"That trap door!" Tom exclaimed. "It leads to a mine. Miles and Brett have discovered high-grade uranium right here on Titan where everyone thought there was nothing but crystal!"
Astro nodded grimly. "And that isn't all. This room is free of ammonia gas."
"But how in the star-blazing dickens can they keep it out of here when everything else outside is flooded with it?" asked Tom.
Astro spun around and began to examine the walls. "Just as I thought!" he exclaimed. "This room is airtight! Sealed! Oxygen is being pumped in here."
"From where?"
"Might be from somewhere below," replied the big Venusian. "Down that trap where Miles and Brett went."
Tom put his mask back on and headed for the door. Astro followed him. They opened it a little and peered into the swirling mist.
"Then it's being pumped in directly," Tom asserted. "Through a duct leading directly up into this room from somewhere below."
Astro nodded. "Then there's only one thing left to do. Go down through that trap door and see what we can find." He stepped forward.
"Wait a minute, Astro," said Tom, stopping him. "Let me check our oxygen. There might not be any down there. Remember, Miles and Brett wore their masks."