Another ship?

Probably a life boat, like described on the Weyland site.

The ship comes up from the ground most likely part of the structure.

That probably just a human outpost building belonging to the humans stationed there. if looked at closely, it looks human made.

Or it a peice of the derelict ship. besides, it too small to be Sj escape pod because SJs are really tall.

....a human escape pod. Described in Weyland timeline.

"Have IQ' just dropped sharply , while I was away?" - Ripley

As in the one ejected from the Prometheus as it chases the Derelict, most likely occupied by Vickers!

There's a larger one too, I think. The scene where Shaw is jumping down to the ground from a smaller ship with a pressure door.

Yes, it appears there was a lifeboat ejecting before the collision. The mercenaries would have to have come with another ship though, but I don't think it was shown. Maybe Shaw is able to escape on the mercenary ship. The big question for me is how does the giant flying saucer fit into the story? It seems to me that in order for the Alien series to logically skip over the idea of visiting the giant alien home world, it would have to have been destroyed.

Why was there no wreckage of the prometheous discovered beside the derelict in Alien then?

could be they were destroyed miles apart from one another and the nostromo crew had little time to discover little else on the planet as they were there to investigate the source of the signal. i think the film will show the reasons why .

In the trailer, the Prometheus is shown crashing into the derelict just above the openings that Dallas, Kane and Lambert entered in Alien. You'd think from that kind of impact you'd see some kind of gaping hole but I see no indication of any damage whatsoever. This is either a different ship or they're going have it 'heal itself'. I doubt Ridley would let a continuity error of that magnitude slip by. [img]http://application.denofgeek.com/images/m/75spaceships/main/derelict.jpg[/img]

Maybe like us they have a fleet of these ships and like you said rick it could be a different ship altogether we shall see. I got a feeling it may not be LV142 at all the landscape is so different to the alien and aliens view of that planet.