What is "outer planets"

n. (outer planet English)

The outer planets are those planets in the Solar System beyond the asteroid belt, and hence refers to the gas giants, which are in order of their distance from the Sun:

• Jupiter is the largest planet in the Solar System. It has four very large satellites (moons).
• Saturn is the second-largest planet, with a large and bright ring system.
• Uranus is the third-largest planet and the least massive of the four outer planets. It is tilted almost onto the plane of its orbit.
• Neptune is the fourth-largest planet, as smallest of the four outer planets, but third-most massive. It has one big retrograde moon and many small ones.

The outer planets all have ring systems, although all but Saturn's are faint when viewed from Earth.

Another aspect common to the gas giants is their many natural satellites (moons), two of which are larger than the planet Mercury (Jupiter's Ganymede and Saturn's Titan). That pair and Io, Callisto, Europa, and Triton, are larger than Pluto and Eris.

This region of space is also occupied by centaurs, various fields of trojans, and many comets.

Pluto was considered to be an outer planet from its discovery in 1930 until its reclassification as a dwarf planet in 2006 (see also: Kuiper belt).