• The solar system constitutes a collection of heavenly bodies that revolve around the Sun. It includes:
    (i) The Sun
    (ii) The Eight Planets and their satellites
    (iii) Asteroids
    (iv) Meteors
    (v) Comets
    (vi) Drifting particles 

The Sun 

  • One of more than 100 billion stars of the Milky Way. 
  • Accounts for 99.85 per cent mass of the solar system.

Planetary World 

  • Under the impact of the Sun's gravitational force, all the eight planets revolve around the Sun, in an elliptical orbit. The planets, in order from the Sun, are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. 
  • The planets, except Venus and Uranus, rotate anti-clockwise at their axes. 
  • The planets on the basis of their characteristics may be classified into: (i) Terrestrial (earth-like) planets or inner planets which have denser ma-terial. Planets in this category are Mercury, Venus, Earth, and Mars. (ii) Jovian planets (Jupiter-like) or outer planets which are gaseous, gigantic with large satellite families and high rotational velocities. These are Jupiter, Saturn, Uranus, and Neptune. 
  • The largest terrestrial planet is Earth while the smallest jovian planet is Neptune. 
  • The planets in the descending order of their sizes are: Jupiter, Saturn, Uranus, Neptune, Earth, Venus, Mars, Mercury. 9 Planets Mercury and Venus have no satellite. 
  • Planet closest to the Earth is Venus. After that come Mars, Mercury, and Jupiter.


  • Mercury, the innermost planet, has the fastest orbital motion (48km/s) and the shortest period of revolution, i.e. 88 days. 
  • This fast speed keeps it from being drawn into the Sun's gravitational field. 
  • The planet is characterized by the maximum diurnal range of temperature. 

Venus (The Veiled Planet) 

  • Venus is the closest planet to the Earth. It is also called Earth's twin because of its similar size, density, and mass. 
  • The planet is considered as the hottest planet in the solar system. It has the slowest rotational velocity.

Earth (The Blue Planet) 

  • The earth is the fifth largest planet of the solar system. It is the densest planet of the solar system. 
  • It has such temperature ranges that water can exist here in solid, liquid, and gaseous forms. This feature has made possible the existence of life forms on this planet. 

Mars (The Red Planet) 

  • The angle of inclination and period of rotation of Mars is nearly the same as that of Earth. Hence Mars has seasons much like the Earth.
  • There is evidence on the surface of Mars of not only stream action, but of catastrophic flooding too. Recently, the Europian Union's space missions Beagle-2 and NASA's Spirit were undertaken for the exploration of Mars. 

Jupiter (The Giant Planet) 

  • Jupiter is composed mostly of gas and liquid swirling in complex pat-terns. 
  • It has the fastest rotational velocity among planets. 
  • Its satellites are, however, solid bodies. The four largest of its sixteen known satellites are: Lo, Europa, Ganemede, and Callisto which are called Galilean satellites. Ganemede is the largest satellite of the solar system. 

Saturn (The Ringed Planet) 

  • Saturn has a spectacular system of seven rings (discovered by Galileo), identified by the letter 'A' to `G' (though not in alphabetical order) the rings are made up of individual moonlets of varing sizes. 
  • Saturn has the largest number of satellites; a total of eighteen or more. Titan, the largest satellite, is the only one in the solar system with an atmosphere of its own. 

Uranus (The Green Planet or The Methane Planet) 

  • Its rotational motion has the appearance of rolling, unlike other planets which spin on their axis. 
  • Uranus has coldest atmosphere in the solar system.


  • Uranus and Neptune can be considered twins because of similar size, colour (pale-greenish), attributable to the methane in their atmospheres. 
  • Neptune's atmosphere contains an earth-sized blemish called the Great Dark Spot. 
  • Neptune has eight tiny satellites. Triton is the largest satellite.