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Unmanned Spaceflight.com _ Chit Chat _ Urban micrometeorites

Posted by: marsbug Apr 29 2020, 07:02 PM

Although I realised that it was, in principle, true that micrometeorites are falling all around us, I had always assumed that collecting falling material in hopes of finding some would leave you with a large collection of particles from the local industries. You might, in theory, have a micrometeorite in there but you'd never be able to distinguish it.

However it seems that, with the expertise to identify a micrometeorites properly, and sufficient patience, it is possible. https://pubs.geoscienceworld.org/geology/article-lookup/45/2/119Identification was by way of optical microscope examination first, then by embedding in resin, cutting, and polishing for electron microscope examination and wdx analysis. I don't suppose there's anyone here who has worked in micrometeorite studies who would like to weigh in?

QUOTE

An urban collection of modern-day large micrometeorites: Evidence for variations in the extraterrestrial dust flux through the Quaternary

Abstract
We report the discovery of significant numbers (500) of large micrometeorites (>100 μm) from rooftops in urban areas. The identification of particles as micrometeorites is achieved on the basis of their compositions, mineralogies, and textures. All particles are silicate-dominated (S type) cosmic spherules with subspherical shapes that form by melting during atmospheric entry and consist of quench crystals of magnesian olivine, relict crystals of forsterite, and iron-bearing olivine within glass. Four particles also contain Ni-rich metal-sulfide beads. Bulk compositions are chondritic apart from depletions in the volatile, moderately volatile, and siderophile elements, as observed in micrometeorites from other sources. The reported particles are likely to have fallen on Earth in the past 6 yr and thus represent the youngest large micrometeorites collected to date. The relative abundance ratio of barred olivine to cryptocrystalline spherule types in the urban particles of 1.45 is shown to be higher than a Quaternary average of ∼0.9, suggesting variations in the extraterrestrial dust flux over the past 800 k.y. Changes in the entry velocities of dust caused by quasi-periodic gravitational perturbation during transport to Earth are suggested to be responsible. Variations in cosmic spherule abundance within the geologic column are thus unavoidable and can be a consequence of dust transport as well as major dust production events.:

Posted by: djellison Apr 29 2020, 07:23 PM

The Verge did a great article about hunting for them in NYC
https://www.youtube.com/watch?v=9q3uNcJh4pc

Posted by: bkellysky Apr 30 2020, 12:55 PM

I read about this as a kid, in a Golden Book or somesuch, about putting out a sheet overnight and using a magnet to scoop up the meteoric particles the next day.
Never tried it. I thought local emissions of uncombusted metals from fuels and escaped emissions would be what I would be gathering up.

Posted by: algorithm Apr 30 2020, 06:31 PM

You know, now might be a good time to give it a go. Everyone in lockdown, road traffic and small industrial activity at a really low level.

I have a large garage with a flat roof here in the UK, so when the weather returns to warm days and no wind, I think I'll put a taurpalin over some of it for a few days then get the magnet out. each day.

Great project for the lockdown.

Posted by: marsbug May 1 2020, 12:56 AM

QUOTE (bkellysky @ Apr 30 2020, 01:55 PM)

From what I understand that's true, but if you collect over enough area, over enough time, you'll get some micrometeorites too. The tricky bit is having the knowledge to tell them apart. I'm going to give it a go: We've got plastic guttering, so I'll buy some n52 neodynium magnets and mount them at intervals along it, with a thin removable plastic cover. I'll check them in 6 months or so. To identify any finds I'll have to do lots of lockdown reading on micrometeorites, oh dear oh dear

Posted by: centsworth_II May 1 2020, 05:55 AM

A book by Jon Larsen, http://www.amazon.com/Search-Stardust-Micrometeorites-Terrestrial-Imposters/dp/076035264X has many beautiful pictures of micrometeorites as well as "terrestrial imposters."
Inexpensive for a high quality book.

Edit: Interesting. When I first posted this the book was $7+, now it's $9+. Still a great deal but ... interesting.

Posted by: JRehling May 2 2020, 07:19 AM

Fascinating. I know that the beaches upwind from me contain a fraction of magnetic sand particles (it is easy to fill a cup quickly by pulling them out with a magnet wrapped in plastic), so I would imagine that my locale has a lot more false positives from that than many other locales… I'm not sure how big a source of false positives industry is, and that would also vary tremendously depending upon the location.

For what it's worth, turn on a Geiger counter for about 5 seconds and you'll get something from the cosmos without much effort at all – probably a secondary muon - but it's hard to collect those.