Astromaterials Research & Exploration Science
METEORITE FALLS

WHAT ARE METEORITES?

WHAT ARE METEORITES?

WHAT ARE METEORITES?

A meteorite is a solid piece of debris from an object, such as a comet, asteroid, or meteoroid, that originates in outer space and survives its passage through the atmosphere to reach the surface of a planet or moon.
A meteorite is a solid piece of debris from an object, such as a comet, asteroid, or meteoroid, that originates in outer space and survives its passage through the atmosphere to reach the surface of a planet or moon.
When the object enters the atmosphere, various factors like friction, pressure, and chemical interactions with the atmospheric gases cause it to heat up and radiate that energy. It then becomes a meteor and forms a fireball, also known as a shooting star or falling star; astronomers call the brightest examples "bolides." Meteorites vary greatly in size. For geologists, a bolide is a meteorite large enough to create a crater.
Meteorites have traditionally been divided into three broad categories: stony meteorites are rocks, mainly composed of silicate minerals; iron meteorites that are largely composed of metallic iron-nickel; and, stony-iron meteorites that contain large amounts of both metallic and rocky material. Modern classification schemes divide meteorites into groups according to their structure, chemical and isotopic composition and mineralogy.

TYPES OF METEORITES

STONY METEORITES

Stony meteorites are by far the most common. More than 95% of meteorites observed to fall to Earth are stony. They can be divided into chondrites and achondrites. Both types are composed mostly of silicate minerals, but the great majority also contain metallic iron in small-scattered grains.
Chondrites are named for their most prominent feature - millimeter-sized spherical bodies called chondrules. These chondrules (from the Greek for small sphere) formed 4.5 billion years ago in the Solar Nebula - the cloud of gas and dust from which the Sun, planets, asteroids, and comets formed. Chondrules are not found in terrestrial rocks. These chondrules, along with small mineral grains, accreted to form asteroids during the birth of the Solar System. Chondrites are, by far, the most abundant type of stony meteorite.
Less common, comprising only a few percent of all meteorites, are achondrites. These are also stony meteorites composed primarily of silicates, but these meteorites have experienced familiar geologic processes of melting and differentiation - although these happened long ago. Most achondrites formed on asteroids during the birth of the Solar System, but a small number formed on Mars and the Moon.

STONY-IRON METEORITES

Stony-iron meteorites, contain about equal proportions of metal and silicate material, and are rare (less than 2% of all known meteorites). Stony-iron meteorites form in places where metal and silicate are mixed.
One type of stony-iron are pallasites - rocks composed of a network of iron-nickel metal surrounding a greenish, silicate mineral called olivine. Pallasites probably form when the olivine-rich mantle of an asteroid mixes with the metallic core. Mesosiderites are mixtures of iron-nickel metal and basalt and probably formed by the collision of two asteroids.

IRON METEORITES

Iron meteorites are really composed of iron and nickel and are extremely dense. They are pieces of the cores of asteroids. Early in Solar System history, asteroids melted and the dense iron-nickel metal sank to the center to form a core - much like the Earth has a core. Iron meteorites are the samples of the cores of ancient worlds.
While they are rare among meteorites seen to fall to Earth (only a few percent), they are among the most common type of meteorites in our collections, because they can be recognized long after their fall, are very different from Earth rocks, and are resistant to weathering.
One of the most distinguishing features of meteorites is the presence of the Widmanstatten pattern - the distinctive series of bands in geometric patterns. This pattern is created by the intergrowth of two different iron-nickel minerals formed during very slow cooling (a few degrees every million years) in the core of the asteroid. The presence of nickel is a universal feature of iron meteorites.

AGE & ORIGINATION

Meteorites range in age. The oldest particles in a meteorite, calcium-aluminum-rich inclusions from carbonaceous chondrites, have been dated at 4.56 billion years old. Meteorites that originate from asteroids are all ~4.5 billion years old. Meteorites that originate from the Moon range in age from 4.5 to 2.9 billion years old. Meteorites that originate on Mars range in age from 4.5 billion years old to 200 million years old.
Most meteorites are believed to originate in the asteroid belt between Mars and Jupiter, and were formed early in the history of the Solar System ~4.56 billion years ago. These fragments of asteroids were either knocked out of their orbit of the Sun, and into Earth-crossing orbits, through collisions with other objects, or through the interaction of gravitational forces exerted by the Sun and Jupiter.

REFERENCES

  1. Wikipedia: Meteorite wikipedia.org. Retrieved on 20 June 2018.
  2. Smithsonian Institution mineralsciences.si.edu. Retrieved on 20 June 2018.
  3. Arizona State University meteorites.asu.edu. Retrieved on 20 June 2018.

METEORITES 101

This step-by-step guide will show you how to locate meteorite fall sites using radar software and weather data along with info provided by reporting agencies and monitoring systems.
These instructions will show you how to best preserve the meteorites you discover and how to make contact with the organizations that are willing to accept and analyze your find.
It turns out that meteorites have provided us a lot of scientific insight, not only into the origins of our solar system and planet Earth, but what the future might hold for mankind.
There's a lot going on in the study of meteorites, both here at NASA and in other places. Here are a few links to the people and institutions who are leading the research in this field.

METEORITES 101

This step-by-step guide will show you how to locate possible meteorite fall sites using radar software and weather data along with info provided by reporting agencies and monitoring systems.
These instructions will show you how to best preserve the meteorites you discover and how to make contact with the organizations that are willing to accept and analyze your find.
It turns out that meteorites have provided us a lot of scientific insight, not only into the origins of our solar system and planet Earth, but what the future might hold for mankind.
There's a lot going on in the study of meteorites, both here at NASA and in other places. Here are a few links to the people and institutions who are leading the research in this field.

RECENT EVENTS

Learn more about Probable Fall near Carrollton, AL

Probable Fall near Carrollton, AL

November 10, 2018

This event was an early morning fireball over the Mississippi-Alabama border, that was reported by 17 eyewitnesses. This is recorded as American Meteor Society event number 4,773 for 2018.

Learn more about Battle Mountain, Nevada

Battle Mountain, Nevada

August 22, 2012

This event was a large meteorite fall that was lightly reported and would not have been located without weather radar data. This is recorded as American Meteor Society event number 1192 for 2012.

Learn more about Park Forest, Illinois

Park Forest, Illinois

March 26, 2003

This meteorite fall, which was one of the largest recorded to date, was reported as very bright and produced numerous, intense sonic booms throughout the southern suburbs of Chicago, IL.

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