[meteorite-list] Brownlees in Rainwater

[Chris Peterson]

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" <francisgraham at rocketmail.com>
To: <meteorite-list at meteoritecentral.com>
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