When a hypervelocity particle hits the aluminum foil, it produces a crater that is typically several times the diameter of the particle. Although these craters are tiny, they are similar in shape and structure to craters on much larger scales, such as these craters on the moon, imaged by LROC:
Here, because the craters we are searching for are so tiny, we are using electron microscopes instead of light microscopes to image the foils.
Here is an example of a crater:
Because the particles stop so quickly, they do not survive capture nearly as well as they do in aerogel. However, in most craters many atoms in the original particle
are retained in the bottom of the craters, and some structure of the original particle can sometimes survive, giving an indication of the morphology and structure
of the captured particle before it hit the foil. In the images that you will search, this material will not be distinguishable from the aluminum foil. Instead, you will look
for the crater itself.
The fields of view that you will be searching are really small, much smaller than the fields of view of the aerogel. The magnification is somewhat variable, but most fields
of view that you will search are only about 20 microns wide. This is only about three times bigger than a red blood cell!
Higher magnification images of craters from The interstellar tray, and three crater-like defects.
We have prepared a tutorial to help you learn how to identify craters and use the VM.
The VM is very easy to use, as you'll see in the next pages.
For the following training tutorial, we have used actual craters found in the Stardust collector.