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Space Station Info >> Asteroid
Asteroid
An asteroid is a small, solid
object in our Solar System, orbiting the Sun.
An asteroid is an example of a minor planet (or
planetoid), which are much smaller than planets.
Most asteroids are believed to be remnants of
the protoplanetary disc which were not incorporated
into planets during the system's formation. Some
asteroids have moons. The vast majority of the
asteroids are within the main asteroid belt, with
elliptical orbits between those of Mars and Jupiter.
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The term "asteroid",
meaning star-like was coined in 1802 by
Sir William Herschel shortly after Olbers
discovered the second one, 2 Pallas, in
late March of the same year, to describe
their star-like appearance; the other then-known
planets all show discs, by comparison. He
also applied that term to the small moons
of the giant planets. The first scientific
paper to use the word in its title was published
in 1840 by Erman.
The exact definition of an asteroid
is unsettled. The term "Minor planet"
carries no strong suggestion about the composition
of the object or its general location in the solar
system, and some argue that not every minor planet
should be called an "asteroid".
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One way to classify asteroids
is in terms of size. A working definition is that
asteroids are larger than 50 m in diameter, distinguishing
them from meteoroids, which are typically boulder-sized
or smaller. The distinction is made because asteroids
are large enough to survive passage through Earth's
atmosphere and strike Earth largely intact while
the smaller meteoroids generally break up high
in Earth's atmosphere.
Thus, it would be safest to use the term "asteroid"
for Solar System objects that are bigger than
meteoroids, smaller than planets, and made out
of rock, not ice. See Solar System for a complete
taxonomy of objects in our system, and minor planet
for taxonomy of the sub planetary objects that
include asteroids. The term artificial asteroid
is sometimes used to designate man-made objects
which have ended up in solar orbits, such as the
Mariner IV probe.
Also see about
vAsteroids
In The Solar System
vAsteroid
Classification
vAsteroid
Discovery
vAsteroid
Exploration
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