Meteorites are space rocks that fall to Earth’s surface. 
 
Meteorites are the last stage in the existence of these type of space rocks. Before they were meteorites, the rocks were meteors. Before they were meteors, they were meteoroids. Meteoroids are lumps of rock or metal that orbit the sun. Meteoroids become meteors when they crash into Earth’s atmosphere and the gases surrounding them briefly light up as “shooting stars.” While most meteors burn up and disintegrate in the atmosphere, many of these space rocks reach Earth’s surface in the form of meteorites.
 
Dust-sized particles called micrometeorites make up 99 percent of the approximately 50 tons of space debris that falls on the Earth’s surface every day. Some meteorites, however, are as large as boulders. 
 
The largest meteorite found on Earth is the Hoba meteorite discovered in Namibia in 1920. The Hoba meteorite weighs roughly 54,000 kilograms (119,000 pounds). The Hoba meteorite is so big, and so heavy, it has never been moved from where it was found!
 
Most meteorites look very much like rocks found on Earth, except meteorites usually have a dark, burned exterior. This exterior is formed as friction from the atmosphere melts the meteorite as it crashes toward Earth. Known as thermal ablation, this process can also give meteorites a roughened, smooth, or thumbprint surface. Thermal ablation creates these different textures due to different chemicals present in the meteorite.
 
Meteorites crash through the atmospheres of all planets and moons in our solar system. Some planets and moons don't have enough atmosphere to break apart meteors, resulting in large meteorites. These larger meteorites create deep, round impact craters that can be found all over our Moon, Mercury, and Mars. In 2005, the first meteorite found on another planet was discovered by Opportunity, one of NASA’s Mars rover spacecraft. In 2014, Opportunity’s sister spacecraft, Curiosity, discovered a meteorite that was 2 meters (7 feet) wide, making it the largest yet discovered on Mars.
 
Types of Meteorites
 
More than 60,000 meteorites have been found on Earth. Scientists have divided these meteorites into three main types: stony, iron, and stony-iron. Each of these types has many sub-groups.
 
Stony Meteorites
Stony meteorites are made up of minerals that contain silicates—material made of silicon and oxygen. They also contain some metal—nickel and iron. There are two major types of stony meteorites: chondrites and achondrites.
 
Chondrites themselves are classified into two major groups: ordinary and carbonaceous. Ordinary chondrites are the most common type of stony meteorite, accounting for 86 percent of all meteorites that have fallen to Earth. They are named for the hardened droplets of lava, called chondrules, embedded in them. Chondrites formed from the dust and small particles that came together to form asteroids in the early solar system, more than 4.5 billion years ago. Because they were formed at the same time as the solar system, chondrites are integral to the study of the solar system’s origin, age, and composition. 
 
Ordinary chondrites can be classified into three main groups. The groups indicate the meteorite’s quantity of iron. The H chondrite group has a high amount of iron. The L chondrite group has a low amount of iron. The LL group has a low amount of iron and a low amount of metal in general.
 
Carbonaceous chondrites are much more rare than ordinary chondrites. Astronomers think carbonaceous chondrites formed far away from the sun as the early solar system developed. As their name implies, carbonaceous chondrites contain the element carbon, usually in the form of organic compounds such as amino acids. Carbonaceous chondrites also often contain water or material that was shaped by the presence of water.
 
Like ordinary chondrites, carbonaceous chondrites can be more minutely classified based on their mineral composition. All groups of carbonaceous chondrites are marked with a two- or three-letter code starting with C. Carbonaceous chondrites are often named after the first specimen of that type recovered. The CI group, for instance, is named after the Ivuna meteorite, which crashed into Tanzania in 1938. CI meteorites have a high amount of carbon, as well as clays. Carbonaceous chondrites can also be named after the place where the first specimen of the type was found. The CV group is named after a meteorite that crashed near the city of Vigarano, Italy, in 1910. The most famous CV meteorite is probably the Allende meteorite, which fell to Earth near Pueblo de Allende, Chihuahua, Mexico, in 1969. The Allende meteorite has thousands of tiny chondrules made of the mineral olivine. The Allende meteorite also has grains of a special kind of carbon—diamonds. These diamonds are actually older than the solar system, and astronomers think they were produced as blast material from a nearby, ancient supernova.
 
Achondrites do not contain the lava droplets (chondrules) present in chondrites. They are very rare, making up about 3 percent of all known meteorites. Most achondrites form from the brittle outer layers of asteroids, which are similar to Earth’s crust.
 
There are many classifications of achondrites. The “primitive achondrite” group, for instance, has a very similar mineral composition to chondrites. Lunar meteorites are achondrites that crashed to Earth from the Moon, while Martian achondrites crashed to Earth from our neighbor planet, Mars.
 
