Solar system objects
The wide variety of objects that exist in the solar system fall into
several categories. In recent years many of these categories have been
found to be less clear-cut than once thought.
- The Sun is a spectral class G2 star that contains 99.86% of the system's
- The planets of the solar system are those nine bodies traditionally
labelled as such: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus,
Neptune and Pluto.
- Sizeable objects that orbit these planets are moons. For a complete
listing, see that article.
- Dust and other small particles that orbit these planets form planetary
- Space debris of artificial origin that can be found in orbit around
- Planetesimals, from which the planets were originally formed, are
sub-planetary bodies that accreted during the first years of the solar
system and that no longer exist. The name is also sometimes used to
refer to asteroids and comets in general, or to asteroids below 10km
- Asteroids are objects smaller than planets that lie roughly within
the orbit of Jupiter and are composed in significant part of nonvolatile
minerals. They are subdivided into asteroid groups and asteroid families
based on their specific orbital characteristics.
- Asteroid moons are asteroids that orbit larger asteroids. They
are not as clearly distinguished as planetary moons, sometimes being
almost as large as their partners.
- Trojan asteroids are located in either of Jupiter's L4 or L5 points,
though the term is also sometimes used for asteroids in any other
planetary Lagrange point as well.
Meteoroids are asteroids that range in size from roughly boulder
sized to particles as small as dust.
- Comets are composed largely of volatile ices and have highly eccentric
orbits, generally having a periapsis within the orbit of the inner planets
and an apoapsis beyond Pluto. Short-period comets exist with apoapses
closer than this, however, and old comets that have had most of their
volatiles driven out by solar warming are often categorized as asteroids.
Some comets with hyperbolic orbits may also originate outside the solar
- Centaurs are icy comet-like bodies that have less-eccentric orbits
so that they remain in the region between Jupiter and Neptune.
- Trans-Neptunian objects, which are icy bodies whose mean orbital radius
lies beyond Neptune's. These are further subdivided:
- Kuiper belt objects have orbits lying between 30 and 50 AU. This
is thought to be the origin for short-period comets. Pluto is sometimes
classified as a Kuiper belt object in addition to being a planet,
and a class of Kuiper belt objects with Pluto-like orbits are called
Plutinos. The remaining Kuiper belt objects are classified as Cubewanos
in the main belt and scattered disk objects in the outer fringes.
- Oort cloud objects, currently hypothetical, have orbits lying
between 50,000 and 100,000 AU. This region is thought to be the
origin of long-period comets.
- The newly discovered object Sedna, with a highly elliptical orbit
extending from about 76 to 850 AU, does not obviously fit in either
category, although its discoverers argue that it should be considered
a part of the Oort cloud.
- Small quantities of dust are present throughout the solar system and
are responsible for the phenomenon of zodiacal light. Some of the dust
is likely interstellar dust from outside the solar system.
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