Meteorite

Our sampling of meteorites is strange and not statistically representative, because of the ways in which they are most frequently found. Numerous metallic meteorites are found with metal detectors by collectors, while the more common stony meteorites are remarkably difficult to distinguish from ordinary rocks without training.

Numerous meteorites of scientific interest are found in Antarctica, for several reasons:

1. Ice flow concentrates the meteorites over millions of years in locations where ice melts or sublimates
2. Biological contamination of the meteorites and chemical weathering are both minimized
3. Less distinctive types of meteorites can easily be found, such as Martian and lunar meteorites.

The National Science Foundation funds an annual expedition to Antarctica for meteorite collection, basically a batch of graduate students that cruise around on snowmobiles looking for anything that isn't white.

(Suggestions/insults very welcome. My very first post ever, somewhat tentative, and largely experimental.)

A particle from space that has fallen to the earth.

To improve on the Webster 1913 definition I'd like to mention that the word meteorite is not interchangeable with meteor or meteoroid.

A meteoroid is moving in space. It becomes a meteor if it enters the Earth's atmosphere.

A meteor only becomes a meteorite if it survives the fast and fiery trip through the atmosphere and comes to rest on or impacts the Earth's surface. Of course it has to be found and identified by someone too, otherwise, it's just a rock.

Earth has been visited by meteorites many times. More than 140 meteorite craters demonstrate that. These scars are usually thousands or millions of years old. The most famous one is the Barringer crater in Arizona (age 40,000, size 1200 meters, depth 180 meters). South Africa owns the oldest dated meteorite hole on Earth. The Vredefort crater spans 140 kilometres and is almost 2,000,000,000 years old.

Regarding the earth's age, the number of craters seems quite low. But many impacts have already faded away or are invisibly hidden on the bottom of the ocean. Extra-large bangs are really exclusive however. The most striking that we know of is that of 65 million years ago, when the dinosaurs became extinct. A 10 kilometres wide planetoid crashed onto earth, causing a collision comparable to an explosion of hundreds of nuclear bombs. Off the Yucatan coast (Mexico) a 180-km crater was formed. Dust and vapour formed a veil around the Earth, blocking out the sunlight. Most plants and animals died. No more than twenty percent of all life forms on Earth survived, including some small mammals, among which the predecessors of the human race.

These disastrous impacts are very rare. Scientists have calculated that rocks of this size collide with earth once every 100 million to 1 billion years. The smaller ones however seem to visit our region more often. For example on December 9, 1994: a meteoroid with the size of a house neared our planet at 100,000 kilometres. This seems a lot, but astronomically speaking you could feel the wind while it was passing. On crashing with earth, this rock would have caused an impact almost similar to the Hiroshima bomb.

On October 26, 2028, the near-Earth asteroid 1997 XF11 will make a close approach to our planet. Initial reports indicated an extremely close passage. At that time the error margin was still so large that an impact could be possible. The current analyses predict an approach distance of 0.00636 AU (951,000 km) or about 2.5 times farther than the moon. The probability that the asteroid will impact the Earth is effectively zero.

• If you ever hear a report from a person who claims a meteorite fell to the ground, and he touched it and burnt his finger on the rock, you will know the testimony is a fib, because freshly fallen meteorites are cold. In fact, meteorites often become frosty due to contact with the moisture in the air.

• I thought this was very scientific and pretty, I love it when science and poetry combine: You have tiny meteorites in your hair. We all do. They are micrometeorites and they are therefore only visible through a microscope, but these tiny particles rain down upon earth continuously. They are buried in all the dust and dandruff and pollen and smog in your hair though, so you can’t detect them without advanced laboratory equipment, but nevertheless, they are there. I feel cosmic just touching my hair now, I almost expect it to start glittering and glowing, and growing its own galaxy.

Me"te*or*ite (?), n. [Cf. F. m'et'eorite.] Min.

A mass of stone or iron which has fallen to the earth from space; an aerolite.

Meteorites usually show a pitted surface with a fused crust, caused by the heat developed in their rapid passage through the earth's atmosphere. A meteorite may consist: 1. Of metallic iron, alloyed with a small percentage of nickel (meteoric iron, holosiderite). When etched this usually exhibits peculiar crystalline figures, called Widmanstatten figures. 2. Of a cellular mass of iron with imbedded silicates (mesosiderite or siderolite). 3. Of a stony mass of silicates with little iron (meteoric stone, sporadosiderite). 4. Of a mass without iron (asiderite). <-- Comm: carbonaceous? Add mark for composition? -->

 

© Webster 1913.