Can Kryptonians breathe in space if they have never been exposed to a yellow sun?

Answer 1

First of all, they don't breathe in space. Even Superman does not breathe in space. There is nothing to breathe in space. The writers are in fact rather inconsistent when it comes to deciding whether superman needs a spacesuit in space, though he has never needed one in the movies. Obviously if Superman can't breathe in space, then Kryptonians without his powers (living under a red sun) can't either. It is, however, sometimes posited that after superman was killed by Doomsday and came back, he can hold his breath indefinitely and does not need to breathe. If this is the case, then I would assume ordinary Kryptonians would die in space just like any human.

Sometimes, it is suggested that the reason Superman can survive in space is that Mongul taught him various breathing exercises while training him, so he can last in space for a VERY long time. Some people also think that Mongul taught him that he did not need to breathe in space as long as he was exposed to enough yellow sun radiation, which would make the answer to your question an obvious no when asking about Kryptonians with no yellow sun exposure.

So, I guess the answer to your question is no whatever way you look at it. Nevertheless, all it takes is another writer to come along and change that to have me eating these words.

Answer 2

No, Kryptonians require exposure to a yellow sun to gain their superpowers, including the ability to breathe in space. Without the yellow sun's radiation, they would not have the same abilities and would be unable to survive in the vacuum of space.