Canada's latest meteorite - a rare carbonaceous chondrite

Early in the morning of January 18^th of this year residents from all over the Yukon, and from adjacent parts of Alaska and B.C., witnessed a spectacular fire-ball streaking through the sky towards the south. Not only was it an impressive sight, but many people report having heard it, and even smelled it! As you may have seen on TV, a trail of dust was visible in the sky for several hours. Estimates based on satellite observations put the diameter at around 15 m - roughly equivalent to a 55 tonne object. It appears to have exploded at an altitude of around 20 km.

A day or two after the sighting approximately a dozen small pieces of the meteorite were recovered from the surface of a frozen lake in northern B.C. The person who collected them (who wishes his name and location to remain anonymous) must have had some idea of what he was doing, because he placed them into clean plastic bags, surrounded by the snow in which he found them, and took them straight to his freezer. They were then sent still frozen to the University of Calgary, and eventually to NASA's Johnson Space Centre in Houston. One of the first things that NASA did was to make measurements of the gamma-radiation, as this can provide valuable information about the size of the object, and whether the recovered fragments came from near to the centre or near to the edge.

Preliminary examination of the samples shows that the meteorite is a carbonaceous chondrite - a very rare type of stony meteorite (as opposed to "iron" meteorites like "Malaspina") which, as the name implies, are comprised primarily of fine-grained carbon-rich material. A carbonaceous chondrite has not been recovered in over 30 years - the last ones being Murchison in Australia and Allende in Mexico - but this one is especially "cool" because it has been kept frozen and essentially uncontaminated since its arrival on earth. (Although meteorites glow white hot in the atmosphere, it is only the outer part which heats up, and the inner parts stay almost as cool as the extreme cold of interstellar space.) According to a NASA/NRCAN press release the fragments look like "lumps of crumbly rock with a scorched pitted surface - resembling partly used charcoal briquettes: black, porous, fairly light and still smelling of sulphur." The picture shown here comes from the website of Sky and Telescope magazine.

Carbonaceous chondrites are the oldest of all meteorites, with ages that cluster around 4.6 b.y. Since they contain significant amounts of volatile materials, it is assumed that they formed in cool parts of the solar system, and unlike the other stony and iron meteorites, have not undergone much geological modification⁽¹⁾. They are called "chondrites" because they are characterized by many sub-millimetre sized "chondrules" or glassy spheres, which some scientists believe to be "frozen" droplets of some of the solar system's primitive material. Most intriguing of all, however, is the fact that some carbonaceous chondrites have been found to contain protein-related amino acids. As yet not much work has been done on this meteorite, but watch this space for more details! Because of the careful preservation of the recovered specimens, this meteorite may provide us with new and amazing information about the early solar system. What is particularly important is that the samples have been kept cool and sealed up, and hence the loss of the important volatile gases has been kept to a minimum.

The information summarized above comes from the websites of the NASA/NRCAN (National Research Council of Canada) press release and Sky and Telescope magazine, as noted above. Other information is from Dr. Jeremy Tatum of the University of Victoria, from Dr. Richard Herd of NRCAN, and from: Environmental Geology, B. Murck, B. Skinner and S. Porter, John Wiley and Sons, New York, 1996.

1. Most stony meteorites and all iron meteorites are fragments of relatively large objects which have been differentiated -with metallic cores surrounded by silicate-rich "mantles".

Steven Earle, 2000. Return to Earth Science News