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METEORITES
Meteor Terminology
ASTEROID
A large rocky body in space
larger than 10 meters
METEORITES...
COMET
A small body made of ice and dust
that leaves a tail of gas and ice
as it travels near the sun. Comet
trails cause meteor showers when
the Earth passes through them
Since the beginning of our
Solar System large and small fragments of rocks known as asteroids,
dating more than 4.5 billion years
old, orbit the sun in an area known
as the Asteroid Belt between Mars
METEOR
The light emitted from a
and Jupiter. Throughout the history
meteoroid as it enters the
of our solar system these remnants
atmosphere
from the formation of planets collide
METEOROID
and impact with one another. Some
A small rocky body
of these asteroids make their way
in space in size from
in orbits toward the inner planets,
microns to 10 meters
including Earth and our Moon. When
(~11 yards)
one of these objects crosses the path
METEOR SHOWERS
of Earth and enters our atmosphere
An event that occurs during the
it becomes a meteor. If fragments
same time each year in which a
make their way to the ground, they
number of meteors radiate from
are called meteorites.
the same point in the night sky
More than 1,000 tons of
extraterrestrial material falls to Earth
every day...most of which consists of
METEORITE
micro-metre-sized dust grains. Most
A fragment of a meteoroid or an
meteors, or “shooting stars”, burn
asteroid that survives passage
through the atmosphere and hits
up in our atmosphere before reachthe ground
ing the ground. Very few specimens
actually land on Earth and become
“named”. Even fewer meteorites that fall to Earth are recovered, fall. The largest majority of these meteorites have been found in
most fall into the ocean or on the land that is densely covered by the deserts of Northwest Africa (8,634) and on the continent of
vegetation making recovery nearly impossible.
Antarctica (41,113).
Meteorites are named after the site of the fall or find
Michigan is represented by ten official meteorites. Four
location, usually a town or landmark. Meteorites that are seen
were observed falls: Allegan (1899), Coleman (1994), Rose City
falling to Earth and recovered are call “falls”; those that are not
(1921) and Worden (1997). The Worden meteorite damaged a
seen to fall and discovered later are known as “finds”.
garage roof, ceiling and car. All four falls are stony meteorites.
There are three main classifications of meteorites which The remaining six Michigan meteorites are finds and classified
are determined by their nickel-iron content - Stony, Stony-Iron
as irons: Grand Rapids (1883), Iron River (1889), Kalkaska (1947),
and Iron. Sub-groups of meteorites exist within each of these
Reed City (1895), Seneca Township (1923) and Southern Michigan
classifications. One such example is Achondrites thought to
(1965).
originate from the 530 km (~329 mile) diameter asteroid Vesta.
Meteorites are the windows into the history of our solar
Martian and Lunar meteorites are also achondrites due to their
system. They have travelled millions of miles from the beginning
chemical composition. Each of these was ejected in large impact of time for us to study and advance the science of our universe.
events and eventually fell to Earth as meteorites.
For more information on this fascinating subject be sure
Today the Meteoritical Database kept by The Meteoritto check out your local library or the internet - what you learn
ical Society lists 52,928 approved meteorites worldwide. Of this
may take you on an unexpected trip through our vast solar system
number over 1,100 meteorites have been actually observed to
and beyond!
Stony
Meteorite Types
Stony meteorites or chondrites
are mixtures of olivine, pyroxenes
and nickel-iron minerals and
originate from the mantles and
crust of planets and asteroids.
Little spherical inclusions called
chondrules give the chondrite
meteorite its name. These spheres
of minerals are among the
oldest unchanged materials in
the solar system. Condrules are
not found in Earth rocks. Ordinary chondrites
are classified by the density and definition of
their condrules. Type 3 is well defined and
plentiful while types 4-5 are less distinct and
sparse. Ordinary chondrites are also classified
by their chemical and mineral composition.
H-Chondrites contain “high-iron” while L and
LL-Chondrites contain lower amounts of iron.
Stony meteorites represent 85% of meteorites
that fall to Earth.
Stony - Iron
Stony-Iron meteorites are
mixtures of nickel-iron
and silicate minerals and
originate from the thin
zone of melted rock that
lies between an asteroid’s
mantle and core. These
meteorites contain silicate
mineral olivine trapped in
the iron. Included in this
classification are Pallasites
and Mesosiderites. Pallasites contain
an equal amount of olivine and nickel
iron by volume and are among the
rarest and most beautiful meteorites.
Mesosiderites are composed of angular
rock fragments of different mineral
compositions. Stony-iron meteorites
represent less than 1% of meteorites
that fall to Earth.
Iron
Iron meteorites originate
from the heavy iron cores
of asteroids. Over long
periods of time, the cores
cooled slowly, allowing
iron crystals to grow.
These crystals show up
as cross-hatched patterns,
known as the Widmanstaetten pattern. Irons are
classified based on their
structural class, texture and chemical
classification. There are three basic
types: hexahedrites, octahedrites, and
ataxites. Each has a distinctive structure based on the amount of nickel it
contains. The structure depends on the
ratio of nickel to iron and the cooling
rate of the planetary core where it
originated.
Meteorite Strewnfield
This graphic, a detail from a
Chinese postage stamp issued in 2003,
commemorates the Jilin meteorite
fall. An outline of the Solar System at
the upper right shows the orbit of the
meteoroid and its impact with Earth.
To the left is an outline of China and a
drawing showing the explosion of the
meteor in Earth’s atmosphere and the
trail of debris depositing meteorites of
various sizes within an ellipse shaped
area known as a strewnfield.
Asteroid Belt
The asteroid belt is a disc of debris
left over from the formation of our Solar
System located in orbit between the planets
of Mars and Jupiter. Numerous irregularly
shaped bodies known as asteroids or minor
planets occupy this space. The largest object
in the asteroid belt is Ceres which is currently
being surveyed by the DAWN space mission.
Collisions between asteroids within
the belt can be violent with some fragments
eventually finding their way into the inner
Solar System leading to meteorite impacts
with the inner planets and Earth’s Moon.
Jupiter
Mars
(Graphic) Space Facts / Laurine Moreau
Abrams Planetarium, 755 Science Road, East Lansing, MI 48824
Main Phone: 517.355.4676; Information: 517.355.4672; www.abramsplanetarium.org
02/2016