Unit 1: The Earth in the Universe                                            1   2   3   4

2. The Solar System

The Solar system was formed approximately 4,500 million years ago, when a nebula collapsed by gravity.

It is made up of the Sun, eight planets with their satellites, dwarf planets and small bodies called asteroids and comets.

a) The Sun

The Sun is a yellowish medium-sized star. It is made up of hydrogen and helium.

The nuclear reactions taking place in its core produce a huge amount of energy, light and heat.

b) The planets

They are spherical-shaped celestial bodies which revolve around the Sun.

They are divided into two groups:

• The inner planets

They are the four planets closest to the Sun: Mercury, Venus, the Earth and Mars.

They are also known as terrestrial or rocky planets because of their composition and structure.

They have a crust and a mantle of rock and a core of metal. Their atmospheres are very light.

The Earth and Mars have one and two satellites respectively, while Mercury and Venus do not have any.

• The outer planets

They are the four planets farthest from the Sun: Jupiter, Saturn, Uranus and Neptune.

They are also known as gas giants because they have a very thick and dense atmosphere with a small nucleus.

All of them have many satellites.

c) Other celestial bodies

• Satellites

They are rocky bodies which revolve around a planet.

They can be very large or very small and their shape can be spherical or irregular.

• Dwarf planets

        They are small and round rocky bodies which have not cleared

        their orbit around the Sun of other similar bodies.

        Some of them are Pluto, Ceres, Eris, etc.

•  Asteroids

        They are rocky and irregular shaped bodies.

        Their size goes from few meters to hundred kilometers in diameter.

        Some asteroids orbit around the Sun between the orbits of Mars

        and Jupiter and form the Asteroid belt and others orbit

        beyond the orbit of Neptune and form the Kuiper belt.

• Comets

        They are small and irregular bodies which travel around the Sun

        in highly elliptical orbits.

        They are formed in a very far region around the Solar System

        called the Oort cloud.

        They have a nucleus of ice, dust and gas.

        When comets travel close to the Sun, ice starts to evaporate,

        creating a long and bright tail.

2.1. Explain which is the main difference between:

a. the inner and the outer planets

b. asteroids and comets

c. planets and dwarf planets

2.2. Look at the following chart about the main characteristics of

        the planets of the Solar System and answer the questions:

          a. Which planet is the smallest in the Solar System?

          b. Which planet has the least satellites?

          c. Which planet has a horizontal axis?

          d. Which planet is the farthest to the Sun?

          e. Which planet has an atmosphere with oxygen?

          f. Which planet has the lowest surface temperature?

          g. Which planet has the highest surface temperature?

          h. Which planet has the biggest rings?

2.3. Identify the following pictures:

2.4. Listen and say if the following descriptions correspond to the inner

or to the outer planets:

2.5. Taking in account the information provided in activity 2.2,

listen and identify the planet that is been described: