Where Do Meteorites Come
Meteorites are ambassadors from afar,
providing scientists with unique opportunities to investigate
the physical and chemical nature of distant worlds. Most
meteorites originate in asteroids, although a few meteorites come from
larger planetary bodies like the Moon or Mars.
Asteroids- Most of the meteorites in our
collections are fragments of asteroids, minor planets that circle the Sun
between the orbits of Mars and Jupiter. There are millions of asteroids, and
more are discovered every years. They come in all sizes, with diameters ranging from a few feet to hundreds of miles.
asteroid reflects sunlight, some wavelengths of
light (certain colors) are absorbed by the asteroid's surface materials whereas
the remaining wavelengths are reflected back to
space. Astronomers can study the "reflectance spectra"
of asteroids to learn about their compositional
and structural makeup, and such studies show
that asteroids are made of variable amounts of
stone and iron (just like meteorites). In a few cases, scientists have been able to pair individual
meteorites with specific parent asteroids.
The left photo shows the asteroid belt (white dots). The
right photo shows a closeup of the Gaspra asteroid (NASA image).
Asteroids do not have stable orbits like those of the major planets. Gravitational forces between asteroids and neighboring
Mars and Jupiter, as well as collisions between asteroids, occasionally
deflect asteroids from their normal orbits. Most of
these rogue bodies are lost to the emptiness of space, but inevitably some
fragments will intersect the
Earth’s orbit and may fall to Earth's surface as meteorites.
Planetary Meteorites- While most meteorites hail
from the asteroid belt, we are confident that a minority of the specimens in our
collections comes from the Moon and Mars. These "planetary meteorites"
were launched from their parent planets by high velocity impacts that set the
stage for a
transfer of rocks between planets. The cratered surface of our Moon illustrates the importance of impact processing during its history.
The Earth's surface would be similarly pot-marked, but traces of impacts are rapidly overprinted by
Earth's dynamic forces (erosion, tectonics,
and volcanism) that constantly reshape our landscape.
The Moon (left) and Mars (right) are the parent planets for a minority of
meteorites (NASA images).