Boo! That was all to quick for my liking. I was hoping there would be at least a few days of theorising.
Phil Plait over at Bad Astronomy guessed that it was a rocket spinning out of control:
However, after a moment, I realized this must be a rocket, most likely spiraling out of control. I don’t understand all the details — I don’t have all the info yet — but a rocket fits what we’re seeing here. First, this was seen all over Norway, so it must have been at a high altitude to be so visible. Second, the blue spiral angling down to the right is clearly due to perspective. A rocket spiraling around, and coming up from the lower right, would appear to make tight spirals when it was far away and bigger ones as it got closer.
Plait goes on to give a bunch of other reasons why it must be a rocket. And then he updated the post with this video made some time ago of a model of what a rocket going out of control would look like. I’m declaring the mystery solved. (The model even predicts the weird cone-shape beam of light coming out of the centre of the spiral.)
We’ll see if we can still milk some crazy alien theories out of the media.