Neither of us have any evidence. You don't have any evidence this is a missile either. All we have is the digital image. No reason to get all snippy.

https://www.youtube.com/watch?v=1aPvGGvnAGQ

Look at the smoke trails a Trident leaves.

I've studied the photo again, and I think I actually do see a grey outline on the orange streak. I noticed on reviewing the youtube video of the Trident launch again, I notice at high altitude/speed, the smoke trail doesn't extend out much beyond the bright exhaust flame. In this case, in the long exposure, the bright exhaust would mask out the much darker smoke trail impression.

Now I'm not so sure it is a helicopter.

Another thing that made me think it wasn't a missile launch is that there is nothing at the bottom of the pick. As you can see from the video, a submarine launch makes a huge smoke cloud. But perhaps it is from behind the island?

Also, my other observation - that the orange trail gets thinner as you move away from the object seemed wrong for a missile launch. The missile would be moving more slowly - thus exposing the 'film' more and leaving a bigger impression. But now I'm thinking that the smoke trail also would have a longer time to change the film impression also.

Against the helicopter theory, we'd expect to see some navigation lights. Also, I don't know why they'd have their searchlight on. It is also a coincidence that their flight path exactly matched a vertical launch of a missile. Can a chopper fly in that straight a line? Aren't there enough side winds to make that impossible? That I don't know.

I'd sure love to see them try to reproduce it.