Catch a Shooting Star
16 FEBRUARY 2020 • SKY & TELESCOPE
the Great Lakes. These samples, though collected far from
industrial centers, nevertheless probably carry some contami-
nants. To improve my chances of picking up a meteorite, I
tend to search along cracks in the rocky river bottom. These
older surfaces act as natural concentration mechanisms for
cosmic dust.
I have also used strong magnets to collect micrometeorites
from the drainage of large parking lots. However, while these
sites do contain tiny space rocks, they also contain numerous
bits of metallic debris from cars. Several large parking lots at
my university are even more complicated strewnfi elds because
students often run metal chop saws there. Too much contam-
ination fi lls the runoff for these sites to be useful.Analysis
I sort my samples by several criteria: A fragment has to be a
magnetic sphere, have a surface melted by passage through
the atmosphere, and be big enough for me to pick up with
tweezers, so that I can place it under an optical microscope.
Since I teach scanning electron microscopy, I also have
access to a number of these microscopes for imaging — which
I admit makes me an unusual meteorite hunter. Under the
microscope, magnetic micrometeorites are fairly easy to spot
by their spherical shape and crystal patterns due to atmo-
spheric wear. If a micrometeorite has sat in the environment
for a while, though, a layer of rust may cover the surface,
which complicates identifi cation.NUT IN A SHELL This 320-micron-
wide micrometeorite has iron and
nickel melted around a grain of
almost pure titanium. (The false color
helps distinguish between these two
components.) While other examples
like this one exist in the literature, the
author considers this to be one of the
strangest samples he has collected.