Understanding the Solar System

KS3 Physics: Space Physics

Interactive 3D View

Explore the planetary orbits. Click and drag to rotate, scroll to zoom. Note: Sizes and distances are not to scale for visibility.

Our Place in Space

The Solar System is a gravitationally bound system comprising the Sun and the objects that orbit it. It formed approximately 4.6 billion years ago from the gravitational collapse of a giant interstellar molecular cloud. The vast majority of the system's mass is in the Sun, with the majority of the remaining mass contained in Jupiter.

The Sun

The Solar Engine Star: Type G2V

The Sun is a main-sequence star, and it is the heart of our solar system. Gravity holds the Solar System together, keeping everything from the biggest planets to the smallest particles of debris in its orbit. The connection and interactions between the Sun and Earth drive the seasons, ocean currents, weather, climate, radiation belts and auroras.

Nuclear Fusion

Deep inside the Sun's core, the pressure and temperature are so intense (about 15 million degrees Celsius) that hydrogen atoms are smashed together to form helium. This process, known as nuclear fusion, releases colossal amounts of energy, which radiates outward as heat and light.

The Inner System: Terrestrial Planets

1. Mercury

The smallest planet and closest to the Sun. It has no atmosphere to retain heat, leading to extreme temperature fluctuations.

  • Structure: Large iron core, rocky mantle.
  • Day Length: 59 Earth days.
  • Year Length: 88 Earth days.

2. Venus

Similar in structure to Earth but with a toxic atmosphere consisting mainly of carbon dioxide with clouds of sulphuric acid.

  • Feature: Hottest planet due to the Greenhouse Effect.
  • Rotation: Spins retrograde (backwards) slowly.

3. Earth

Our home. The only planet known to harbour life, situated in the "Goldilocks Zone" where liquid water can exist.

  • Atmosphere: 78% Nitrogen, 21% Oxygen.
  • Satellite: One natural satellite, The Moon.

4. Mars

The Red Planet, coloured by iron oxide (rust) on its surface. It has the largest volcano in the solar system, Olympus Mons.

  • Potential for Life: Evidence suggests ancient liquid water.
  • Moons: Phobos and Deimos.

The Asteroid Belt

Located between Mars and Jupiter, this region contains millions of rocky bodies. Despite popular cinema depicting it as crowded fields of rock, the average distance between objects is approximately 600,000 miles. It contains the dwarf planet Ceres.

"Asteroids are leftovers from the formation of our solar system about 4.6 billion years ago."

The Outer System: Gas & Ice Giants

5. Jupiter

The King of Planets. A gas giant with a mass more than two and a half times that of all the other planets combined.

Famous Feature: The Great Red Spot, a storm that has raged for centuries.

6. Saturn

Famous for its spectacular ring system, made of ice chunks and rock. It is the least dense planet; it would float in water!

Moons: Has 83 confirmed moons, including Titan.

7. Uranus

An ice giant. It is unique because it rotates on its side, rolling around the Sun like a ball.

Temp: The coldest planetary atmosphere, roughly -224°C.

8. Neptune

Windy and cold. Neptune was the first planet located through mathematical calculations rather than telescopic observation.

Winds: Supersonic winds reaching 1,200 mph.

How Gravity Rules the System

Gravity is the unseen force that dominates the universe. In our solar system, the Sun's immense mass warps the space around it, creating a "well" that planets fall into. However, because the planets are moving sideways at great speed, they miss the Sun and continue to circle it. This is called an orbit.

Planetary orbits are not perfect circles; they are ellipses (slightly oval-shaped). The closer a planet is to the Sun, the stronger the gravitational pull, and the faster it must travel to stay in orbit.

Mathematical Relationships

The gravitational force ($F$) between two objects depends on their masses ($m_1, m_2$) and the distance ($r$) between them:

F = G × (m₁ × m₂) / r²

Where G is the gravitational constant. This explains why your weight is different on other planets—the mass of the planet determines the gravitational field strength (g).