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 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 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 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.
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."
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.
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.
removal of material from the surface of an object, including melting, evaporation, or erosion.
oral or written description of events.
type of stony meteorite containing no hardened droplets (chondrules).
nutrient containing carbon, hydrogen, oxygen, and nitrogen that is critical for all life.
generally or near an exact figure.
irregularly shaped planetary body, ranging from 6 meters (20 feet) to 933 kilometers (580 miles) in diameter, orbiting the sun between Mars and Jupiter.
person who studies space and the universe beyond Earth's atmosphere.
layers of gases surrounding a planet or other celestial body.
line separating geographical areas.
fragile or easily broken.
type of stony meteorite (chondrite) that contains the element carbon, usually in the form of organic compounds such as amino acids.
type of stony meteorite containing hardened droplets, called chondrules, of silicate minerals.
small droplet of silicate mineral found in stony meteorites.
type of sedimentary rock that is able to be shaped when wet.
arrangement of the parts of a work or structure in relation to each other and to the whole.
the extremely hot center of Earth, another planet, or a star.
rocky outermost layer of Earth or other planet.
type of mineral that is clear and, when viewed under a microscope, has a repeating pattern of atoms and molecules.
remains of something broken or destroyed; waste, or garbage.
type of crystal that is pure carbon and the hardest known natural substance.
very large, extinct reptile chiefly from the Mesozoic Era, 251 million to 65 million years ago.
to learn or understand something for the first time.
to fall apart and disappear.
microscopic particles of rocks or minerals drifting in space. Also called cosmic dust or space dust.
chemical that cannot be separated into simpler substances.
to attach firmly to a surrounding substance.
on the outside or outdoors.
process of complete disappearance of a species from Earth.
piece or part.
force produced by rubbing one thing against another.
state of matter with no fixed shape that will fill any container uniformly. Gas molecules are in constant, random motion.
collision or crash.
circular surface depression made by the impact of a meteorite.
to display or show.
rock, made of iron and nickel, that has crashed to Earth from outside the atmosphere.
molten rock, or magma, that erupts from volcanoes or fissures in the Earth's surface.
having to do with Earth's moon or the moons of other planets.
middle layer of the Earth, made of mostly solid rock.
fourth planet from the sun, between Earth and Jupiter.
very large or heavy.
category of elements that are usually solid and shiny at room temperature.
rocky debris from space that enters Earth's atmosphere. Also called a shooting star or falling star.
type of rock that has crashed into Earth from outside the atmosphere.
small, rocky body traveling around the sun.
dust-size particle of space debris that burns up as it enters Earth's atmosphere.
instrument used to view very small objects by making them appear larger.
inorganic material that has a characteristic chemical composition and specific crystal structure.
very small amount.
natural satellite of a planet.
Earth's only natural satellite.
chemical element with the symbol Ni.
type of silicate mineral.
to move in a circular pattern around a more massive object.
chemical substance that contains the element carbon.
type of stony-iron meteorite containing olivine or peridot crystals embedded in an iron-nickel webbing.
small piece of material.
large, spherical celestial body that regularly rotates around a star.
to fall sharply.
simple or crude.
memento or surviving object of the past.
natural substance composed of solid mineral matter.
vehicle that remotely explores a region, such as the surface of a moon, planet, or other celestial body.
solid material transported and deposited by water, ice, and wind.
most common group of minerals, all of which include the elements silicon (Si) and oxygen (O).
the sun and the planets, asteroids, comets, and other bodies that orbit around it.
vehicle designed for travel outside Earth's atmosphere.
individual organism that is a typical example of its classification.
rock, made of nearly equal parts metal and silicate minerals, that has crashed to Earth from outside the atmosphere.
rock, made of silicate minerals, that has crashed to Earth from outside the atmosphere.
to put underwater.
star at the center of our solar system.
sudden, violent explosion of a massive star.
physical or tactile characteristics of a substance.
having to do with heat or temperature.
very large or important.
to cause or begin a chain of events.