Solar system
A generic solar system (or planetary system) consists of at least one star and various orbiting objects (such as asteroids, comets, moonss, and planets). The term originated to describe the plantary system around Sol, the Latin name for our sun. The planet Earth is located within our solar system, which is usually just called the Solar system; others being referred to as planetary systems to avoid confusion. This terminology will be used below.
Solar system objects
There are a wide variety of objects present in the solar system that fall under various different categories. In recent years many of these categories have been found to be less clear-cut than once thought. This encyclopedia employs the following divisions:
- The Sun, a spectral class G2 star that contains 99.86% of system's mass.
- 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 moonss. For a complete listing, see that article.
- dust and other small particles that orbit these planets form planetary rings
- Space debris of artificial origin can be found in orbit around Earth.
- The planets were originally formed from planetesimals, sub-planetary bodies that accreted together during the first years of the solar system and no longer exist. The name is also sometimes used to refer to asteroids and comets in general, or to asteroids below 10km in diameter
- Asteroids
are
objects
smaller
than
planets
that
lie
roughly
within
the
orbit
of
Jupiter
and
are
composed
in
significant
part
by
non-volatile
minerals.
They
are
subdivided
into
the
near-Earth
asteroids,
which
are
further
subdivided
into
Atens,
Apolloss,
and
Amors.
- Asteroid moons are asteroids that orbit larger asteroids. They are not as clearly distinguished as planetary moons, sometimes being almost as large as their partner.
- 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 roughly boulder-sized or smaller, all the way down to dust. Dust within the solar system is responsible for the phenomenon of zodiacal light.
- Comets, which are composed largely of volatile ices and whose orbits are highly eccentric, generally having a periapsis within the orbit of the inner planets and an apoapsis out past 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 system.
- Centaurss, icy comet-like bodies that have less eccentric orbits that remain in the region between Jupiter and Neptune.
- Trans-Neptunian
objects,
icy
bodies
whose
mean
orbital
radius
lies
beyond
Neptune's.
These
are
further
subdivided:
- Kuiper belt objects, with orbits lying between 30 and 50 AU. 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, with orbits lying between 50,000 and 100,000 AU. This region is thought to be the origin of long-period comets.
-
Small
quantities
of
dust
are
present
throughout
the
solar
system,
and
is
responsible
for
the
zodiacal
light.
Some
of
the
dust
is
likely
interstellar
dust
from
outside
the
solar
system.
Origin and evolution of planetary systems
Planetary systems are generally believed to form as part of the same process which results in star formation; although, some argue that systems are formed by some kind of accidental "stellar near-collison". The more common theory argues that the objects of a planetary system developed from a solar nebula.
Orbit of the solar system
The solar system is part of the Milky Way galaxy, a spiral galaxy with a diameter of about 100,000