What would happen if you opened a jam jar in space?

Answer 1

An interesting question.

Before we get to the act of opening the jar itself, we should probably examine how the closed jar would behave in the space environment to make sure we can actually conduct our experiment as planned!

The first and most glaring difference is that on Earth, the contents of the jar (assuming it hasn't been opened) are at a slightly lower pressure than the surrounding air, but in space the interior pressure of the jar is much higher than the surrounding vacuum. For the sake of this experiment we will assume that the glass of the jar is strong enough so it doesn't shatter and the lid is likewise strong and well secured so it doesn't just pop off before we open it ourselves. Now that we are in no danger of coating the airlock with a delicious mess, let's go outside and open the damn thing.

So now we start unscrewing the lid. If we're careful we can gently let the little bit of air trapped inside the jar escape, lest it pop off and contribute to the growing problem of spa...

...what are you doing? Quick, grab it! I'll try to catch... okay we lost it, it's gone now. Congratulations, you have just created a piece of space debris! Good job! Well, at least the lid is fairly large and made of metal, so it can be tracked with ground radar to make sure it doesn't pose a collision hazard.

Okay what's happening with the jam, now that it's free to enjoy the deadly vacuum of space? Well there's a fair bit of air trapped inside it that wants to get out, so it's probably going to start boiling and expanding out of the jar like a marshmallow. Bits of the jam might flake off, further exacerbating our careless debris pollution of this orbit, but let's assume the jam is sticky enough to stay in one piece. What happens next, it sort of depends. If the jam isn't exposed to the sun it's going to freeze into a bizarre vacuum sculpture after a little while, the thermal stress might fracture the jar as well. I'm not sure what's going to happen if it stays in direct sunlight. It might become vacuum-dried after a while as the water content sublimates. The strong UV radiation is probably going to cause some interesting, if unappetizing chemical reactions. It's probably not going to be recognizable as jam anymore if you leave it outside for longer.

One thing is clear, the result is definitely nothing you'd want to put on your sandwich!