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Meteorites

by  Simon Nathan

The incandescent blaze of a shooting star heralds the fall to earth of a small piece of rock from outer space. Known as a meteorite, this fragment from space holds fascinating information about how the solar system was formed. Only a few have been found in New Zealand; one made headlines in 2004 when it crashed through the roof of an Auckland home.


What are meteorites?

Meteorites are pieces of space debris which, having survived a fiery journey through the atmosphere, land on the earth’s surface. They provide much of our knowledge of the origin and evolution of the solar system. Apart from a few kilograms of rock brought back from the moon by astronauts, meteorites are the only material from beyond the earth available for study.

Meteoroid, meteor or meteorite?

A meteoroid is a piece of rock or space debris in our solar system. If it enters the earth’s atmosphere, it becomes visible as a meteor – a bright, moving trail of light, commonly called a ‘shooting star’.

If the object survives its blazing plunge through the atmosphere and lands on the surface of the earth, it is called a meteorite.

What are meteorites made of?

Meteorites are divided into two groups: stony meteorites (stones) and iron meteorites (irons).

Stony meteorites are the most common, and are composed of silicate minerals, similar to volcanic rocks found on earth. Many contain tiny spheres (chondrules), which have been formed by the rapid cooling and solidification of molten droplets. These distinctive stony meteorites are known as chondrites (pronounced ‘kon-drites’). Their chemical composition closely matches that of the sun.

Iron meteorites are heavy and look different from normal rocks, so they tend to be picked out as unusual. They resist weathering, although they are often rusty on the outside. Most iron meteorites contain 7–15% nickel. The curious and distinctive markings revealed by cutting and etching are intergrowths of metal crystals called Widmanstatten structures.

Falls and finds

Meteorites that have been observed landing are classified as falls; those which have been discovered later, on or beneath the earth’s surface, are called finds. Thousands of meteorites land on earth every year, but only five or six are ever found. Meteorites are named after the place where they are found.


Meteorites in New Zealand

Falls

There have been only two recorded meteorite falls in New Zealand, almost 100 years apart.

The Mokoia meteorite

On 26 November 1908 a meteor streaked across the daytime sky, accompanied by a sonic boom. The spectacular event startled onlookers; one witness described the sound as ‘a loud furnace blast’. Two pieces of the meteorite were retrieved from a small crater at Mokoia, in the Taranaki region, and presented to the museum in Whanganui. The Mokoia meteorite is of particular interest because it is one of a rare group that contains compounds of carbon and hydrogen. Along with other carbonaceous chondrites it has been studied in detail, because its so-called ‘organic’ compounds bring scientists closer to understanding the origin of life.

The Ellerslie meteorite

This meteorite crashed through the roof of Brenda and Phil Archer’s home in the Auckland suburb of Ellerslie on 12 June 2004. It bounced off a leather couch and hit the ceiling, before coming to rest on the floor where their grandson had been playing a few minutes earlier. Brenda Archer said that it was lucky it hit the roof: ‘If it had fallen in the garden, it would probably have been added to the pile of rocks I’m taking to the dump. Nobody would have known about it.’ 1

Meteorite spotting

Of the nine meteorites recorded in New Zealand, only two (Mokoia and Ellerslie) have been observed to fall. The others have mainly been found by farmers, who noticed unusual rocks while working in their paddocks.

By comparison, twenty-one meteorites have been found in the United Kingdom. All were observed falls, apart from a single specimen found in an archaeological excavation. It is assumed that the high proportion of sighted falls is due to the UK’s greater population density. But given their greater population, it is surprising there have been so few finds – perhaps New Zealand farmers have sharper eyes.

Finds

Although there have been many searches, only nine confirmed meteorites have been discovered in New Zealand. They were found throughout the country.

Looking for meteorites

It is likely that more meteorites will be discovered in New Zealand. Before any find is accepted as valid, both the specimen and its location are examined by experts, and a sample is chemically analysed. New meteorites are reported to the Meteoritical Society, based in the USA, and a list of finds is published annually.

If you believe you have discovered a meteorite, take it to a museum or university geology department. Because so few have been found in New Zealand, they are of high scientific interest. It is important that they are preserved for future study.

Meteorites discovered in New Zealand are covered by the Antiquities Act 1975, and may not be exported without written permission from the Ministry for Culture and Heritage, which administers the act.

Footnotes
  1. Sunday Star Times, 13 June 2004. › Back

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How to cite this page: Simon Nathan, 'Meteorites', Te Ara - the Encyclopedia of New Zealand, http://www.TeAra.govt.nz/en/meteorites/print (accessed 17 October 2018)

Story by Simon Nathan, published 12 Jun 2006