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8.2.1Space Physics

The Solar System — Oxford AQA International GCSE Combined Science - Physics Revision Notes & Topical Questions

5 min read 10 parts Lesson 6 of 10

📚 Oxford AQA International GCSE Combined Science - Physics Hub / Topical Revision
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Part 1 of 8Members of the Solar System

Members of the Solar System
Sun
  • Sun the one star at the centre of the Solar System.
Planets
  • Planets eight planets orbit the Sun.
Dwarf planets
  • Dwarf planets smaller planet-like bodies.
Satellites
  • Satellites natural moons and artificial satellites.
Small bodies
  • Small bodies asteroids and comets also orbit the Sun.

Part 2 of 8The eight planets

Order
  • Order in increasing distance from the Sun: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune.
  • Memory aidMy Very Excellent Mother Just Served Us Noodles.
Inner planets
  • Mercury, Venus, Earth and Mars are small and rocky.
Outer planets
  • Jupiter, Saturn, Uranus and Neptune are large gas giants.

Part 3 of 8Dwarf planets

Description
  • Description an object similar to a planet but much smaller.
Gravity
  • Gravity its gravitational field is not strong enough to pull in or clear the nearby objects.
    • (apart from its own natural satellites)
Example
  • Pluto is classed as a dwarf planet.

Part 4 of 8Satellites

Natural satellite
  • Natural satellite an object that orbits a planet, and a moon is one type.
  • The Moon is the natural satellite of the Earth.
Artificial satellite
  • Artificial satellite a man-made object that orbits another object in space.
  • The International Space Station is an artificial satellite that orbits the Earth.

Part 5 of 8Asteroids and comets

Asteroid
  • Asteroid a small rocky object that orbits the Sun.
  • Most lie in the asteroid belt between Mars and Jupiter.
Comet
  • Comet a body of dust and ice that orbits the Sun on a highly elliptical path.
  • Comets are usually found in the outer reaches of the Solar System.
  • Ice melts as a comet approaches the Sun and forms the comet's tail.

Part 6 of 8What orbits what

Orbiting bodyBody it orbits
PlanetThe Sun
MoonPlanet
AsteroidThe Sun
CometThe Sun
Artificial satelliteThe Earth
  • Rule
    • smaller bodies orbit larger ones.

Part 7 of 8Analysing planet data (Extended)

Comparing
  • Comparing values can be compared between planets.
  • Neptune is about 30 times further from the Sun than the Earth.
  • Jupiter has about 320 times the mass of the Earth.
Trend
  • Trend as the distance from the Sun increases, the orbital period increases.
  • Mercury takes 0.24 Earth years and Neptune takes 160 years.
Trend
  • Trend surface temperature generally falls with distance, from about 460 °C on Venus to −220 °C on Neptune.
Anomaly
  • Venus is hotter than Mercury although it is further from the Sun.
Prediction
  • Prediction a value for an unknown body can be estimated by interpolating between known planets.
Surface gravity
  • Surface gravity g depends on the mass and radius of a planet: Mercury 3.7, Venus 8.9, Earth 9.8, Mars 3.7, Jupiter 23.1, Saturn 9.0, Uranus 8.7 and Neptune 11.0 N/kg.

Part 8 of 8More from the specification

1Central gravitational orbital force
  • Central gravitational orbital force mutual gravitational attraction from the massive Sun exerts the centripetal force holding all planets in stable elliptical orbits.
2Rotation of Earth
  • Earth spins once in about 24 hours, causing day and night as each side faces the Sun or turns away.
3Seasons
  • Earth's axis is tilted,
  • so the northern hemisphere gets summer when it is tilted toward the Sun, with longer daylight and stronger solar radiation per area.
4Orbit
  • Earth orbits the Sun in about 365 days, so the southern hemisphere has opposite seasons to the north.
5Light travel
  • Light from the Sun takes about 8 minutes to reach Earth, travelling at 3.0 × 108 m/s.
6Orbital speed
  • Speed of an orbiting planet = circumference of orbit divided by orbital period, v = 2πr/T.
7Rotation of Earth
  • Earth spins once in about 24 hours, causing day and night as each side faces the Sun or turns away.
8Seasons
  • Earth's axis is tilted,
  • so the northern hemisphere gets summer when it is tilted toward the Sun, with longer daylight and stronger solar radiation per area.
9Orbit
  • Earth orbits the Sun in about 365 days, so the southern hemisphere has opposite seasons to the north.
10Light travel
  • Light from the Sun takes about 8 minutes to reach Earth, travelling at 3.0 × 108 m/s.
11Orbital speed
  • Speed of an orbiting planet = circumference of orbit divided by orbital period, v = 2πr/T.
12Orbital speed
  • Speed of an orbiting object, √(GM/r).
13Field strength
  • G = Fg/m.
14Kinetic energy
  • K = ½mv2, energy of motion.
15Gravitational potential
  • Work done per unit mass in bringing a test mass from infinity to the point.
16Potential energy
  • Energy stored by the configuration of a system.
17Hemisphere
  • Half of the Earth, northern or southern.
18Nebula
  • Cloud of gas and dust in which stars form.

Key terms

TermMeaning
Solar SystemThe Sun and all the bodies that orbit it.
PlanetA large body that orbits the Sun and whose gravity clears its orbit.
Dwarf planetA small planet-like body that has not cleared its orbit, such as Pluto.
AsteroidA small rocky body orbiting the Sun, mostly in the asteroid belt.
CometAn icy body on a highly elliptical orbit around the Sun.
Natural satelliteA moon orbiting a planet.
Artificial satelliteA man-made object orbiting a body in space.

Avoid these mistakes

1
Pluto is the ninth planet — it is classed as a dwarf planet.
2
Comets orbit in circles — they have highly elliptical orbits.
3
The asteroid belt lies beyond Neptune — it lies between Mars and Jupiter.
4
A moon orbits the Sun directly — a moon orbits its planet.

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