Solar System

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The major planets...

The Solar System (sometimes stylized as "Sol System") consists of the sun, the planets orbiting it, together with moons, asteroids, comets, meteors and other objects gravitationally bound to the sun. There are four terrestrial, or rocky planets, and four gas giants. The terrestrial planets are nearer to the sun. It might be described as a "failed double star with some rocky debris present" in general terms.

In Cosmic Terms, it's sometimes addressed as a member Solar Interstellar Neighborhood, Milky Way Galaxy, Local Galactic Group, Virgo Supercluster, Local Superclusters, Observable Universe.


[edit] Planets

In order of distance from the sun the planets are:

  1. Mercury .39 AU
  2. Venus .72 AU
  3. Earth 1.0 AU
  4. Mars 1.5 AU
  5. Jupiter 5.2 AU
  6. Saturn 9.5 AU
  7. Uranus 19 AU
  8. Neptune 29 AU

1 AU (astronomical unit) = 149 598 000 kilometers

[edit] Dwarf planets

...and a few of the diddy ones too.

Pluto used to be considered a planet, but now is classified as a "dwarf planet" together with the former "minor planet" (asteroid) Ceres, the discord-producing Eris and some other objects in the Kuiper Belt. The rebranding of Pluto as a dwarf planet in 2006 was a minor pop science and media based storm, with many traditionalists demanding that Pluto be kept as a planet. However, the reasoning behind the classification was the rate of discovery of new objects in the outer solar system. Each new object could have been classed as a planet, but undoubtedly this could lead to a considerable definition problem (prior to 2006, "planet" wasn't even properly defined, there was no pressing need to until this point) with planets shrinking until they counted as asteroids. At least one object, Eris, is known to be larger than Pluto, and Ceres already had its planetary status revoked decades previously. "Plutoid" is a sub-category of distant dwarf planets to at least acknowledge Pluto as the first one discovered.

List of dwarf planets and dwarf planet candidates in order of increasing distance to the Sun, as of October 2011:

  • Ceres, the former largest and first discovered (in 1801) asteroid
  • Pluto, the former "ninth planet", discovered in 1930
  • Charon, Pluto's largest moon, big enough to pull the system's barycenter into the empty space between Pluto and Charon, discovered in 1978.
  • Orcus, dwarf planet candidate, discovered in 2004. May be even slightly closer to the Sun on average as Pluto.
  • Haumea, discovered in 2004, accepted as a dwarf planet in 2008
  • Quaoar, dwarf planet candidate, discovered in 2002
  • Makemake, discovered in 2005, accepted as a dwarf planet in 2008
  • 2007 OR10, dwarf planet candidate, discovered in 2007
  • Eris (a.k.a. 2003 UB313 or "Xena"), discovered in 2005, accepted as a dwarf planet in 2006. It was called "the tenth planet" in the media for some time, driving Planet X believers nuts nuttier.
  • Sedna, dwarf planet candidate, discovered in 2003. Really, really, really far away from the Sun.

[edit] Asteroids

The Solar System is also home to hundreds of thousands of asteroids, concentrated mostly in a belt between Mars and Jupiter, as well as innumerable icy bodies in the outer reaches of the system, which become comets when they are perturbed into the inner system and made visible by evaporation of part of their bodies by the heat of the sun.

[edit] Kuiper belt

The Kuiper belt is a "disk" extending to around 50 AU from the Sun that contains thousands of small, icy planetoids, including Pluto. The Kuiper belt is believed to be the source of short-period comets.[1]

[edit] Oort cloud

Relative postion of the Oort cloud and the Kuiper belt (the insert) to the rest of the Solar System.

Surrounding the solar system is an immense cloud of ice bodies called the Oort cloud. It lies roughly 50,000AU from the sun or about a quarter of the way to Proxima Centauri, the nearest star to our system.[2] Its vast distance means that it is only loosely bound to the solar system and that it is easily disturbed by other stars. Such disturbances are believed to be the source of all long-period comets.

A disc-shaped cloud of comets occupies some of the space between the Oort cloud and the Kuiper belt. This inner cloud is called the Hills Cloud.

[edit] External links

  • Solar System Scale Model, a site-model of the Solar System where both the sizes and the distances to the Sun are on the same scale. Prepare for lots of scrolling; the page is estimated to be a half-mile wide on a standard 72 dpi screen.
  • Bill Nye riding his bike along a scale model of the Solar System. "There's a lot of space in space!"

[edit] Footnotes

  1. Kuiper Belt, Solar System Exploration, NASA.
  2. Oort Cloud, Solar System Exploration, NASA.
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