The Solar System (CIE IGCSE Physics)

• The Solar System consists of:
  1. The Sun
  2. Eight planets
  3. Natural and artificial satellites
  4. Dwarf planets
  5. Asteroids and comets

The Sun & the Planets

• The Sun lies at the centre of the Solar System
  • The Sun is a star that makes up over 99% of the mass of the solar system

• There are eight planets and an unknown number of dwarf planets which orbit the Sun
  • The gravitational field around planets is strong enough to have pulled in all nearby objects with the exception of natural satellites
  • The gravitational field around a dwarf planet is not strong enough to have pulled in nearby objects

• The 8 planets in our Solar System in ascending order of the distance from the Sun are:
  • Mercury
  • Venus
  • Earth
  • Mars
  • Jupiter
  • Saturn
  • Uranus
  • Neptune

Satellites

• There are two types of satellite:
  • Natural
  • Artificial

• Some planets have moons which orbit them
  • Moons are an example of natural satellites

• Artificial satellites are man-made and can orbit any object in space
  • The International Space Station (ISS) orbits the Earth and is an example of an artificial satellite

Asteroids & Comets

• Asteroids and comets also orbit the sun
• An asteroid is a small rocky object which orbits the Sun
  • The asteroid belt lies between Mars and Jupiter

• Comets are made of dust and ice and orbit the Sun in a different orbit to those of planets
  • The ice melts when the comet approaches the Sun and forms the comet’s tail

The objects in our solar system

• There are 4 rocky and small planets: Mercury, Venus, Earth and Mars
  • These are the nearest to the Sun
• There are 4 gaseous and large planets: Jupiter, Saturn, Uranus and Neptune
  • There are the furthest from the sun

The eight planets of our Solar System

• The differences in the types of planets are defined by the accretion model for Solar System formation

• The Sun was thought to have formed when gravitational attraction pulled together clouds of hydrogen dust and gas (called nebulae)
• The Solar System then formed around 4.5 billion years ago
  • The planets were formed from the remnants of the disc cloud of matter left over from the nebula that formed the Sun
  • These interstellar clouds of gas and dust included many elements that were created during the final stages of a star's lifecycle (a previous supernova)
• Gravity collapsed the matter from the nebula in on itself causing it to spin around the Sun
  • The gravitational attraction between all the small particles caused them to join together and grow in an accretion process
• A rotating accretion disc is formed when the planets emerged

The accretion model of the creation of the Solar System

• As the Sun grew in size it became hotter
• Where the inner planets were forming near the Sun, the temperature was too high for molecules such as Hydrogen, Helium, water and Methane to exist in a solid state
  • Therefore, the inner planets are made of materials with high melting temperatures such as metals (e.g. iron)
  • Only 1% of the original nebula is composed of heavy elements, so the inner, rocky planets could not grow much and stayed as a small size, solid and rocky
• The cooler regions were further away from the Sun, and temperature was low enough for the light molecules to exist in a solid state
  • The outer planets therefore could grow to a large size up and include even the lightest element, Hydrogen 
  • These planets are large, gaseous and cold