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Re: (meteorobs) Amateur micrometeorite hunters pictures

----- Original Message -----
From: "Jim" <sunwatt@starbanddot net>
Sent: Sunday, December 16, 2001 12:46 AM

> This material was collected where the rain washes off my roof, with a
> small magnet inside a ziplock bag. I have no idea if I found any
> micrometeorites yet.
>
> Maybe someone can have a look and give me their opinion.

Dear Jim,

First, let me point out that I am very positive to your experiment. But I am
affraid that I think that the particles you show are terrestrial soil
particles. Soil particles often contain magnetite and hence are attracted to
a magnet. The morphology and structure of the particles on your photograph
does not match those for micrometeorites, which generally are spherical or
subspherical. Admittedly, my own experience is with true spherules (the most
common type of microscopic meteorite material), but my assesment in this
case was underlined by a comment I asked from the IDP expert at UNM with
which I collaborate. I am myself involved in the search for cosmic
spherules: I've recovered spherules from 400 000 year old sediments from an
archaeological dig in the Schoeningen quarry, Germany. It took me several
weeks sifting through the <0.5 mm fraction of sieving residues of a very
large amount of sediment to find only a handfull of spherules.
The problem with catching airborn particles at rooftop level is that you
also catch a lot of man-made pollution (and soilparticles), which sometimes
travel far by the way, in that way. Some of those mimmic MM's and spherules,
and sometimes you need a SEM analysis to tell the difference. That is why
researchers mostly turn to recovering MM's from more pristine environments,
like polar ice, deep sea sediment cores, or old sealed sediment layers.
A suggestion for the future: inclusion of a scale bar on the
photographs would aid assessment. MM's are typically 20-500 microns, with
most near 200 microns.
The best thing you can do to start with, is concentrate your search effort
on perfectly spherical objects in the given size range. That already rules
out many (but not all) other magnetic particles that are not MM's but which
you can also trap with your magnetic device.

Marco Langbroek

---
Marco Langbroek                    private: marco.langbroek@wanadoodot nl
Leiden University                     work: m.langbroek@arch.leidenunivdot nl
Faculty of Archaeology
P.O. Box 9515
http://home.wanadoodot nl/marco.langbroek/
NL-2300 RA Leiden
The Netherlands
---


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