The importance and relevance of meteorites to Solar System research – past, present and future

Tuesday 20th May, 2014

We were very honoured to have as a speaker Dr Caroline Smith who is Curator of Meteorites at the Natural History Museum in London. Her talk was entitled "The importance and relevance of meteorites to Solar System research — past, present and future" and emphasized how important the study of meteorites was in relation to the understanding of how our Solar System formed.

She began by saying that there were very few reported meteorite finds before the 1800s. Oral aboriginal traditions hinted at them, some North American tribes kept them as sacred objects and Inuits had used them as raw material from which to forge metallic tools. The earliest official record is of a meteorite called "Nogota", which was seen to fall in the night near Nogota (a city in Japan) on 19th May 861 AD. It was recovered in the morning by villagers and has been kept in the Shinto shrine of Suga Jinja ever since.

The person credited with starting the serious study of meteorites, i.e. meteoritics, is Ernst Chladni who was a German physicist and musician. He became very interested in fireballs in the sky and, in 1794, published a book about the "Pallas iron" meteorite suggesting that it was not volcanic in origin but came from outside the Earth. This was highly controversial at the time and it was only later, after the French astronomer Jean-Baptiste Biot had published a report in 1803 regarding meteor shower fragments found in northern France, that Chladni's work was taken seriously.

The modern study of meteorites begins with their collection and transport to laboratories all around the world. The Natural History Museum is one of the most important study centres in the world and it publishes a catalogue of all known "finds". Some of the best areas for finding meteorites are in the deserts of Antarctica or central Australia where the dry conditions allow the samples to remain relatively pristine. The Antarctic is also a popular area since the dark fallen rocks stand out vividly on the white background of snow.

Once the meteorites reach the laboratories they can be examined using the same techniques that geologists use to analyse terrestrial rocks. However, the extraterrestrial samples need to be kept isolated so that they are free from contamination so "clean room" procedures are enacted. Scientists use various tools to analyse the samples including optical, electron and transmission election microscopes. Results from these give an isotopic analysis of a particular specimen which can then be used to tell where the meteorite formed and whether it has undergone any processing.

The "primitive" meteorites are known as "chondrites" and their examination shows the Solar System formed around 4.6 billion years ago from a well-mixed cloud of gas and dust. Parts of the solar nebula were very hot as the chondrites include millimetre-sized spheres that were once molten called "chondrules". The other type of meteorite is known as "differentiated" and these have undergone some form of processing. Differentiated meteorites can be further classified into "achondrites", "stony-iron" and "iron". These can be studied to provide information about bodies such as planets, moons and asteroids formed.