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, with distinct bands and four very large satellites.
- Saturn is the second largest planet, with a large and bright ring system.
- Uranus was discovered in 1781. It is tilted almost onto the plane of its orbit.
- Neptune was discovered in 1846 as a result of its perturbations of Uranus.
The outer planets all have ring systems, although all but Saturn's are faint.
Another aspect common to the gas giants is their many natural satellites, 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).
Read more about Outer Planets: Exploration, Mission Concepts
Famous quotes containing the words outer and/or planets:
“When human beings have been fascinated by the contemplation of their own hearts, the more intricate biological pattern of the female has become a model for the artist, the mystic, and the saint. When mankind turns instead to what can be done, altered, built, invented, in the outer world, all natural properties of men, animals, or metals become handicaps to be altered rather than clues to be followed.”
—Margaret Mead (1901–1978)
“Perhaps when distant people on other planets pick up some wave-length of ours all they hear is a continuous scream.”
—Iris Murdoch (b. 1919)