The Solar System - CCEA

• The structure of the Solar System.

• The order of the planets.

• Natural and artificialsatellites.

The Earth is our planet.

It is one of eight planets that move around the sun, each in an oval shaped,elliptical orbit.

Our Moon orbits the Earth.

All of the other planets except Mercury and Venus have at least one moon.

Comets and asteroids also orbit the Sun.

Together the Sun, the eight planets, the moons, asteroids and comets make up our Solar System.

Key point

The main features of our Solar System are:

• The Sun.

• The eight planets.

• Moons.

• Asteroids.

• Comets.

The Sun is the largest object in the Solar System and was the first to form.

The huge gravitational pull of the Sun keeps many other objects - planets, dwarf planets, asteroids and comets - in orbit around it.

The Sun alone contains 99.8% of the total mass in the Solar System.

Planets

The Earth is one of eight planets in the Solar System.

The planets orbit the Sun at different distances.

The following sentence may help with remembering the order of the names of the planets from the Sun outwards:

My Very Easy Method Just Speeds Up Naming

1. Mercury
2. Venus
3. Earth
4. Mars
5. Jupiter
6. Saturn
7. Uranus
8. Neptune

The different planets have different properties and conditions.

In general, as the distance from the Sun increases:

• The temperature decreases, for example, Mercury is 430 °C whereas Neptune is -200 °C.

• The time taken to orbit the Sun increases, for example, Mercury orbits once every 88 Earth days, but Neptune orbits once every 165 Earth years.

What are the different planet groups?

Astronomers have divided the planets into two groups of four:

• The four inner planets (Mercury, Venus, Earth and Mars), which are small, rocky, dense planets, close to the Sun, therefore they are generally warmer.

• The four outer planets (Jupiter, Saturn, Uranus and Neptune), which are large balls of gas, far from the Sun, therefore they are generally colder. They are called the gas giants.

When the Solar System formed, rocks (and other dense, heavy materials in the dust cloud such as iron and uranium) tended to gather closer to the Sun, and these materials combined together to form the inner planets.

Lighter gaseous substances gathered together further away from the Sun and formed the outer gas giants.

For a planet to form, its own gravity must be strong enough to make it round or spherical in shape.

Its gravitational field must also be strong enough to ‘clear the neighbourhood’, pulling smaller nearby objects into its orbit.

The Moon

A body orbiting a planet is called a satellite.

The Moon is the only natural satellite that orbits planet Earth.

Many planets have moons, and some planets have many moons - Saturn has more than 50.

Dwarf planets

Pluto is a dwarf planet.

The gravitational field of a dwarf planet is not strong enough to 'clear the neighbourhood', so there may be other objects in its orbit around the Sun.

The Solar System contains hundreds of dwarf planets, including Ceres (the only dwarf planet in the asteroid belt).

Asteroids

Asteroids are made of metals and rocky material.

There are many asteroids in our Solar System which orbit the Sun in oval or egg-shaped elliptical orbits which can take millions of years to complete.

There are large numbers of asteroids orbiting the Sun in the asteroid belt between Mars and Jupiter.

There are also many in a region beyond Neptune called the Kuiper Belt.

Comets

The Solar System also contains objects called comets.

Comets are similar to asteroids, but are made of ice, dust and rocky material.

As a comet approaches the Sun, it begins to vaporise, which means that it turns into a gas. It then produces a distinctive tail.

The main difference between asteroids and comets is their composition, as in, what they are made of.

• Asteroids are made up of metals and rocky material.

• Comets are made up of ice, dust and rocky material.

• Both asteroids and comets were formed early in the history of the Solar System about 4.5 billion years ago.

Gravity is the force needed to maintain the orbit of planets, asteroids and comets around a star and moons and artificial satellites around a planet.

An artificial satellite is a man-made body placed in orbit round the Earth or another planet in order to collect information about it or for communication purposes.

The International Space Station is an example of an artificial satellite.

Key Point

Artificial satellites can be used for:

• Communications – satellite television and phone calls.

• Earth observation - including weather forecasting, tracking storms and pollution, spying and satellite photography.

• Navigation - including the Global Positioning System (GPS).

• Astronomy – looking into outer space from our Solar System.