[message from Marco Langbroek, through Casper]
Hi Ed, Bob and others,
(my computer crashed recently and due to this my e-mail is down; hence a
reply through Casper's address).
Ed bombarded me as expert on cosmic dust particles in a recent mail ;-)
Indeed I did some work in this field; recovering (succesfully) cosmic
spherules from 400 000 yrs old sediment from an archaeological excavation.
Analysis at the UNM showed at least one of these to be genuine. So at least
I've seen these things and some experience with searching them under the
microscope. Would not consider me an expert though. But I do have a few
things to say;
Unfortunately, much of the magnetic particles to be collected with a
collector on rooftop-level will probably not be meteoritic. As Ed
rightfully remarkes, industrial waste products will among them, and
magnetic spherulic particles are a known form of these. In addition, smal
magnetite crystals which form a, often abundant, natural component of
soils, undoubtedly will be among them. I actually feel that with such an
experiment (collecting with a rooftop collector), it is most likely that
the vast majority of magnetic particles collected will NOT be meteoric dust
particles at all. In my own experiment I used a sediment sample collected
from a sealed (and thus pristine) level predating (considerably - by 400
000 years) the onset of any form of industrial pollution. And even there, I
found (after many evenings of searching behind the micro, and after first
using a magnetic separation technique to extract the magnetic particles)
only a handfull of possible cosmic spherules, picked out from uncountable
quantities of clearly non-meteoric particles, mostly magnetite grains. (the
search image was for perfect spherules, as these are not likely to be
natural terrestrial products although even here one has to be carefull.
magntite grains from soils have a cristal appearance, although this is not
always clearly apparent. Industrial pollution however can be almost
perfectly spherulic too).
Thus, the remark from the old newspaper quoted, especially the second half,
that: "Almost all the meteor dust in the bucket will contain iron; other
particles will not. Thus any grains picked up by a magnet can be safely
assumed to be meteor dust" is certainly not correct, as there are many
magentic particles airborne usually that have not to do with meteorites
altogether: not only the industrial waste products, but also magnetic soil
particles blown about.
If you want to find meteoric dust, the best thing to do is try your hands
at a sample which is likely pristine and predating the onset of industrial
pollution. This is one reason (the other is connected to maximizing
collection surfaces) why scientists in this field often turn to searching
in samples of antarctic or glacier ice, or deep sea sediment cores.
Hope I did not spoil anyones believes, but I have seen these kind of
experiments of "collect cosmic particles yourself on your rooftop!" seen
advertized many times in articles or internet pages, often even as proposed
highschool or primary school science class experiments; and I do not
believe their optimism. I think the picture these paint of the chance of
success and the level of certainty that what you collect is meteoritic
dust, are much, much too optimistic.
Happy 2003 to all,
Casper ter Kuile, Dutch Meteor Society (DMS)
Akker 145, NL-3732 XD, De Bilt, The Netherlands
Private E-mail: casper.ter.kuile@...
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