Tom looked at it and then shook his head.

"I haven't seen one of these since I left Venus, and then only when I
was a kid hanging around the spaceports where the space rats used to
blast off for the asteroids looking for uranium."

"You mean you hunt uranium with that thing?" asked Tom.

"No, you dig it out with this."

Tom gazed at the machine thoughtfully. "Why would it be here?" he mused.
"It's already been used," said Astro, standing up. "Look, the drill head
is dull."

"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?"