet is made of.

Show solutionHide solution

Method: Ice and dust.

Ice, dust and rock
18
Core[2 marks]

Name the four rocky planets.

Show solutionHide solution

Method: Inner four.

Mercury, Venus, Earth, Mars
19
Core[2 marks]

Name the four gas giants.

Show solutionHide solution

Method: Outer four.

Jupiter, Saturn, Uranus, Neptune
20
Core[3 marks]

Explain why the outer planets are large and gaseous, using the accretion model.

Show solutionHide solution

Method: Cold region, gases condense.

Far from the Sun it was cold enough for gases and ices to condense; large amounts of material gathered by gravity into large gaseous planets
21
Core[2 marks]

State why material in the early Solar System formed a flat disc.

Show solutionHide solution

Method: Rotation.

The cloud was rotating, so it flattened into an accretion disc
22
Core[2 marks]

Explain why gravitational field strength is greater on Jupiter than on Earth.

Show solutionHide solution

Method: Larger mass.

Jupiter has a much larger mass
23
Core[2 marks]

State how the gravitational field around a planet changes with distance.

Show solutionHide solution

Method: Decreases.

It decreases with distance
24
Core[3 marks]

Mars is 2.3 × 10¹¹ m from the Sun. Calculate the time for light from the Sun to reach Mars.

Show solutionHide solution

Method: t = d/c.

t = 767 s
25
Core[3 marks]

Neptune is 4.5 × 10¹² m from the Sun. Calculate the time for sunlight to reach it in hours.

Show solutionHide solution

Method: t = d/c.

t = 15000 s = 4.17 h
26
Core[3 marks]

A radio signal takes 20 minutes to reach a Mars rover. Calculate the distance.

Show solutionHide solution

Method: d = ct.

d = 3.0×10⁸ × 1200 = 3.6 × 10¹¹ m
27
Extended[2 marks]

Describe the shape of the orbits of planets and comets.

Show solutionHide solution

Method: Elliptical.

Elliptical, with the Sun not at the centre (except for nearly circular orbits)
28
Extended[2 marks]

State how the orbital speed of planets changes with distance from the Sun.

Show solutionHide solution

Method: Decreases.

It decreases as the distance from the Sun increases
29
Extended[3 marks]

Explain, using conservation of energy, why a comet travels fastest when closest to the Sun.

Show solutionHide solution

Method: GPE → KE.

As it falls towards the Sun, gravitational potential energy decreases and kinetic energy increases, so it moves fastest at its closest point
30
Extended[2 marks]

State how the Sun's gravitational field strength changes with distance.

Show solutionHide solution

Method: Decreases.

It decreases as distance increases
31
Extended[3 marks]

Planet data: Mercury 0.39 AU, 88 days; Mars 1.52 AU, 687 days. Describe the trend between orbital distance and period.

Show solutionHide solution

Method: Further → longer.

The greater the orbital distance, the longer the orbital period
32
Extended[3 marks]

Planet A has surface g = 3.7 N/kg and planet B has g = 24.8 N/kg. Suggest which is more massive if they have similar radii and explain.

Show solutionHide solution

Method: g depends on mass.

Planet B: a larger surface gravitational field strength means greater mass
33
Extended[2 marks]

From data, inner planets have densities about 4–5.5 g/cm³ and outer planets about 0.7–1.6 g/cm³. Explain this.

Show solutionHide solution

Method: Rocky vs gaseous.

Inner planets are rocky (dense); outer planets are mostly gas (low density)
34
Extended[2 marks]

Explain why surface temperature generally decreases for planets further from the Sun.

Show solutionHide solution

Method: Less radiation received.

They receive less energy per square metre from the Sun
35
Extended[2 marks]

State where the Sun is located in a planet's elliptical orbit.

Show solutionHide solution

Method: Not centre.

At one focus, not at the centre
36
Extended[3 marks]

A comet travels at 50 km/s near the Sun and 5 km/s far away. Explain this using energy.

Show solutionHide solution

Method: GPE ↔ KE.

Near the Sun it has lost gravitational potential energy, which has become kinetic energy, so it moves faster; far away GPE is high and KE low
37
Extended[3 marks]

Planet data: Earth 1.0 AU, 30 km/s; Jupiter 5.2 AU, 13 km/s; Neptune 30 AU, 5.4 km/s. Describe the pattern.

