Craters on the Moon
and other planets were once, thought to be created by old volcanoes.
This concept was thought to be the same for Earth too, but around the
year 1900, it was proven otherwise at a place now called Meteor Crater
in Arizona. Rocks, including large ones, do collide or fall to the Earth,
the Moon and other planets such as Mars. Many believe that the dinosaurs
were killed off by a large (6 miles in size) meteor collision with Earth.
Large impact craters create new rocks called tektites, which are like
volcanic glass, and impact melts called breccias, and fractured rocks
called shattercones.
"Shooting Stars"
were once thought to be stars falling from their place in the heavens,
never to be seen again. But we now know that these shooting stars are
actually meteors that pass through our atmosphere. The typical shooting
star is a small spec of rock that burns up in our atmosphere from friction.
If a bigger meteor fell you would definitely notice a difference in
the brightness and size of the streak. A large meteor seen locally would
brighten the sky in the daytime, and often creates a "sonic boom".
Meteorites are meteors
that land on Earth. They are called a Fall if witnessed by people when
they fall, or Finds when people find them and no one saw them come down
in an area. A new or recent fall will typically have a dark, often black
"fusion crust" on one or more sides which demonstrates the
heat generated during its’ flight through our atmosphere. The
rocks get cooked, and melt away. Crust colors can vary with different
types of meteorites.
Most meteorites have
a nickel-iron metal in them that is attracted to magnets. This attraction
to magnets is called paramagnetism. Most achondrites have very little
metal are not attracted to magnets or metal detectors.
Where do meteorites
come from? The main source of meteorites is from the Asteroid Belt,
which lies between Mars and Jupiter. This belt is full of orbiting asteroids
that range in size from small particles to rocks up to 10 miles in length.
These pieces are thought by some to be the parts of a planet that never
came together. When asteroids collide with each other, they create new
pieces that may fall out of orbit towards Earth, or to other planets
or moons that eventually may grab them by gravity forces. They often
hit a planet’s atmosphere moving at 10,000 to 20,000 MPH (WOW).
Other sources of meteorites include the Moon, Mars, and comets.
Most meteorites are
thought to be about 4.56 billion years old, which is slightly older
than Earth. Planetoid meteorites including the Mars and the Moon are
usually younger.
There are three main
types of meteorites. Stone(93%), Iron(6%) and Stony-iron(1%). 86% of
the total represent stones are estimated to be from the undifferentiated
(unchanged or changed little) or chondrite (stone) category. About 7%
of the total are differentiated (changed a lot) stones that are called
Achondrites. A very small % are unique, one of a kind types that don’t
easily fit into a distinct category. These estimates are based on the
recorded falls, and the types that have fallen with them, and by number
of finds.
Stone meteorites are
split into two major categories: Chondrites (starts with a ‘k’
sound) and Achondrites, meaning rocks with or without chondrules, which
are small rounded ball-like structures made only out in space. You will
not find rocks made on planets , like Earth, that have chondrules in
them. The details on how chondrules are made are still a mystery. Many
ideas have been proposed, but we still don’t know for sure.
Most meteorites
that are from the Asteroid Belt are Chondrule filled stony rocks with
a little to a lot of metal inside. Others are the Iron (iron-nickel)
rocks that are all metal, or a unique mixture of both kinds, the Stony-Irons.
Achondrites do occur in the Belt, and are usually associated with larger
planet-like differentiated pieces. Mars and Moon meteorites are also
Achondrites, and they are obviously closer to us than the Asteroid Belt
asteroids are.
Summary of
Meteorite Types
Chondrites (Stone)
There are about 15 different named types of Chondrites including:
- H or high metal
- L or low metal
- LL or very low metal
- Various C-meteorites for Carbonaceous (comets are
thought to be in this class)
Achondrites
(Stone)
There are about 10 different types of Achondrites including:
- Shergottites, Nakhlites, and Chassignite
- Lunar (from the Moon)
- Eucrites
- Diogenites
- Howardites (mixture of Eucrites and Diogenites)
- Aubrites
- Angrites
- Urelites
Stony-Iron
There are two types of Stony-Iron meteorites:
Iron
There are three main types of Iron meteorites with many sub-categories
- Hexahedrite
- Octahedrite
- Ataxite
Facts and
Fiction of Falls and Finds
Meteorite
Falls:
Meteorite Falls can
happen all over the earth. Most fall into the oceans that cover the
majority of earth.
What we usually see as a falling star is just a small bit of rock that
burns up in the atmosphere.
Fireball’s which can "light up the sky", day or night,
are the meteors that will produce meteorites. They often start out a
chunk as big as a car or so, only to break up and burn away to usually
less than a hundred pounds for the total weight of meteorites found
for a particular fall.
Witnessed falls are usually given the name of the nearest town or landmark.
The same can be said for most finds.
Fresh fusion crust is probably the most obvious feature of a new fall.
It does not take long for the effects of earth to start breaking down
a meteorite.
Meteorite
Finds:
Finds can also happen
all over the earth. The majority however are found in the desert regions
of the world, particularly north Africa and the middle east. Antarctica
is also a rich location for meteorites finds. The reduced weathering
effect in these regions is one of the reasons more are found. Wet or
jungle like climates/terrain make finding falls and new finds difficult.
Iron meteorites are found more often (higher %) than they actually fall
because they are more durable over time, and they look like what people
think are meteorites.
Meteorite
Tidbits:
- They are not hot when they first land on earth.
Maybe warm.
- They are not radioactive, nor do they have healing
powers.
- They are hard to find and difficult to acquire
or purchase????
- To date, not one person has been reported killed
by a meteorite.