The Layer of Mist Covering the Eggs

how bout that, preserving the eggs most like

That's one of the oddest mysteries in Alien. The egg cavern shouldn't physically fit in the juggernaut. Kane even calls it a "Cave of some sort," but it's never clarified if it's a cave under the thing or not.

Production-wise, I think originally the eggs were supposed to be just surrounded by dry ice vapor, but if I'm not mistaken, the laser beam was a new gimmick in music shows, which they brought in for extra effect. Good call because it looks great -- even today.

As to what its plot function is, I would agree that it provides some care and protection, but would also suggest it provides a means of warning when anything has approached too close to the eggs (ergo trigger a hatching), in the form of a sound, when Kane broke the beam with his hand.

Final point on the egg chamber size: it wasn't originally meant to be in the Derelict (I for one, still prefer to believe it isn't, and instead is an underground cavern beneath the Derelict). Instead, it was supposed to be the inside of the pyramid, as described in the original screenplay. But they ran out of money. Apologies if all y'all knew all of that already.

@Stan

I agree about the chamber size. When comparing the scales of the chamber and derelict, the Derelict looks too small to me.

"I am now thinking that the mist was a protective cover set by the SJ's so that if an egg hatched during delivery to another world they would be alerted."

That's what I've always thought it was.

As for the size of the Derelict - until we get a look at it as a whole, the egg chamber is simply below ground level.

it definitely points to the fact that someone knew they were there, the eggs were arranged in a fairly organised fashion  so the mist, due to the eggs occupants nature, could very well be something to aid preserve the eggs for long spells. it def looks more like a cave than part of the ship though the shape of the cave would suggest the same shape as the ship but i don't see the point in having such a huge room to store and transport eggs if it is indeed intended to be the derelict

The laser mist being an alarm to the jockey is a good theory, but I see it as an advanced tripwire that would cause the awakening of dormant facehuggers.

This isn't the case in the sequels because Cameron and the other directors probably had completely different ideas as to their origin and function, with the Alien Queen being the source of the eggs instead.

This is one of the reasons why Alien is my favourite, it goes deeper with all the mystery but doesn't make everything into a mess.

As for the Nostromo crew, I'm not sure they descend into a cavern below the derelict though, as Ridley has stated in a "making of Alien" video and also in the recent BAFTA interview that he believed that the Derelict was a cargo ship and the eggs being the deadly cargo of biological weapons to wipe out life, but that doesn't disregard the fact that it still may be a cavern that houses the eggs and where they are loaded from.

not sure about the warning theory or that the breaking of the mist would awaken the dormant facehugger tho good theories. remember kane passes very close to several eggs (even knocking one over when he slips lol sure that wasn't meant tho) and none open, the first sign of movement is after he touches the egg, I think... plus I don't think the facehugger is designed for chasing tho it has been shown in other films theyr berfectly suited to do so, but the legs/fingers are meant for grasping and the tail designed to wrap around something such as kanes throat, which makes me think the mist is for preserving the eggs and the facehugger is only alerted to movement when something is in striking ranges

Ok now I seriously have to see Kane knocking a Xeno egg over XD that sounds absolutely hilarious!

(How did I miss this detail...)

if I am right, haven't seen alien in a while, he does knock one over when he falls off the 'wall' and down into where the eggs r, I might be wrong about it but im sure one gets knocked over or at least he knocks into one when he falls

Giger must've been furious! 

I feel like the laser/fog maintained the atmosphere of the eggs so they would stay undisturbed during transport. Obviously, the moment Kane falls in the atmosphere changes and the face hugger senses heat/prey and..well, you know the rest.