Part B
Meteorite Basics
There's a lot to learn from studying meteorites, and there are many different online sources of information about meteorites:
> The Meteoritical Society (https://meteoritical.org/) and its meteorite database (https://www.lpi.usra.edu/meteor/)
> The Center for Meteorite Studies at Arizona State University (https://meteorites.asu.edu/)
> The Meteorite Exchange (https://www.meteorite.com/)
> Wikipedia.org (https://en.wikipedia.org/wiki/Meteorite)
> Etc., etc., etc.
We will mainly use information from the Wikipedia web site. A few descriptive articles from Astronomy magazine will supplement the online information. Let's start by reviewing some of the basic information about meteorites.
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Figure 5-3. Stoners and metalheads. On the left is the Allende carbonaceous chondrite (stony meteorite), which fell in northern Mexico in 1969. Note the conspicuous round chondrules and the dark color due to its carbon-rich composition. At right is a fragment of the Canyon Diablo meteorite (iron meteorite), found near Meteor Crater, Arizona. Note the silvery metallic luster and Widmanstätten patterns of this cut and polished specimen. |
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* Do you think you've found a meteorite?*
If so, visit the "How To Identify a Meteorite" web page at the Institute of Meteoritics at the University of New Mexico and find out!
What is a Meteorite?
Meteors and meteorites originate in space as meteoroids, small objects orbiting the Sun that are too small to be classified as asteroids or comets. Most meteoroids are either left-over debris from the early Solar System's disk of dust and gas (the Solar Nebula) or remnants of asteroids that have been blasted apart by collisions with other asteroids or comets. Some metoeroids originated on the surface of larger bodies (planets and moons) and were blown off the surface into space by giant impact processes. In either case, some meteoroids fall into the influence of Earth's gravity field and are drawn toward its surface.
Meteoroids are typically traveling at high velocities (like 20-25 km/s) when they begin to pass through the atmosphere. They are slowed somewhat by friction with the atmosphere, heating up tremendously in the process. The word meteor derives from the Greek meteron (phenomenon in the sky) and describes a streak of light formed as an object heats up and becomes incandescent on its flight through the atmosphere. Most objects completely vaporize during their passage through the atmosphere (meteors), but some survive the journey and impact on the surface as meteorites.
Let's start by going to the Wikipedia Meteorite web page. Read the relevant section and before answering each question.
Falls vs. Finds
Sometimes, the passage of a meteorite is witnessed by people or automated equipment. The meteorite is then searched for, and if found is termed a meteorite fall. Meteorites that are collected, but not witnessed during their passage through the atmosphere are termed meteorite finds and are much more common than meteorite falls.
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Figure 5-4. Meteorite falls and finds. On the left, a meteorite fall that was captured on 16 independent videos and then struck a car in Peeksill, New York. On the right, a meteorite find discovered north of Barstow, California in 2006 whose descent was unwitnessed. |
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Refer again to the Wikipedia Meteorite web page to answer Quiz Me! questions B11 and B12. Read the relevant section and before answering each question.
Types of Meteorites
Meteorites have traditionally been divided into three general groups: stony, iron, and stony-iron.
Stony
> Rocky, composed mostly of silicate minerals.
Iron
> Largely metallic, composed of mostly iron and nickel.
Stony-Iron
> Contain large amounts of both metallic and rocky material.
Modern classification schemes divide meteorites into more detailed groups according to their structure, chemical and isotopic composition, and mineralogy. There are many different meteorite names, but we will only refer to a few of them in this class.
Refer to "Name That Rock", a summary from the Astronomy magazine article "Name That Rock" to answer Quiz Me! questions B13 through B16.
Chondrite Meteorites
Let's look a little more closely at the chondrite meteorites. Refer to the Wikipedia Chondrite web page to answer the next two Quiz Me! questions. Read the relevant section and before answering each question.
Achondrite Meteorites
Let's take a closer look at the achondrite meteorites. Refer to the Wikipedia Achondrite web page to answer the next two Quiz Me! questions. Read the relevant section and before answering each question.
Iron Meteorites
Let's look a little more closely at the iron meteorites. Refer to the Wikipedia Iron meteorite web page to answer the next four Quiz Me! questions. Read the relevant section and before answering each question.
Notable Meteorites
Refer to "Classic Rock", a summary from the Astronomy magazine article "Classic Rock" to answer Quiz Me! questions B25 through B27.
Refer to "Heavy Metal", a summary from the Astronomy magazine article "Heavy Metal" to answer Quiz Me! questions B28 and B29.
Meteorites of Antarctica
ANSMET (ANtarctic Search for METeorites) is a program funded by the Office of Polar Programs of the National Science Foundation that looks for meteorites in Antarctica. All of the material collected by ANSMET is curated for the purpose of research and public education, in contrast to meteorites collected privately, which are frequently sold to collectors.
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Figure 5-5. The ANSMET program. |
Let's visit the ANSMET website and learn more about meteorite research at the bottom of the world. Cruise around this web site and check out all the interesting facets of meteorite research in one of the world's most exotic locations: Antarctica.
Quiz Me! questions B30 through B34 can be answered by going to the FAQ page of the ANSMET web site. Read the relevant section and before answering each question.