The solar system

The Solar System is a vast and complex system of planets, moons, and other celestial bodies, all held together by the gravitational pull of the Sun. In this section, we will explore the structure of the Solar System, the accretion model of its formation, and the fundamental role of gravity in shaping it.

The solar system

The Solar System is made up of many different components, each playing a role in the overall structure and function of the system:

• (a) The Sun: The Sun is the central star of the Solar System, and its gravitational pull keeps all other bodies in orbit around it.

• (b) The Eight Named Planets:

  • There are eight planets in the Solar System: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.

  • These planets are arranged in order of increasing distance from the Sun. The first four (Mercury to Mars) are called terrestrial planets, and the next four (Jupiter to Neptune) are called gas giants or ice giants.

• (c) Minor Planets and Asteroids:

  • The Solar System also contains minor planets or dwarf planets, such as Pluto, and countless asteroids, which are mostly found in the asteroid belt between Mars and Jupiter.

• (d) Moons:

  • Many planets have moons that orbit around them. For example, Earth has one moon, while Jupiter has dozens.

• (e) Smaller Solar System Bodies:

  • Other objects include comets (balls of ice and dust that develop tails as they approach the Sun) and natural satellites (including moons and smaller orbiting bodies).

The eight planets in the solar system (from left to right, Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune)

Formation of the solar system

The Solar System formed about 4.6 billion years ago from a cloud of gas and dust. The accretion model helps explain how the planets and other bodies formed:

• (a) Dependence on Gravity:

  • The force of gravity caused the interstellar cloud to collapse into a rotating disc. This gravitational collapse caused the formation of the Sun at the center.

• (b) Presence of Elements:

  • The cloud of gas and dust contained a mix of elements. Lighter gases like hydrogen and helium accumulated in the outer regions, forming the gas giants, while heavier elements closer to the center formed the rocky terrestrial planets.

• (c) Rotation and Accretion Disc:

  • As the cloud collapsed, it began to rotate, and particles in the cloud clumped together through a process called accretion. Over millions of years, these clumps formed planets and other celestial bodies.

• Differences Between Planets:

  • The four inner planets (Mercury, Venus, Earth, Mars) are small and rocky because the high temperatures near the Sun prevented gases from condensing.

  • The four outer planets (Jupiter, Saturn, Uranus, Neptune) are large and gaseous, containing a lot of hydrogen and helium, which condensed in the cooler outer regions.

Gravitational fields

Gravity is a fundamental force that shapes the Solar System:

• (a) Strength of the Gravitational Field:

  • The gravitational field strength at the surface of a planet depends on the mass of the planet. Larger planets with more mass have a stronger gravitational pull.

  • Gravity decreases as the distance from the planet increases.

• (b) Effect of Mass and Distance:

  • Gravity decreases with distance. This is why astronauts on the International Space Station experience microgravity—they are far enough from Earth's center that gravity is weaker.

Speed of light and distances from the solar system

Light travels at a speed of 300,000 km/s. We can use this speed to calculate how long it takes for light to travel between objects in the Solar System.

For example:

• Light from the Sun takes about 8 minutes to reach Earth.

• This helps us understand the vast distances between celestial bodies in space.

The sun as the centre of the solar system

• The Sun contains most of the mass of the Solar System—over 99%. This immense mass creates a strong gravitational pull that keeps all the planets and other bodies in orbit around the Sun.

• The planets are kept in orbit by the balance between the gravitational pull of the Sun and their own orbital speed.

Gravitational attraction and orbits