Meteorite fall statistics
Encyclopedia
Meteorite fall statistics are frequently used by planetary scientists to approximate the true flux of meteorites on the Earth. Meteorite falls
are those meteorites that are collected after being witnessed to fall, whereas meteorite finds are discovered at a later time. Although there are 30x more finds than falls, their raw distribution of types does not accurately reflect what falls to Earth. The reasons for this include:
There have been many attempts to correct statistical analyses of meteorite finds for some of these effects, especially to estimate the frequency with which rare meteorite types fall. For example there are over 100 known lunar meteorite
finds, but none has ever been observed to fall. However, for abundant types, meteorite fall statistics are generally preferred.
These statistics are current through June 27, 2011.
) is into irons, stony-irons, and two major groups of stony meteorites, chondrite
s and achondrite
s. For some of the less-studied stony meteorite falls, it is not known whether the object is chondritic; thus the number of meteorites that can be so grouped is 4% lower than shown above. These numbers are shown in the next table. One could make a slight correction for the undercounting of stony meteorites (e.g., the percentage of irons would decrease by a 0.2%), but this was not done.
Meteorite falls
Meteorite falls, also called observed falls, are those meteorites that were witnessed by people or automated devices as they moved through the atmosphere or hit the Earth, and were subsequently collected. All other meteorites are called "finds"...
are those meteorites that are collected after being witnessed to fall, whereas meteorite finds are discovered at a later time. Although there are 30x more finds than falls, their raw distribution of types does not accurately reflect what falls to Earth. The reasons for this include:
- Some meteorite types are easier to find than others
- Some meteorite types are degraded by weatheringWeatheringWeathering is the breaking down of rocks, soils and minerals as well as artificial materials through contact with the Earth's atmosphere, biota and waters...
more quickly than others - Some meteorites, especially iron meteoriteIron meteoriteIron meteorites are meteorites that consist overwhelmingly of nickel-iron alloys. The metal taken from these meteorites is known as meteoric iron and was one of the earliest sources of usable iron available to humans.-Occurrence:...
s, may have been collected by people in the past who recognized them as being unusual and/or useful, thereby removing them from the scientific record - Many meteorites fall as showers of many stones, but when they are collected long after the event it may be difficult to tell which ones were part of the same fall
- Many meteorites are found by people who sell meteorites... valuable, rare types become known to science quickly, while those of low value may never be described.
There have been many attempts to correct statistical analyses of meteorite finds for some of these effects, especially to estimate the frequency with which rare meteorite types fall. For example there are over 100 known lunar meteorite
Lunar meteorite
A Lunar meteorite is a meteorite that is known to have originated on the Moon.-Discovery:In January 1982, John Schutt, leading an expedition in Antarctica for the ANSMET program, found a meteorite that he recognized to be unusual...
finds, but none has ever been observed to fall. However, for abundant types, meteorite fall statistics are generally preferred.
These statistics are current through June 27, 2011.
Statistics by material
For most meteorite falls, even those that occurred long ago or for which material has never received complete scientific characterization, it is known whether the object was a stone, stony iron, or iron meteorite. Here are the numbers and percentages of each type, based on literature data.Material | Number | % |
---|---|---|
Iron meteorites | 49 | 4.5% |
Stony-iron meteorites | 11 | 1.0% |
Stony meteorites | 1036 | 94.5% |
Total | 1096 | 100.0% |
Statistics by major category
The traditional way of subdividing meteorites (see Meteorites classificationMeteorites classification
The ultimate goal of meteorite classification is to group all meteorite specimens that share a common origin on a single, identifiable parent body. This could be a planet, asteroid, Moon, or other current Solar System object, or one that existed some time in the past...
) is into irons, stony-irons, and two major groups of stony meteorites, chondrite
Chondrite
Chondrites are stony meteorites that have not been modified due to melting or differentiation of the parent body. They formed when various types of dust and small grains that were present in the early solar system accreted to form primitive asteroids...
s and achondrite
Achondrite
An achondrite is a stony meteorite that does not contain chondrules. It consists of material similar to terrestrial basalts or plutonic rocks and has been differentiated and reprocessed to a lesser or greater degree due to melting and recrystallization on or within meteorite parent bodies...
s. For some of the less-studied stony meteorite falls, it is not known whether the object is chondritic; thus the number of meteorites that can be so grouped is 4% lower than shown above. These numbers are shown in the next table. One could make a slight correction for the undercounting of stony meteorites (e.g., the percentage of irons would decrease by a 0.2%), but this was not done.
Category | Number | % |
---|---|---|
Irons | 49 | 4.6% |
Stony irons | 11 | 1.0% |
Achondrites | 85 | 8.1% |
Chondrites | 910 | 86.3% |
Total | 1055 | 100.0% |
Statistics by meteorite group
Probably the most useful statistical breakdown of meteorite falls is by group, which is the fundamental way that meteorites are classified. About 5% of the meteorites in the table just above have not been sufficiently classified to allow them to be put into such groups. Again, a small adjustment could be made to the percentages to correct for this effect, but it does not greatly change the results. Note that a number of meteorite groups are only represented by a small number of falls; the percentages of falls belonging to these groups have a large uncertainty.
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Grand Total: 996 meteorites |
Statistics by Country
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Grand Total: 1096 meteorites |
Statistics by Continent and Time
Epoch | Europe | Asia | North America | Africa | South America | Oceania | Total |
---|---|---|---|---|---|---|---|
Pre-1400 | 1 | 1 | 2 | ||||
15th century | 4 | 4 | |||||
16th century | 2 | 2 | |||||
17th century | 9 | 3 | 12 | ||||
18th century | 25 | 3 | 28 | ||||
1800–1820 | 31 | 7 | 3 | 1 | 42 | ||
1821–1840 | 26 | 11 | 9 | 1 | 1 | 48 | |
1841–1860 | 42 | 15 | 12 | 1 | 70 | ||
1861–1880 | 47 | 36 | 14 | 6 | 4 | 1 | 108 |
1881–1900 | 36 | 27 | 20 | 7 | 2 | 92 | |
1901–1920 | 26 | 55 | 21 | 10 | 4 | 2 | 118 |
1921–1940 | 38 | 55 | 32 | 17 | 14 | 5 | 161 |
1941–1960 | 27 | 27 | 18 | 31 | 12 | 3 | 118 |
1961–1980 | 19 | 42 | 22 | 29 | 8 | 3 | 123 |
1981–2000 | 12 | 49 | 19 | 24 | 4 | 2 | 110 |
2001- | 10 | 14 | 11 | 15 | 6 | 2 | 58 |
Total | 355 | 345 | 181 | 142 | 53 | 20 | 1096 |