Show solutionHide solution

Method: Speed decreases.

Orbital speed decreases as distance from the Sun increases
38
Extended[2 marks]

Explain why outer planets have lower orbital speeds.

Show solutionHide solution

Method: Weaker gravity.

The Sun's gravitational field is weaker further away, so less speed is needed for orbit
39
Extended[3 marks]

Data: planet X has surface g = 3.7 N/kg, planet Y has g = 11 N/kg. A 70 kg astronaut visits both. Calculate the weight on each.

Show solutionHide solution

Method: W = mg.

X: 259 N; Y: 770 N
40
Extended[2 marks]

Explain why a planet's surface temperature data may not fit the distance pattern exactly (e.g. Venus hotter than Mercury).

Show solutionHide solution

Method: Atmosphere.

Venus's thick CO₂ atmosphere causes a strong greenhouse effect

Challenge questions

Harder, multi-step questions at the top end of the exam. Attempt these once you are confident with the questions above.

41
ChallengeCore[4 marks]

Using the accretion model, explain why the inner planets are small and rocky while the outer planets are large and gaseous.

Show solutionHide solution

Method: Temperature in the disc.

A rotating cloud of gas and dust formed an accretion disc; near the hot young Sun only rock and metal could condense, forming small rocky planets; further out, cold enough for ices and gases, more material gathered under gravity into large gaseous planets
42
ChallengeCore[4 marks]

Light from the Sun takes 8.3 minutes to reach the Earth. Calculate the Earth–Sun distance and how long light takes to reach Saturn at 1.4 × 10¹² m.

Show solutionHide solution

Method: d = ct.

d = 1.5 × 10¹¹ m; Saturn: 4670 s = 77.8 min
43
ChallengeCore[4 marks]

Radio signals from a probe near Neptune (4.5 × 10¹² m from Earth) are received. Calculate the delay and explain why the probe must be controlled by pre-programmed instructions.

Show solutionHide solution

Method: Delay.

t = 15000 s ≈ 4.17 h; a round-trip of 8 h is too long for real-time control
44
ChallengeCore[3 marks]

Explain why the Sun's gravity holds the planets in orbit, referring to its mass.

Show solutionHide solution

Method: Mass dominates.

The Sun contains most of the Solar System's mass, so its gravitational attraction is by far the strongest force on each planet
45
ChallengeCore[3 marks]

Explain how the gravitational field strength at a planet's surface depends on the planet's mass, and how the field changes with distance from the planet.

Show solutionHide solution

Method: Mass and distance.

Larger mass gives a stronger surface field; the field decreases with distance from the planet
46
ChallengeExtended[4 marks]

Explain, using energy conservation, why a comet in a highly elliptical orbit moves fastest when closest to the Sun.

Show solutionHide solution

Method: GPE → KE.

As the comet falls inwards, gravitational potential energy is converted to kinetic energy, so it speeds up; moving outwards it slows as kinetic energy becomes potential energy
47
ChallengeExtended[5 marks]

Planet data: Mercury 58 million km, 48 km/s; Earth 150, 30 km/s; Mars 228, 24 km/s; Jupiter 778, 13 km/s. Describe and explain the trend.

Show solutionHide solution

Method: Gravity weakens with distance.

Orbital speed decreases with distance: the Sun's gravitational field is weaker further out, so a smaller speed is enough for a stable orbit
48
ChallengeExtended[4 marks]

A planet has surface g = 24.8 N/kg; another has 3.7 N/kg. A 75 kg astronaut's weight is measured on each. Calculate both weights and suggest which planet is more massive and why, assuming similar radii.

Show solutionHide solution

Method: W = mg.

1860 N and 278 N; the first planet is more massive
49
ChallengeExtended[4 marks]

Explain why Venus has a higher surface temperature than Mercury although it is further from the Sun.

Show solutionHide solution

Method: Atmosphere.

Venus has a thick CO₂ atmosphere causing a strong greenhouse effect; Mercury has almost no atmosphere to trap energy
50
ChallengeExtended[3 marks]

Explain where the Sun is located in an elliptical orbit and when the Sun would be at the centre.

Show solutionHide solution

Method: Focus.

At one focus, not the centre; it is at the centre only when the orbit is (approximately) circular
All IGCSE Physics topics← 6.1.1 The Earth6.2.1 The Sun as a Star →

Book a free trial class

Tell us a little about your requirement.