6.1.2 The Solar System

Learning Objectives

Core

1. Describe the Solar System as containing:

1. one star, the Sun
2. the eight named planets and know their order from the Sun
3. minor planets that orbit the Sun, including dwarf planets such as Pluto and asteroids in the asteroid belt
4. moons, that orbit the planets
5. smaller Solar System bodies, including comets and natural satellites of phases

2. Know that, in comparison to each other, the four planets nearest the Sun are rocky and small and the four planets furthest from the Sun are gaseous and large, and explain this difference by referring to an accretion model for Solar System formation, to include:

1.  the model’s dependence on gravity
2.  the presence of many elements in interstellar clouds of gas and dust
3.  the rotation of material in the cloud and the formation of an accretion disc

3. Know that the strength of the gravitational field

1.  at the surface of a planet depends on the mass of the planet
2.  around a planet decreases as the distance from the planet increases

4. Calculate the time it takes light to travel a significant distance such as between objects in the Solar System

5. Know that the Sun contains most of the mass of the Solar System and this explains why the planets orbit the Sun

6. Know that the force that keeps an object in orbit around the Sun is the gravitational attraction of the Sun

Supplement

7. Know that planets, minor planets and comets have elliptical orbits, and recall that the Sun is not at the centre of the elliptical orbit, except when the orbit is approximately circular

8. Analyze and interpret planetary data about orbital distance, orbital duration, density, surface temperature and uniform gravitational field strength at the planet’s surface

9. Know that the strength of the Sun’s gravitational field decreases and that the orbital speeds of the planets decrease as the distance from the Sun increases

10. Know that an object in an elliptical orbit travels faster when closer to the Sun and explain this using the conservation of energy

Contents to learn

The Solar System

   Our solar system consists of

• One star (Sun)
• Eight planets
• Asteroids
• Natural and artificial satellites
• Dwarf planets
• Comets

The Sun

• The Sun is the central star of our Solar System, around which all the planets, dwarf planets, asteroids and other objects orbit.
• The mass of the entire Solar System is mostly dominated by the Sun it contains more than 99.8% of the total mass of the Solar System.

Eight Planets

Inner Planets

They are smaller, solid, rocky, have a layered structure, and have high densities.

• Mercury
• Venus
• Earth
• Mars

Outer Planets

They are large, colder, have low densities, and are mostly made up of gases.

• Jupiter
• Saturn
• Uranus
• Neptune

Asteroids

• The asteroid belt is in space between Mars and Jupiter.
• There are millions of asteroids orbiting the Sun.
• Asteroids are made up of rocks and metallic objects that orbit the sun.

Natural and Artificial Satellites

Natural Satellites

• Moons are natural satellites that revolve around planets.
• Most planets in the Solar System have at least one moon and some planets have a large number of moons.

Artificial Satellites

• An artificial satellite is a human-made object that is intentionally placed into orbit around the Earth or Moon or another planet.
• Examples of artificial satellites include communication satellites, weather satellites, navigation satellites, the Hubble Space Telescope and the International Space Station(ISS).

Dwarf planets

• Dwarf planets orbit the Sun and are located in various regions of the Solar System.
• Dwarf planets share characteristics of both planets and smaller Solar System objects, such as asteroids and comets.

Comets

• Comets are composed of ice, dust, rock, and organic compounds that orbit the Sun.
• Comets nucleus is made up mostly of ice and when they approach the Sun the ice melts due to solar radiation and solar wind forming a tail.
• The tail of a comet is created as a result of this melting process.

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