Station Info :: Asteroids
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.
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".
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
Asteroids In The Solar System