Just how did the alien control the ship by essentially touching vacuum was beyond Carthus’s comprehension. The air rapidly flooded into the room, returning sound to the equation. Once the air pressure stabilised on a tolerable, albeit low level, Carthus gestured to his men, fingers forming a closed fist with the thumb jutting up, and switched the suit to open-circuit breathing, taking a deep breath of the oxygen-rich atmosphere.

When he turned back to the alien, his helmet - or her helmet, or its helmet as far as he knew -  was off and it spoke, in a truly alien language. It sounded vaguely like the time one of his brothers tried to speak with his tongue under local anesthesia. [i]“Well, this ought to be interesting, but at least we’re getting somewhere.”[/i] he thought. At least it could talk, that was a step ahead.
“Greetings.” he responded and took off his helmet, unaware of what the alien said, but this seemed to be an appropriate thing to go for. He let go of the helmet, letting it float beside him to illustrate that enabling gravity might be a good next step. He wasn’t too worried the gravity these people were used to would be too much to handle. If their natural gravity was so high it would pose major problems, they were not likely to subject themselves to zero G environments for this long.
“Perhaps you could do something about this, if you’d be so kind?” the Primarch said, pointing at his floating helmet, hoping the alien would get what he meant.