Sunday, August 28, 2011

Micrometeorite candidates

The kids and I took apart a defective hard drive yesterday, and I used one of the magnets (in a plastic bag, which I then inverted) to fish for micrometeorites in the soil near a downspout.  I found a few plausible candidates, as well as a bunch of surprisingly pretty microscopic ferrous dust. Here is a particularly pretty area.  The pointer is pointing to a round micrometeorite candidate.  It's stuck to some probably earth-origin stuff--the hard drive magnet magnetized all the samples, so they stick together.  There is also a pretty piece of glass or crystal closer to the top edge.

I ended up preparing a slide with four candidates (one a bit dubious) mounted under a glass coverslip.  It's hard to grab pieces as they are very tiny--though big enough to see naked eye as a tiny dot--and stuck magnetically to other things.  In particular, I lost the round one in the first photo, as it just shot away when I tried to grab it with a toothpick (which looked like a big blunt log under the microscope).  Here's one that didn't get away.  It's about 60% of the size of the ball in the first picture.  You can't tell in the photo, but if you shine the light on this, it's very metallic--a nice silvery object. I ended up perfecting a method for extracting them.  First, I use the toothpick to sweep the area around it clean, looking in the microscope most of the time.  It's confusing, since the miscroscope reverses the view, but eventually the brain gets used to it.  Then I wet the toothpick with acetone.  The micrometeorite candidate sticks to the toothpick.  I then transfer it to a clean piece of glass.  Because the acetone evaporates so quickly, it's easy to just wipe the toothpick on the glass and the micrometeorite drops off.  I lost two promising samples--especially that nice big round one in the first photo--before I got the above two.

From what I've read, rounded things that look like they were partly melted are good candidates.  Here is a less rounded one that ended up on the slide of the four that I saved.  I don't know how it got there, as I only intentionally transferred three to it, if memory saves.  Maybe it accidentally got carried there.  It looks too rough-edged to be a micrometeorite.  However, I've also read that they can avoid atmospheric melting by being small, so maybe rough-edged things count as candidates, too.  It, too, has a nice shine to it, though the photo doesn't show it.

If you try to view these with bright-field microscopy, of course you just get black silhouettes.  What I did is I taped a bright LED flashlight to the microscope, pointing at the sample, and then I took timed exposures, holding the camera to the eyepiece (sometimes with some sort of adapter to keep the camera in place).  For the second two photos, I found a way of adding more light.  I took the microscope outdoors, and then reflected sunlight onto the slide with a mirror (actually, a hard drive platter--they make lovely mirrors). The photos were taken with point and shoot cameras hand-held to microscope eyepieces, with some loose-fitting adapters to make it easier. The first photo was with a Sony P100 through the 10X Huygens eyepiece that the microscope came with. The second and third photos were with a Canon G7 through a Rini 30mm telescope eyepiece, using my home-made telescope-to-microscope eyepiece adapter. Update: I wish I knew how to better identify micrometeorites. The very round one may not be one--see this article.

1 comment:

Mark Rogers said...

Dr. Pruss,
I recently saw this and was quite excited. I have been wanting to find a meteorite for a long time. So I put my ten rare earth magnets, that look a lot like the ones you pictured, on a cookie sheet and went trolling over my back lawn for about ten minutes and found four of them! Then I put my micrometeorite trap in an area where the breeze naturally funnels and I captured ten-fifteen in twenty-four hours. I theorized they were naturally occurring particles from the soil. Then I went to a residential construction site where excavation was happening and carefully extracted a hopefully uncontaminated soil sample. I found about one particle per cup of dirt. Then I found one that actually looked like a meteorite! Fusion crust and chondrules and big! I took pictures and sent them to a meteorite authority. He said:

Hi Mark,
I cant help you here. I don't trust any micros not gathered from 
deep polar ice layers. Too much industrial pollution (and even some testing pos for Ni).

Hmm...really? Well it is a lot of fun anyway!