So, this trailer actually showed quite a bit. Here we go:
1. We get to SEE the crash of the Derelict Ship. That's just
really cool, since people first caught a glimpse of it in 1979.
2. There's a man in he trailer whose face is undergoing a change. Looks like he turns into this:
3. Now here's where things get ultra interesting. What I think EVERYONE thought was the Pilot-Alien's head is actually a helmet of sorts. (You'll see why I think this in a minute)
4. The Map Room. We see the 'Pilot Chair' rise from this same room during the trailer. NOTE: The person's size here...
5. THE PILOT HIMSELF MAKES AN APPEARANCE! Compare how much bigger he is compared to the human in the picture above. Also, when you see the Pilot-seat rise, there's no head there. (See pic below)
6. See, no head.
Now I wonder why the ship crashes. Until this moment I assumed it was because of The Pilot, er The Space Jockey, got Facehugged or lost control of the ship while a Chestburster tore through him.
So, in Prometheus, the Helmet is taken off the Space Jocket/Pilot. Ultimately it's returned as the crew of the Nostromo find it in
Alien.