Ultraviolet Hubble Movie

If I had to guess, I would say the source are aurorae at the north pole of Jupiter.

According to the labels, what we see is a transit of Europa. Europa is a moon on Jupiter and circling it clockwise. In the video, it is visibly moving from 'left' to 'right', so we are looking at the north pole (the dark spot is the shadow, the faint circle to the bottom and right is the moon itself (this was mixed up before, thanks to haiguise for catching it)).

Here is a what looks like to be a real color image overlayed with an UV image in blue-ish colors:

https://en.wikipedia.org/wiki/Jupiter#/media/File:Hubble_Cap...

Edit: it even says "Jupiter" on the label of the last image.