2. UNIT-2 SOLAR SYSTEM
The Solar System is made up of the Sun and all objects that move around it because of gravity. These include planets, moons, asteroids, comets, and dwarf planets.
The Solar System formed about 4.6 billion years ago from a cloud of gas and dust. The Sun contains most of the mass of the Solar System. The planets revolve around the Sun in nearly circular paths called orbits.
Let us now move forward and explore our dynamic planet in greater detail.
1. OBJECTIVES
After studying this unit, you should be able to:
Ø Describe the structure and components of the solar system
Ø Explain the formation and evolution of the solar system
Ø Identify planets and their characteristics
Ø Understand the role of the Sun in the solar system
2. STRUCTURE AND COMPOSITION
The Solar System consists of the Sun, planets, moons, asteroids, comets, and other small bodies. The Sun is at the center and contains about 99.86% of the total mass of the Solar System.
The planets revolve around the Sun in almost circular paths called orbits and lie mostly in a flat plane known as the ecliptic plane. The Solar System is divided into:
Inner Solar System – includes the four rocky planets and the asteroid belt.
Outer Solar System – includes giant planets and icy objects beyond Neptune.
Inner planets are mainly made of rock and metals, while outer planets contain gases and ices. The distribution of materials depends on distance from the Sun and temperature conditions.
3. DISTANCES AND SCALES
Distances in the Solar System are very large, so astronomers use the unit called Astronomical Unit (AU).
1 AU = average distance between Earth and the Sun = 150 million km.
Inner planets are closer to the Sun and move faster.
Outer planets are farther away and take more time to complete one revolution.
Example:
1) Mercury is closest to the Sun.
2) Neptune is about 30 AU away from the Sun.
3) As distance from the Sun increases, the space between planetary orbits also increases.
Sun
The Sun is a star and the main source of energy in the Solar System. It controls the movement of all planets through its gravity.
Key points:
· Composed mainly of hydrogen and helium.
· Produces energy through nuclear fusion, where hydrogen changes into helium.
· Releases heat and light as electromagnetic radiation.
· Provides light, warmth, and energy necessary for life on Earth.
· The large mass of the Sun makes it the dominant body of the Solar System.
PLANETS
There are eight major planets in the Solar System.
Inner (Terrestrial) Planets
· Mercury – smallest and closest planet.
· Venus – hottest planet with thick atmosphere.
· Earth – only planet known to support life.
· Mars – red planet with thin atmosphere.
These planets are rocky, smaller in size, and have few or no moons.
Outer (Giant) Planets
· Jupiter – largest planet; gas giant.
· Saturn – famous for its rings.
· Uranus – ice giant that rotates on its side.
· Neptune – farthest planet with strong winds.
Outer planets are larger and mainly made of gases and ices.
Pluto (Dwarf Planet)
Pluto is now classified as a dwarf planet located beyond Neptune. Pluto was once considered the ninth planet of the Solar System but is now classified as a dwarf planet. It is located in the Kuiper Belt beyond Neptune. Pluto is small, icy, and follows an elliptical orbit around the Sun. It has a large moon called Charon, and together they form a unique planetary system.
PLANETS:
(Quick Memory Trick for Order of Planets)
(M V E M J S U N)
My Very Easy Method Just Shows Us Names
(Source; The image was generated by an AI model (DALL·E by OpenAI))
SUMMARY
The Solar System formed about 4.6 billion years ago and consists of the Sun at the center and planets orbiting around it. The Sun contains most of the system’s mass and supplies energy through nuclear fusion. Planets are divided into inner rocky planets and outer giant planets. Distances are measured using the Astronomical Unit (AU). Earth is the only known planet supporting life. The Solar System also contains moons, asteroids, comets, and dwarf planets such as Pluto. Understanding the Solar System helps us learn about Earth’s origin and its place in space.