Very few meteorites, only about 0.2 percent, come from Mars and the Moon. These achondrites are the results of Mars and the Moon’s own meteorite impacts. Large meteorites hit the surface of Mars and the Moon, blasting off bits of rock. These rock bits rarely make their way to our atmosphere as meteors and even more rarely hit the Earth’s surface. 
 
Iron Meteorites
Iron meteorites are mostly made of iron and nickel. They come from the cores of asteroids and account for about 5 percent of meteorites on Earth.
 
Iron meteorites are the most massive meteorites ever discovered. Their heavy mineral composition (iron and nickel) often allows them to survive the harsh plummet through Earth’s atmosphere without breaking into smaller pieces. The largest meteorite ever found, Namibia’s Hoba meteorite, is an iron meteorite.
 
Stony-Iron Meteorites
Stony-iron meteorites have nearly equal amounts of silicate minerals (chemicals that contain the elements silicon and oxygen) and metals (iron and nickel). 
 
One group of stony-iron meteorites, the pallasites, contains yellow-green olivine crystals encased in shiny metal. Astronomers think many pallasites are relics of an asteroid’s core-mantle boundary. Their chemical composition is similar to many iron meteorites, leading astronomers to think maybe they came from different parts of the same asteroid that broke up when it crashed into Earth’s atmosphere.
 
Meteorite Impact Craters
 
Meteorites crash through the Earth’s atmosphere with tremendous force. The largest meteorites leave enormous holes in the ground called impact craters. 
 
The best-preserved impact crater in the world is the Barringer Meteorite Crater, near Winslow, Arizona. There, more than 50,000 years ago, a meteorite weighing about 270,000 metric tons (300,000 tons) slammed into the Earth with the force of 2.5 million tons of TNT. The impact blasted a hole 1 kilometer (.6 miles) wide and about 230 meters (750 feet) deep. The fragments left of the space rock show that it was an iron meteorite.
 
More than a hundred impact craters have been identified on Earth. Perhaps the most famous is the Chicxulub Crater, in Yucatan, Mexico. The Chicxulub Crater can be identified on land, beneath dozens of meters of sediment, although about half of the feature is submerged in the Gulf of Mexico. It is one of the larges impact craters ever discovered on Earth.
 
Despite its size, the Chicxulub Craber is famous for another reason. Many scientists think the large meteorite that created the Chicxulub Crater—measuring roughly 10 kilometers (6 miles) wide—triggered the extinction of the dinosaurs and other animal and plant life 65 million years ago. 
meteorite
Deserts, such as Saudi Arabia (above) and Antarctica, are excellent places to search for meteorites.
Natural Hazards
Most meteorites fall to Earth harmlessly. Sometimes, however, they can cause great damage. The extinction of most life on Earth 65 million years ago is a good example of that. A less catastrophic impact hit a driveway in Peekskill, New York, in 1992. Although no one was harmed, the meteorite slammed through the trunk of a parked Chevrolet Malibu, barely missing the gas tank, before creating a small impact crater beneath the car. The Chevy is nicknamed the "Peekskill Meteorite Car."
Ablation Blackening
Thermal ablation, the process that burns off the surface layer of a meteorite and causes it to appear blackened, is the same process that blackens the outside of returning spacecraft, such as tiles on the space shuttle.
Mars and the Moon
As of July 2014, there were 133 Martian meteorites and 183 lunar meteorites  found on Earth—not a lot. Scientists are able to tell the rocks came from Mars and the Moon because their composition matches chemical analysis of rocks conducted during NASA’s robotic explorations of Mars and the “moon rocks” recovered during the Apollo lunar missions. 

Meteorite or Meteorwrong?
How can you tell if that rock you found fell from the sky? First of all, meteorites get burned when they enter Earths atmosphere, so they are usually black and crusty on the outside. Also, meteoriteseven stony meteoritescontain iron, so a magnet will stick to them.

Rocky Cookie
The best place to hunt for meteorites is in Antarctica. Because most of Antarctica is covered in ice and snow, rocky meteorites stand out like chocolate chips in a cookie.

ablation
Noun

removal of material from the surface of an object, including melting, evaporation, or erosion.
account
Noun

oral or written description of events.
achondrite
Noun

type of stony meteorite containing no hardened droplets (chondrules).
amino acid
Noun

nutrient containing carbon, hydrogen, oxygen, and nitrogen that is critical for all life.
ancient
Adjective

very old.
approximately
Adjective

generally or near an exact figure.
asteroid
Noun

irregularly shaped planetary body, ranging from 6 meters (20 feet) to 933 kilometers (580 miles) in diameter, orbiting the sun between Mars and Jupiter.
astronomer
Noun

person who studies space and the universe beyond Earth's atmosphere.
atmosphere
Noun

layers of gases surrounding a planet or other celestial body.
boulder
Noun

large rock.
boundary
Noun

line separating geographical areas.
brittle
Adjective

fragile or easily broken.
carbonaceous chondrite
Noun
type of stony meteorite (chondrite) that contains the element carbon, usually in the form of organic compounds such as amino acids.
chondrite
Noun

