These photos claim to show some kind of circular craft spraying a trail.
But what we seem to have here it's a very bright reflection off a shiny curved spot on the plane, and it's slightly out of focus. The unfocussed highlight reflection is know as "bokeh", and this can be much bigger than the actual object, depending on the degree of focus.
Here's a demonstration with a reflection off a car. Only the focus is changed, not the zoom:
To more closely replicate the effect, I set up a very bright flashlight, and pointed it a steel rule, with a small round magnet at the end. The round magnet would simulate the curved surfaces of the plane, and give a nice highlight.
I then took photos of this at various focus levels. Again there is no zoom here, only the focus is changing.
If we adjust the contrast like in the "UFO" photos we see a similar ring around the out of focus highlight:
Here's the first and last frames overlaid, so you can see how big the bokeh is relative to the highlight.
[This posted was updated Sep 1 2014]
( Gif by @Trailspotter https://www.metabunk.org/explained-...rail-and-motion-blur.t8284/page-2#post-198134 )