Hi Francis-
I've never seen anything that conclusively identified particles
recovered in this way as being micrometeorites. It is nearly certain
that the vast majority of such particles are not, however. Something I
read recently found that microscopic melted iron particles are produced
in copious volumes by all sorts of industrial processes, and these
particles are wide spread.
That said, I think the exercise of collecting and studying such
particles remains an excellent science project for high school and
middle school students. Undoubtedly there are micrometeorites, even if
conclusively identifying them is difficult. We do this in the classroom,
and have found a few odd particles over the years. The ones I would be
most inclined to think are micrometeorites are, in fact, not magnetic at
all. (We collect on filters, not magnets.)
Chris
*****************************************
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
----- Original Message -----
From: "Francis Graham" <[EMAIL PROTECTED]>
To: <[email protected]>
Sent: Tuesday, November 20, 2007 7:31 AM
Subject: [meteorite-list] Brownlees in Rainwater
Dear List
I have a question which has been vexing me for some
years.
I was introduced to a method of collection of
micrometeorites by Larry Megahan some years ago, which
consisted of collecting rainwater and then wrapping a
powerful rare Earth magnet in Saran (TM)wrap. Placing
the Saran wrap on a glass plate, and examining it
under the microscope, one could see many ferromagnetic
particles. Some were rounded and ablated and it was a
strong guess that these were micrometeorites.
I have had some students try this project and indeed
some of the particles are microspheroids of ablated
iron, similar to so called "Brownlee particles"
colected in the stratosphere.
But I have reason to be suspicious, especially if
the collection is near a former industrial or mining
site.
MY QUESTION IS, has this method, widely circulated
in presecondary teaching circles, ever been critically
evaluated by electron microprobe analysis, X-Ray
fluorescence or some such?
And at what size level does a meteorite cease to be
of interest?
It would naively seem, that although a very very
very tiny percentage of meteorites are lunars or
Martians, if a way to rapidly identify micrometeorites
can be done, a lot more information on Mars and the
Moon could be obtained, simply because there are so
many micrometeorites. This would include collection in
the stratosphere as Brownlee did, maybe piggybacked on
surveillance aircraft.
But one question at a time.
Francis Graham
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