The Solar System (WJEC GCSE Physics: Combined Science)

• The Solar System consists of:
  • The Sun
  • Eight planets
  • Natural and artificial satellites
  • Dwarf planets
  • Asteroids and comets

The Solar System

The Solar System consists of one star (the Sun) and the objects that orbit it, including the planets, moons, dwarf planets, asteroids and comets

The Sun

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

The Sun

The Sun is a star which contains 99% of the mass of the Solar System

The Planets

• There are eight planets which orbit the Sun
• In ascending order of the distance from the Sun, these are:

Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune

• The planets can be categorised into the terrestrial planets and the gas giants

• Terrestrial planets: these are the 4 inner planets (nearest to the Sun):  
  • They are rocky and small
  • They have atmospheres (except for Mercury)

• Gas giants: these are the 4 outer planets (furthest from the Sun):
  
  • They are gaseous and large
  • They are mostly composed of hydrogen and helium gas

The Planets of the Solar System

The eight planets can be split into the four terrestrial planets and the four gas giants

Dwarf Planets

• A dwarf planet is an object similar to a planet, but much smaller
• The gravitational field around a planet is strong enough to pull in nearby objects (with the exception of natural satellites)
• Whereas, the gravitational field around a dwarf planet is not strong enough to pull in nearby objects

Satellites

• There are two types of satellite: natural and artificial

Natural and Artificial Satellites of Earth

The Moon is a natural satellite of the Earth. Many artificial satellites orbit around the Earth.

• Natural satellites are objects that orbit planets
• A moon is a type of natural satellite
• Artificial satellites are manmade objects that orbit another object in space
• The International Space Station (ISS) is an example of an artificial satellite that orbits the Earth 

Asteroids & Comets

• Asteroids and comets also orbit the Sun

Locations of asteroids and comets

Asteroids are found in the Asteroid Belt between Mars and Jupiter, whereas comets are usually found in the outer reaches of the Solar System due to their highly elliptical orbits

• An asteroid is a small rocky object which orbits the Sun
• The asteroid belt lies between Mars and Jupiter

An Asteroid

Asteroids are small, rocky objects

• A comet is an object made of dust and ice which orbits the Sun in a highly elliptical path
• The ice melts when the comet approaches the Sun and forms the comet’s tail

A Comet

Comets are small, icy objects

Comparing Objects in the Solar System

• Over many years, data for the planets, moons and the Sun have been collected
• Some of this data is shown in the table below 

Data for the Planets in the Solar System

Planet	Mean distance from Sun (AU)	Orbital period (Earth years)	Mass (relative to Earth)	Mean temperature (°C)	Number of moons
Mercury	0.39	0.24	0.06	430	0
Venus	0.72	0.60	0.82	480	0
Earth	1	1	1	15	1
Mars	1.5	2	0.11	−63	2
Jupiter	5.2	12	320	−130	63
Saturn	9.6	30	95	−130	61
Uranus	19	84	15	−200	27
Neptune	30	160	17	−200	13

 

• The data allows us to
  • Make comparisons
  • Identify trends and anomalies
  • Make predictions 

• Some examples of comparisons are:
  • Neptune is 30 times further away from the Sun than the Earth
  • Jupiter contains the same mass as 320 Earths

• An example of a trend is:
  • As the distance from the Sun increases, the time it takes to complete one orbit (orbital period) also increases

• An example of an anomaly is:
  • As the distance from the Sun increases, the temperature decreases, except for Venus which has a higher temperature than Mercury

• An example of a prediction is:
  • The temperature of a dwarf planet in the asteroid belt is likely to be around −100°C, but it could be anywhere between −63°C and −130°C as these are the temperatures of Mars and Jupiter