The planets in the solar system are classified into three depending on their proximity with the sun & the structure of the planets. They are as follows:

  1. Inner Planets – Mercury, Venus, Earth & Mars.
  2. Outer Planets – Jupiter, Saturn, Uranus & Neptune.
  3. Dwarf Planets – Pluto, Eris, Haumea & Makemake.
The inner planets are also known as Rocky Planets or Terrestrial Planets whereas outer planets are known as Giant Planets.

Classification of Planets

Inner Planets / Terrestrial Planets

 
Inner Planets

Mercury, Venus, Earth & Mars are included in this category. The main characteristics of Terrestrial Planets are as follows:
  • Rocky structure.
  • Solid surface.
  • High density.
  • Don't possess rings.
  • Relatively small size.
  • Solid rock & metallic core.
  • No or few moons/satellites.

Outer Planets / Jovian Planets

Outer Planets

Jupiter, Saturn, Uranus & Neptune form the Jovian Planets. The word "Jovian" is derived from Jupiter.  The main characteristics of Terrestrial Planets are as follows:
  • No solid surface.
  • Huge size.
  • Possess sings.
  • Low density.
  • Small liquid core.
  • Multiple moons/satellites.
Based on their composition, this category is further divided into two They are:
  1. Gas Giants – Jupiter & Saturn are the Gas Giants. Their main composition consists of Hydrogen and Helium.
  2. Ice Giants – Uranus & Neptune. Ice, rocks, and a mixture of methane, water, and ammonia can be found on these planets.
Until 2006, there were 9 planets. But in the year 2006, the International Astronomical Union (IAU) (naming organization of celestial bodies decided to categorize the ninth planet Pluto as a dwarf planet.

Dwarf Planets

Planets that are smaller in mass and are found in the Kuiper Belt are called Dwarf planets. Pluto, Eris, Haumea & Makemake are the dwarf planets in the solar system. Ceres is somewhere between an asteroid and a dwarf planet so far no clear classification has been made.

Exoplanets – Planets that are situated outside the Sun's orbit, i.e, outside the solar system are known as exoplanets. The nearest exoplanet discovered so far is that of the star Proxima Centauri which is located 4.2 light-years from our planet.