The Stardust aerogel contains small "inclusions" - that is, little pieces of dust that were
introduced when the aerogel was manufactured. (Every effort was made to keep the aerogel clean when
it was made, but some contamination is unavoidable.) This is an example of a field of view with a small
inclusion, just at the bottom of the focus range. Notice that it is not associated with a track.
If you look carefully, you'll find a second one in this movie. Please ignore inclusions.
Move the mouse cursor across the blue bars to change focus.