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6.1.3Space Physics

Formation of the Solar System — Cambridge IGCSE Physics 0625 Revision Notes & Topical Questions

5 min read 11 parts Lesson 8 of 24 1 quiz

📚 Cambridge IGCSE Physics 0625 Hub / Topical Revision
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6.1.3 Formation of the Solar System — IGCSE Physics Notes — IGCSE PHYSICS notes: Describe how the Sun and planets formed from a cloud of gas and dust and explain why the inner and outer planets differ.Nebula — a huge interstellar cloud of gas and dust, mainly hydrogen and helium.…

  • Heavy elements
  • Heating effect
  • Same plane
  • Accretion disc
  • Nuclear fusion
  • Hemisphere

Part 1 of 9The starting point: a nebula

Nebula
  • Nebula a huge interstellar cloud of gas and dust, mainly hydrogen and helium.
Age
  • Age the Solar System formed about 4.5 billion years ago.
Heavy elements
  • Heavy elements the nebula held elements made in an earlier supernova explosion, such as carbon, oxygen, silicon and iron.
  • The Earth and everything on it is built from recycled star material.

Part 2 of 9Collapse under gravity

Trigger
  • Trigger part of the cloud began to contract under its own gravity.
  • A shock wave from a nearby exploding star may have disturbed it.
Spinning
  • Spinning as the cloud collapsed it spun faster and flattened into a rotating accretion disc.
Heating
  • Heating the centre became denser and hotter as gravitational potential energy was transferred to thermal energy.
Protostar
  • Protostar the dense central ball was a protostar that shone because it was hot, not because of fusion.

Part 3 of 9Birth of the Sun

Fusion
  • Fusion when the core temperature reached about 10 million °C, hydrogen nuclei fused to form helium and released energy.
Balance
  • Balance gravity pulling inwards was balanced by the pressure from the hot gas pushing outwards.
Result
  • Result the collapse stopped and the Sun became a stable star, as it has been for about 4.6 billion years.

Part 4 of 9Accretion of the planets

Accretion
  • Accretion gravitational attraction between particles made them join and grow into larger objects.
Growth
  • Growth grains stuck together to form lumps, then larger bodies that attracted more material.
Planets
  • Planets over millions of years these built up into the planets in the accretion disc.
Clearing
  • Clearing each planet's gravity pulled in or swept away the debris near its orbit.

Part 5 of 9Why the inner planets are rocky

Heat
  • Heat close to the Sun the temperature was too high for light elements to be solid.
Heating effect
  • Heating effect the hot early Sun pushed gases further out than the solid matter.
Materials
  • Materials only substances with high melting points, such as iron and rock, could form solids there.
Size
  • Size the nebula held only a small proportion of heavy elements, so these planets stayed small.
Result
  • Mercury, Venus, Earth and Mars are small and rocky.

Part 6 of 9Why the outer planets are gaseous

Cold
  • Cold the temperature was low enough for light substances to exist as solids or be held, such as hydrogen, helium, water and methane.
Growth
  • Growth plenty of material was available, so the planets became exceptionally large.
Result
  • Jupiter, Saturn, Uranus and Neptune are large and gaseous, mostly hydrogen and helium.

Part 7 of 9Leftover material and evidence

Leftovers
  • Leftovers rocky debris forms asteroids, which stay in the belt between Mars and Jupiter because of Jupiter's strong gravity.
  • Icy leftovers became comets.
Same plane
  • Same plane all the planets orbit in the same direction in nearly the same plane, as expected from one spinning disc.
Dating
  • Dating radioactive dating of meteorites and Moon rocks gives ages of about 4.5 to 4.6 billion years.

Part 8 of 9Sequence of formation

1
A cloud of gas and dust (nebula) is disturbed.
2
Gravity pulls it together and it spins faster and flattens into an accretion disc.
3
The centre becomes very hot and dense as a protostar.
4
Nuclear fusion of hydrogen starts and the Sun becomes stable.
5
Smaller lumps accrete into planets, with rocky planets near the Sun and gas giants far out.
6
Leftover debris forms asteroids, comets and moons.

Part 9 of 9More from the specification

More from the specification
Formation of the Solar System from a Nebula
  • The Solar System formed approximately 4.6 billion years ago when a giant interstellar cloud of gas and dust collapsed under its own gravitational attraction;
    • conservation of angular momentum caused the collapsing nebula to spin faster and flatten into an accretion disk.
Planetary Orbits and Gravitational Field Strength
  • Planets revolve around the Sun in slightly elliptical orbits governed by the Sun's gravitational field strength;
    • orbital speed v = 2π·r / T is highest for planets with smaller orbital radius r,
  • as gravitational attraction is strongest closer to the Sun.
Planetary Rotation and Daylight Hours
  • A planet rotates on its tilted axis as it orbits the Sun;
    • Earth's 24-hour axial rotation produces the day-night cycle,
  • while its axial tilt causes seasonal variations in daylight hours between the northern and southern hemisphere.
Kinetic energy
  • K = ½mv2, energy of motion.
Artificial satellite
  • A man-made object orbiting a body in space.
Distance
  • Total length of path travelled, a scalar.
Hemisphere
  • Half of the Earth, northern or southern.
Radius
  • Distance from the centre to the circular path.
Period
  • Time for one revolution.
Gravitational field
  • Region where mass experiences gravitational force.
Orbital speed
  • Speed of an orbiting object, √(GM/r).
Field strength
  • G = Fg/m.
Elliptical orbit
  • Orbit with constant E and L but varying speed.

Key terms

TermMeaning
NebulaA cloud of gas and dust in space.
ProtostarA hot, dense ball of gas before nuclear fusion starts.
AccretionGrowth of larger bodies by smaller particles joining under gravity.
Accretion discA rotating disc of material around a forming star in which planets grow.
Nuclear fusionJoining of light nuclei to make heavier ones, releasing energy.
Gas giantA large planet made mainly of hydrogen and helium.

Avoid these mistakes

1
Planets were thrown out of the Sun — they formed from the same cloud at the same time as the Sun.
2
The Sun burns like a fire — it releases energy by nuclear fusion.
3
Fusion started as soon as the cloud began to collapse — it needed the core to reach about 10 million °C.
4
Gas giants are far out because they are heavy — they are far out because it was cold enough there for them to collect gas and ice.

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