o one man's suit while we were working, but mostly
they're just a nuisance."

Rip had heard of the creatures. They were like earth armadillos, except
that they were silicon animals and not carbon like those of earth. They
were drawn to oxygen like iron to a magnet, and their diamond hard
tongues, used for drilling rock in order to get the minerals on which they
lived, could drive right through a space suit. Or, if they could work
undetected for a short while, they could drill through the shell of a
space station.

_Scralabus primus_ was the scientific name of the creature, but the fact
that it looked like a silicon armadillo had given it the popular name of
"silly dilly." Apart from its desire for oxygen it was harmless.

Koa reported, "Sir, the block of thorium is ready. We've hung it on a line
behind the landing boat. The blast won't hurt it, and it's too big to get
inside the boat."

"Fine, Koa. Well, Captain, that does it."

The Mercurian Planeteers got into their craft and blasted off, trailing
the block of thorium in their exhaust. Rip watched the cruiser take the
craft and thorium aboard, then drive toward Mercury, brilliant sunlight
reflecting from its sleek sides. The planet was only a short distance away
by spaceship. It was the largest thing in space, except for the sun, as
seen from the asteroid. To Rip it looked about three times the size of the
moon as seen from earth.

Past the orbit of Mercury, the sun side of the asteroid grew dangerously
hot for men in space suits. Rip and the Planeteers stayed in the bitter
cold of the dark side, which ceased to be entirely dark. Even the
temperature rose somewhat. They were close enough to the sun so that the
prominences, great flaming tongues of hydrogen that sped many thousands of
miles into space, gave them light and enough heat to register on Rip's
instruments.

Mercury was left far behind, and earth could not be seen because of the
sun. There was nothing to do now but ride out the rest of the trip as
comfortably as possible until it was time to throw the asteroid into an
ever-tightening series of elliptical orbits around earth, known as braking
ellipses. The method would use earth's gravity to slow them down to the
proper speed. A single atomic bomb and a half dozen tubes of rocket fuel
remained.

Then, as Rip was enjoying the comfort of air during his off-watch hour in
the boat compartment, Koa beat an alarm on the door.

Rip and the Planeteers with