The asteroid belt, a band of boulders 
and cosmic debris that orbits the sun 
between the orbits of Mars and 
Jupiter, is believed to be the source 
of most meteorites large enough to 
be seen on Earth with the naked eye. 
■tf-. K . 
Meteorites are pieces of rock that 
rain from the heavens. It may be dif- 
ficult to believe that rocks can fall 
from the sky — especially when looking 
at such large objects as the Ahnighito, 
the 34-ton hunk of Cape York me- 
teorite that is the centerpiece of the 
new Arthur Ross Hall of Meteorites 
at the American Museum of Natural 
History. Nevertheless, rocks do drop 
out of the sky. More than 3,000 of 
them have been collected and placed 
in museums and university laborato- 
ries around the world, where they can 
be gazed at, studied, and analyzed. 
For museum visitors, meteorites 
may be the oldest objects yet seen 
close up. For scientists, meteorites 
serve as messengers from the outer 
realms of space, bearing information 
about the early solar system. 
Many meteorites are now believed 
to come from the asteroid belt, a band 
of debris and rocks that orbits the 
sun about 200 to 300 million miles 
out, between the orbits of Mars and 
Jupiter. It is the shape of the me- 
teorites’ orbits that suggests that these 
objects come from the asteroid belt. 
This view is supported by the fact 
that the asteroid belt marks the outer 
limit of the terrestrial, or rocky, plan- 
ets: Mercury, Venus, Earth and its 
moon, and Mars. Beyond the asteroid 
belt, the only rocky bodies known are 
the small satellites, or moons, of the 
gigantic gas planets such as Jupiter 
and Saturn. It is important to note, 
however, that not all meteorites come 
from asteroids. There are also tiny 
meteorites, about the size of dust par- 
ticles, that are believed to come from 
comets. 
Whatever their origin, meteorites 
have been classified according to their 
most obvious physical characteristics 
into three main types: stony meteor- 
ites, composed predominantly of sili- 
cate minerals; iron meteorites, made 
up, as their name suggests, almost en- 
tirely of metallic iron; and stony-irons, 
which are half stony and half metallic. 
Within these main types there are 
many subdivisions and differences. 
53 