type of stony meteorite containing hardened droplets, called chondrules, of silicate minerals.
chondrule
Noun

small droplet of silicate mineral found in stony meteorites.
clay
Noun

type of sedimentary rock that is able to be shaped when wet.
composition
Noun

arrangement of the parts of a work or structure in relation to each other and to the whole.
core
Noun

the extremely hot center of Earth, another planet, or a star.
crust
Noun

rocky outermost layer of Earth or other planet.
crystal
Noun

type of mineral that is clear and, when viewed under a microscope, has a repeating pattern of atoms and molecules.
debris
Noun

remains of something broken or destroyed; waste, or garbage.
diamond
Noun

type of crystal that is pure carbon and the hardest known natural substance.
dinosaur
Noun

very large, extinct reptile chiefly from the Mesozoic Era, 251 million to 65 million years ago.
discover
Verb

to learn or understand something for the first time.
disintegrate
Verb

to fall apart and disappear.
dust
Noun

microscopic particles of rocks or minerals drifting in space. Also called cosmic dust or space dust.
element
Noun

chemical that cannot be separated into simpler substances.
embed
Verb

to attach firmly to a surrounding substance.
enormous
Adjective

very large.
exterior
adjective, noun

on the outside or outdoors.
extinction
Noun

process of complete disappearance of a species from Earth.
fragment
Noun

piece or part.
friction
Noun

force produced by rubbing one thing against another.
gas
Noun

state of matter with no fixed shape that will fill any container uniformly. Gas molecules are in constant, random motion.
harsh
Adjective

extreme.
impact
Noun

collision or crash.
impact crater
Noun

circular surface depression made by the impact of a meteorite.
indicate
Verb

to display or show.
integral
Adjective

very important.
iron meteorite
Noun

rock, made of iron and nickel, that has crashed to Earth from outside the atmosphere.
lava
Noun

molten rock, or magma, that erupts from volcanoes or fissures in the Earth's surface.
lunar
Adjective

having to do with Earth's moon or the moons of other planets.
mantle
Noun

middle layer of the Earth, made of mostly solid rock.
Mars
Noun

fourth planet from the sun, between Earth and Jupiter.
massive
Adjective

very large or heavy.
metal
Noun

category of elements that are usually solid and shiny at room temperature.
meteor
Noun

rocky debris from space that enters Earth's atmosphere. Also called a shooting star or falling star.
meteorite
Noun

type of rock that has crashed into Earth from outside the atmosphere.
meteoroid
Noun

small, rocky body traveling around the sun.
micrometeorite
Noun

dust-size particle of space debris that burns up as it enters Earth's atmosphere.
microscope
Noun

instrument used to view very small objects by making them appear larger.
mineral
Noun

inorganic material that has a characteristic chemical composition and specific crystal structure.
minute
Adjective

very small amount.
moon
Noun

natural satellite of a planet.
Moon
Noun

Earth's only natural satellite.
nickel
Noun

chemical element with the symbol Ni.
olivine
Noun

type of silicate mineral.
orbit
Verb

to move in a circular pattern around a more massive object.
organic compound
Noun

chemical substance that contains the element carbon.
pallasite
Noun

type of stony-iron meteorite containing olivine or peridot crystals embedded in an iron-nickel webbing.
particle
Noun

small piece of material.
planet
Noun

large, spherical celestial body that regularly rotates around a star.
plummet
Verb

to fall sharply.
primitive
Adjective

simple or crude.
quantity
Noun

amount.
relic
Noun

memento or surviving object of the past.
rock
Noun

natural substance composed of solid mineral matter.
rover
Noun

vehicle that remotely explores a region, such as the surface of a moon, planet, or other celestial body.
sediment
Noun

solid material transported and deposited by water, ice, and wind.
silicate
Noun

most common group of minerals, all of which include the elements silicon (Si) and oxygen (O).
solar system
Noun

the sun and the planets, asteroids, comets, and other bodies that orbit around it.
spacecraft
Noun

vehicle designed for travel outside Earth's atmosphere.
specimen
Noun

individual organism that is a typical example of its classification.
stony-iron meteorite
Noun

rock, made of nearly equal parts metal and silicate minerals, that has crashed to Earth from outside the atmosphere.
stony meteorite
Noun

rock, made of silicate minerals, that has crashed to Earth from outside the atmosphere.
submerge
Verb

to put underwater.
sun
Noun

star at the center of our solar system.
supernova
Noun

sudden, violent explosion of a massive star.
texture
adjective, noun

physical or tactile characteristics of a substance.
thermal
Adjective

having to do with heat or temperature.
tremendous
Adjective

very large or important.
trigger
Verb

to cause or begin a chain of events.

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    Aug. 1, 2014

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