Oh pretty pretty please, Lower Decks! Do it while she's still alive!
Remember the space travel episode where the nerdy kid took off his helmet on Pluto? I'm still a little traumatized.
You may have been mislead...
Pluto has effectively no atmosphere so I think if you're standing on its surface and your boots are well-insulated then you're effectively in a vacuum thermos - you'll actually overheat rather than freeze and taking your helmet off won't make a difference.
(Of course the helmet is still important for breathing... And then later water from your body will gradually boil off into space and cool you that way until you're freeze-dried, but that's not really a concern for living astronauts.)
"Please let this be a normal five-year mission"
"With The Frizz? No way!"
Cruising down on Vulcan, being relaxed and feeling free.
Next that you know it, you see a waahahahoooo Romulans in the galaxy?
That explains Voyager.