It’s not like he’d fail the bridge officer’s test.

He was clearly a qualified bridge officer. As a member of the regular chain of command (and being the one regularly in charge of the night shift due to not needing to sleep), he had to be. (In fact, he was put in command of another ship once which would have been impossible if he didn't have the qualifications.) In his case it's probably a lack of ambition that led to him being stuck in that rank; he had no real desire to be promoted to another ship when his friends were on the Enterprise and he had every opportunity to learn about meatbags there.

I liked how they explained the red rings around the planet. Water ice with significant iron contaminants would be reddish indeed, though more of a light pink instead of a deep blood red.

Its consequences didn't, though. When you jump into space unprotected, it's not the cold that will kill ya'. Vacuum is the best isolator after all. Water wouldn't condensate on you into frost crystals, it would instantly evaporate because in 0 Pascals the boiling point of water is far below normal body temperature.

What will kill you though, is hypoxia. Also, lung damage if you get blown out into vacuum without warning. Though a: it's still survivable even with 20th century medical attention, and b: given that these were two medical professionals who are working on a spaceship and they knew it was about to happen, they probably knew how to minimize the damage. But the hypoxia is still there.