The Solar System (CIE IGCSE Physics)

• 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 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 divided into two groups
  • the inner rocky planets
  • the outer 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 satellites: 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 and 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 which occupy the inner Solar System

• 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 which occupy the outer Solar System

Orbiting bodies

• The Solar System is made up of many bodies which orbit around other bodies
• Smaller bodies orbit around larger bodies
  • For example, planets orbit the Sun and moons orbit planets

• The orbiting bodies in the Solar System are shown in the table below:

Table of orbiting bodies in the Solar System

orbiting body	body it orbits
planet	the Sun
moon	planet
comet	the Sun
asteroid	the Sun
artificial satellites	the Earth

 

Extended tier only

• 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 (relative to Earth)	Orbital period (Earth years)	Mean surface temperature (°C)	Density (kg/m3)	Diameter (103 km)	Mass (relative to Earth)	Surface gravity (N/kg)	Number of moons
Mercury	0.39	0.24	350	5429	4.9	0.06	3.7	0
Venus	0.72	0.60	460	5243	12.1	0.82	8.9	0
Earth	1	1	20	5514	12.8	1	9.8	1
Mars	1.5	2	−23	3934	6.8	0.11	3.7	2
Jupiter	5.2	12	−120	1326	143	320	23.1	63
Saturn	9.6	30	−180	687	121	95	9.0	61
Uranus	19	84	−210	1270	51	15	8.7	27
Neptune	30	160	−220	1638	50	17	11.0	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