Solar System Planets Science Grade 3 | Orchids International Schools
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The Solar System

Concept: Planets

  • A group of celestial bodies which revolve around the Sun forms the solar system.
  • The solar system is a part of the universe.
  • The universe means everything. It includes the whole of space, matter and energy. The Earth and the Moon are part of the universe, along with the Sun and the other planets.

Solar system:

  • Our Solar system is a part of a bigger celestial system called the Milky Way galaxy.
  • A galaxy is a massive assemblage of hundreds of billions of stars and different heavenly bodies.
  • The solar system consists of mainly eight planets, dwarf planets and their moons.
  • The Sun is located at the centre of the solar system. Planets surround the Sun and keep on revolving around it. Moons surround the planets and revolve around them.
  • The eight planets are— Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.
  • Out of these, Mercury, Venus, Earth and Mars are made of solid things with a molten centre. These are called inner planets.
  • Jupiter, Saturn, Uranus and Neptune are called outer planets. Beyond the orbit of Neptune, there are many dwarf planets.


As per the Scientific Union of Astronomers, an object is said to be a planet if—

  1. It orbits around the star.
  2. It is big enough to look like a sphere.
  3. It has a specific orbit that is not occupied by any other heavenly body.

Differences between the inner and outer planets:

Inner planets Outer planets
Orbits are short. Orbits are long.
They spin slowly. They spin faster.
Do not have rings around them. Have ring-like structures around them.
Have very few moons. Have many moons.
Made of rocks, metals, etc. Made of gases and liquids.
  1. Mercury:
    • It is the smallest planet in the solar system and is also the closest to the Sun.
    • It does not have an atmosphere. So, the days are very hot and the nights are equally cold.
    • Mercury’s one year is of 88 Earth days.
    • It does not have any moon.
  2. Venus:
    • It is the second planet from the Sun.
    • Its size is similar to that of the Earth.
    • However, it is surrounded by a toxic and thick atmosphere of carbon dioxide. Therefore, it is the hottest planet in the solar system.
    • 225 Earth days make one year on Venus.
    • It has no moons.
  3. Earth:
    • It is the only known planet in the solar system with the presence of liquid water and life on it.
    • The Earth’s atmosphere is formed of a mixture of many gases suitable for the survival of life. This atmosphere shields the Earth from the harmful sun rays.
    • 365 days make 1 year on Earth.
    • It has one moon.
  4. Mars:
    • It is the fourth planet from the Sun.
    • It has a deserted, cold surface with a very thin atmosphere around it.
    • 687 Earth days make 1 year on Mars.
    • It has 2 moons. Mars is the only inner planet to have moons.
  5. Jupiter:
    • It is the fifth planet from the Sun and the first outer planet.
    • It is a gas giant and has faded dust rings around it.
    • Jupiter is the largest planet in the solar system.
    • 4333 Earth days make 1 year on Jupiter.
    • It has 79 moons.
  6. Saturn:
    • It is the 6th planet from the Sun.
    • It has a system of rings around it. Galileo observed these in 1610 for the first time.
    • Around 10,585 Earth days make one year on Saturn.
    • It has the highest number of moons, i.e., 82.
  7. Uranus:
    • It is the 7th planet from the Sun and also the third biggest planet.
    • Uranus has 13 known narrow rings around it.
    • The bright blue colour of the planet is because of the presence of methane in its atmosphere.
    • Around 30660 Earth days make 1 year on Uranus.
    • It has 27 moons.
  8. Neptune:
    • It is the 8th planet from the Sun.
    • It is an icy, dark blue giant planet of our solar system.
    • Neptune is surrounded by rings made of dust and debris.
    • Around 16,225 Earth days make 1 year on Neptune.
    • Neptune has 14 known moons.

Dwarf planet—Pluto

  • Pluto was a part of our solar system before 2006.
  • However, in 2006 it was categorised as a dwarf planet due to its size and the presence of other objects in its orbit.
  • Pluto’s orbit differs from the rest of the planets; it is inclined and has an oval shape.
  • It is situated in the Kuiper belt region.
  • Around 90,520 Earth days make 1 year on Pluto.
  • Pluto has 5 moons, the largest one called Charon.

New Words:

Telescope: A device used to observe celestial bodies as it makes these distant objects appear nearer.

Atmosphere: A layer of a mixture of gases surrounding a planet.

Astronomer: One who studies the universe, stars, and celestial bodies as a whole.

Celestial objects: These are naturally occurring objects in space that can be observed by particular devices.

Did You Know?

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