Location: Chemistry/Physics Building, MUN
Time: 8:00 pm
Garry introduced everyone and also mentioned some facts about the RASC. His laptop was playing a presentation with some facts on the RASC. Robert Babb passed around a sheet for anyone to sign who was interested in observing.
A good number of people had seen things this month, including some visitors. Fred managed to see the triple conjunction. Tim Caruk has been busy taking pictures. Finally, Jim Gillard and Simon Dawson have seen a few things from Jim's observatory.
Member Phil McCausland has been working at the University of Western Ontario. Home for the Christmas break, he has graciously agreed to keep us up to date with his activities. Mainly, he has been characterising various meteorites, including non-destructive tests of structure and composition. He has been playing with a number of interesting meteorites, and also some unknown samples. A collection of types was also shown later.
A large number of the meteorites Phil has been working with have come from a private collector, David Gregory. He has worked also with Dr. Roberta Fleming, present at the meeting, and used some of her equipment.
Phil wanted to give us a flavour of the various kind of meteorites, so he showed us some different kinds, starting with the famed Tagish Lake C2 Chondrite. Some of the distinguishing characteristics often include a fusion crust and 40 micron glass beads.
Phil worked to get data on these samples, including mass, volume, density, and porosity. He described how he uses helium pycnometry to find the porosity -- the helium starts in one chamber and is released into another with a sample of known volume. Using Roberta's micro X-ray diffraction equipment, he can determine any crystal structure. Phil showed us the setup for this in the laboratory.
Meteorite classification has changed somewhat in recent years, with a division into irons, stony-iron, and stony types coming into favour. We got to see how these types are further sub-classified, and the origins of the different types was expanded upon. A typical meteor may contain constituents from the primordial solar nebula, early parent bodies, and current planets and asteroids. Meteorites can be classified as differentiated or undifferentiated, depending upon whether their material has been processed by heat due to an origin in a sufficiently large body (self-gravitation and Al-26 radioactivity versus volume determine if enough heat is generated). Meteorites with an "H" designation have been processed. H3 to H1 indicates water processing, and H4 to H6 indicates thermal processing. Phil showed some classification schemes, which have become somewhat confusing, thanks to historical reasons.
Up to this point, the production of meteorites was discussed. Phil now turned to the problem of how they end up on earth. He discussed Kirkwood gaps and the influence of Jupiter in the asteroid belt. There are less than 10 meteorites where we have reconstructed their orbits, but they confirm these ideas.
Some examples of well known meteorites of the major types were shown, including the carbonaceous chondrites: Allende, Murchison, and of course, Tagish Lake. The Dresden meteorite, the largest chunk being excavated by Dan Solomon was discussed, including a bit on the history of this Ontario fall (there was a Journal article on this recently). Recently, UWO honored Dan's descendants with a small piece of the meteorite and a scholarship. We saw some example of Vesta fragments, bits of Mars, and the Moon.
Phil finished with a discussion of a few meteorites that UWO is trying to characterise. Some were pretty strange in appearance. Others they were trying to determine an origin -- they appeared somewhat similar to other samples of already known origin. We got a flavour of some of the difficulties in studying these meteorites and determining origins.
Robert passed around a handout, and briefly covered the sky for next month. Basically: Saturn, 2 meteor showers, and 4 comets, with one comet being a decent target for binoculars.
Randy has finished a generic poster to attract people to our meetings. He is asking for people to help him spread it around town.
We also got to see some meteorite samples up close.
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