Early in September 2008, members of BIMS were given the opportunity to visit the NHM London. We were hosted by Dr Caroline Smith, Curator of Meteorites, who kindly agreed to allow us behind the scenes access to the national collection. The museum curates some of the most famous and scientifically important meteorites in the world; as with all museums, for reasons of space most of the collection cannot be put on public display. We took a trip into the depths of the building…
The Meteorite Specimens
L’Aigle is an important historical meteorite. Over 3,000 stones fell in a shower in 1803 in Normandy. At that time, there was fierce debate about the origin and nature of meteorites. Following an investigation by the French Academy of Science, they concluded that the combination of physical and witness evidence clearly showed that rocks really did fall from the sky. L’Aigle was a turning point in the understanding of meteorites, although it didn’t completely settle the argument.
Some Very Special Pieces…
Nakhla has several claims to fame. It’s quite a small mass, with only about 10kg known. It was observed to fall in Egypt in 1911, and is alleged to have struck and killed a dog. But most important of all, it’s been shown to be one of the very rare meteorites which originated from Mars.
Note the beautiful shiny, black fusion crust. This forms as the rock heats up and the surface melts in the earth’s atmosphere. Sometimes small ‘rivulets’ of molten rock flow around the surface, and are locked in place when the rock cools. These are called flow lines, and are clearly seen in the photo above.
All our visitors from space don’t crash in sound and fury. Some are so small that they slow down in the atmosphere, and then drift downwards at a leisurely pace, eventually coming to rest on land or sea. If they land in the sea, they accumulate on the sea bed, and someone with a magnet, a microscope, and a high degree of patience can identify and seperate out the extra-terrestrial wheat from the chaff.
This is exactly what was done with material dredged from the sea bed by the Challenger Expedition in the 1870s, and these are some of the original spherules produced by that mission. Incidentally, the space shuttle Challenger was named after ths ship used on the expedition.
This is one of the museum’s newest and proudest acquisitions – the main mass of the CI1 meteorite Ivuna. Ivuna fell in Tanzania in 1938, and represents some of the most primitive material in the solar system. Only 700g was ever recovered. The museum paid a substantial sum for this specimen, and the story generated strong interest in the national media. (If you’re still looking, it’s the black object between the two white bars! All the rest is temporary packaging designed to maintain a stable, oxygen-free, dry, protective atmosphere until the specimen can be more permanently housed).
Tektites are not meteorites. Most scientists now believe that they are pieces of the earth’s crust which were thrown into space as a result of a meteorite impact. The molten rock solidified as it re-entered the atmosphere, and many of these tektites form into characteristic shapes through rotation or tumbling.
Here are a few from the museum’s collection.
Libyan Desert Glass
Although not strictly considered a tektite, LDG (Libyan desert glass) is believed to have formed in a similar fashion, as a result of an impact or atmospheric explosion turning desert sand into glass. It has long been prized for jewelery. We were shown this particularly nice piece.
LDG is beautiful under normal lighting, but hold it up and illuminate from behind…
…and the delicate texture and inclusions become visible.
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