NCERT Summary: Our Solar System - 1 | Geography for UPSC CSE PDF Download

The Solar System

Formation (The Nebula)

•  The solar system began as a nebula, a vast cloud of gas and dust in space. 
•  This nebula started to collapse under its own gravity, leading to the formation of the Sun at its core and the surrounding material that would become the planets. 
•  This process is believed to have occurred around 5-5.6 billion years ago, with the planets forming later, about 4.6 billion years ago. 

The Sun

• The Sun is a large sphere of hot gases, primarily composed of Hydrogen.
• The bright surface of the Sun is known as the Photosphere.
• The outermost layer of the Sun’s atmosphere, which consists of thin and hot gases, is referred to as the Corona.
• The Corona can only be seen during a total solar eclipse.
  

Planets

The solar system is a vast and complex system that includes the Sun and all the celestial bodies that are bound to it by gravity. This includes planets, moons, asteroids, comets, and a variety of smaller objects. Around the sun, there are eight planets (Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune), their satellites, asteroids, comets, meteoroids, and interplanetary dust. Pluto, once a part of the Solar System, is now classified as a dwarf planet. 

These planets are further categorized into two groups:
Inner Planets: Also known as terrestrial planets, they are composed mainly of rock and metal. They have solid surfaces and are denser than the outer planets. The inner planets are:

• Mercury: The closest planet to the Sun, Mercury has a thin atmosphere and is known for its extreme temperature fluctuations.
• Venus: Often called Earth’s twin due to its similar size, Venus has a thick, toxic atmosphere and is the hottest planet in the solar system.
• Earth: The only planet known to support life, Earth has a diverse range of environments and a protective atmosphere.
• Mars: Known as the Red Planet, Mars has a thin atmosphere and is home to the largest volcano and canyon in the solar system.

Outer Planets: These planets are much larger than the inner planets and are primarily composed of gases. They have thick atmospheres and lack solid surfaces. The outer planets are:

• Jupiter: The largest planet in the solar system, Jupiter is known for its Great Red Spot, a massive storm, and its many moons.
• Saturn: Famous for its stunning rings, Saturn is the second-largest planet and is made mostly of hydrogen and helium.
• Uranus: An ice giant with a unique tilt, Uranus has a blue color due to methane in its atmosphere.
• Neptune: The farthest planet from the Sun, Neptune is known for its deep blue color and strong winds.

Components

• Asteroids: These are small, rocky bodies that orbit the Sun, primarily found in the asteroid belt between Mars and Jupiter. They vary in size and shape and are remnants from the early solar system.
• Comets: Comets are composed of ice, dust, and rocky material. They originate from the outer regions of the solar system and, when they approach the Sun, the heat causes their ice to vaporize, creating a glowing coma and tail.Meteors: 
  • Meteors are small space objects, which can include tiny pieces of comets or fragments of asteroids. 
  •  When these objects enter the Earth's atmosphere, they burn up and create a bright streak of light. 
  •  This bright light is often called a shooting star. 
  •  If a meteor is large enough to survive its journey through the atmosphere and lands on Earth, it is referred to as a meteorite. 
  •  It is interesting to note that the number of meteorites found on the Moon is much higher than those on Earth. 
  •  This is because the Moon does not have an atmosphere to burn up these meteors. 

Two Groups of Planets: Terrestrial VS Jovian

Terrestrial Planets (Earth- like)

• Includes Mercury, Venus, Earth, and Mars.
• They have solid, rocky surfaces similar to Earth.
• None of them have rings, though Earth has belts of trapped radiation.
• Only Earth has a strong global magnetic field. Mars and the Moon have localized magnetic fields, but no global field.
  • Mercury: Almost no atmosphere; extremely hot surface, but water ice exists in permanently shadowed polar craters.
  • Venus: Dense, hot, CO₂-rich atmosphere with permanent clouds, hiding the surface.
  • Earth: Supports life with a substantial atmosphere and magnetic field.
  • Mars: Thin CO₂ atmosphere, with polar ice caps of water and carbon dioxide.

Jovian Planets (Jupiter-like / Gas Giants)

• Includes Jupiter, Saturn, Uranus, and Neptune.
• Known as gas giants, they are massive and mainly composed of hydrogen and helium, with traces of other gases and ices.
• All have strong magnetic fields, rings, and numerous satellites.
  • Jupiter: More massive than all other planets combined; emits electromagnetic energy from charged particles in its strong magnetic field.
  • Saturn: Famous for its extensive, complex ring system; visible to the naked eye. Its moon Titan is the second-largest moon in the solar system.
  • Uranus and Neptune: Giant gaseous planets with compositions similar to Jupiter’s.

Galilean Moons of Jupiter:

• Io: Most volcanically active body due to tidal heating.
• Europa: Smooth ice shell; likely has a subsurface liquid water ocean.
• Ganymede: Mountains, valleys, craters, cooled lava flows; ancient surface; possible subsurface ocean.
• Callisto: Heavily cratered, outermost moon; surface unchanged since early formation.

The Moon

The Big Splat

• Scientists have not reached a consensus on earlier theories regarding the Moon's formation. However, the prevailing view is that the Moon became Earth's satellite due to a "giant impact," often referred to as "the big splat."
• This theory suggests that a body measuring between one and three times the size of Mars collided with the Earth shortly after the planet's formation.
• The force of this collision expelled a substantial portion of the Earth's material into space.
• The ejected debris subsequently entered orbit around the Earth and eventually coalesced to form the Moon, approximately 4.44 billion years ago.

Astronomical Units

Light Year

A light year is a measure of distance and not of time. Light travels at a speed of 3,00,000 km/second. Considering this, the distances the light will travel in one year is taken to be one light year. This equals 9.461x10¹² km. The mean distance between the sun and the earth is 149,598,000 km. In terms of light years, it is 8.311 minutes of a year.

Some Interesting Facts about Solar System

Earth Movements & Phenomena