Why does the ship from Prometheus look just like the ship from Serenity?

As I mentioned yesterday in my super awesome Avengers review, the trailer for the Alien prequel Prometheus was shown in advance of the movie, along with other sci-fi and comic book films like The Dark Knight Rises and Amazing Spider-Man (the Battleship trailer might have also played, but I tend to put all instances of that abomination out of my head, so I can't be sure).  It was the first time I had seen the trailer after hearing a little bit of chatter about the movie.  What I saw, seconds into the showing, really threw me for a loop, as lo and behold, Serenity, the wonderfully designed ship from Firefly and the followup movie, Serenity, descended upon some alien world.

"This is it," I thought for the most fleeting of moments, "a new Serenity movie that I've been longing for these many years."  My thoughts quickly turned, then, to something akin to "Wait, how have I not heard about this before right now?", and finally to "This isn't a new Serenity movie!  WHO WOULD PULL SUCH A CRUEL, HEARTLESS JOKE ON ME?!?"

It seems to me that the ship from Prometheus looks a heck of a lot like Serenity.  Enough that it made my heart skip a beat at first glance.  I took a few images from the Internets and Photoshopped 'em together to illustrate my point.  In each instance, the Prometheus ship is on the left, and Serenity is on the right.

I'll admit that I'm not the most impartial judge in this regard.  Firefly is, without a doubt, one of the best shows to grace television sets, and Serenity was a faithful, beautiful adaptation and continuation.  What Joss Whedon put together in one brief season plus a feature movie was nothing short of a masterpiece.  So when I see something remarkably similar to the iconic ship from the show in another movie, I take notice.

It must be said that Whedon and the Alien franchise are not without their connections.  Whedon was one of the writers on Alien: Resurrection, though I don't believe he had a leading voice in that film's direction.  I will also say that I'm not the most familiar with the Alien movies in their different incarnations.  Even so, it seems like this similarity is the result of one of three things:

1) The ship from Prometheus is a blatant ripoff of Serenity.
2) The ship from Prometheus looks like Serenity as a loving tribute to Whedon and his contribution to Alien lore and sci-fi in general.
3) This is all a big coincidence.

Chances are, I understand, that choice #3 is the most likely, but wow!  What a coincidence if that's so!  I realize that there are only so many ways of designing a science fiction space ship, but I wish that there was at least a little more distinction than there is.

Of course, this could all be remedied in one fell swoop by simply renewing Firefly or making another Serenity movie.  Come on, Hollywood.  Make this happen.  I said do it!