Our Solar System

Our Solar System consists of the Sun, a family of planets, more than sixty moons orbiting the planets, millions of asteroids, and billions of comets. Our Solar System is an oasis of light, heat, and life. Read here to learn more about our Solar System and planets.

Classification

The nine bodies conventionally referred to as planets are often further classified in several ways:

by composition:

• terrestrial or rocky planets: Mercury, Venus, Earth, and Mars:

The terrestrial planet sare composed primarily of rock and metal and have relatively high densities, slow rotation, solid surfaces, no rings and few satellites.

• jovian or gas planets: Jupiter, Saturn, Uranus, and Neptune:

The gas planets are composed primarily of hydrogen and helium and generally have low densities, rapid rotation, deep atmospheres, rings and lots of satellites.

• Pluto.

by size:

• small planets: Mercury, Venus, Earth, Mars and Pluto.

The small planets have diameters less than 13000 km.

• giant planets: Jupiter, Saturn, Uranus and Neptune.

The giant planets have diameters greater than 48000 km.

[Mercury and Pluto are sometimes referred to as lesser planets (not to be confused with minor planets which is the official term for asteroids).

The giant planets are sometimes also referred to as gas giants.]

by position relative to the Sun:

• inner planets: Mercury, Venus, Earth and Mars.
• outer planets: Jupiter, Saturn, Uranus, Neptune and Pluto.

The asteroid belt between Mars and Jupiter forms the boundary between the inner solar system and the outer solar system.

by position relative to Earth:

• inferior planets: Mercury and Venus.

Closer to the Sun than Earth.

The inferior planets show phases like the Moon's when viewed from Earth.

• Earth.

• superior planets: Mars thru Pluto.

Farther from the Sun than Earth.

The superior planets always appear full or nearly so.

by history:

• classical planets: Mercury, Venus, Mars, Jupiter, and Saturn.

Known since prehistorical times.

Visible to the unaided eye.

• modern planets: Uranus, Neptune, Pluto.

Discovered in modern times.

Visible only with telescopes.

• Earth.