me that the absence of an atmosphere could
answer part of the problem."

Haines nodded. "Let's get to work on a plan of action, men. We've got a
few days to get our equipment laid out."

Those few days passed quickly enough. When several possible schemes had
been outlined, the men made lists of the types of equipment that might
be used with each. Then, putting on pressurized space suits and carrying
air tanks, they left the inner sphere and worked through the cargo space
surrounding it within the outer frame of the spaceship. There had
originally been air here, but now they found most of it was gone,
thinned out from infinitely tiny leaks in the outer shell caused by the
constant bombardment of microscopic bits of meteoric dust.

They located each piece of equipment and moved it into position for easy
handling.

The ship came to its halting point, where the repulsion against the Sun
finally braked it against the gravitational pull of the Sun. Then, by
increasing the selective pull of the approaching planet Mercury, they
moved off in that direction.

Mercury was changing in appearance. As they neared it from the outer
side, its lighted half swung away from their view, and what they saw was
a constantly narrowing crescent, growing larger even as it narrowed.
Finally the hour came when they swung up close, coming in on the
eternally sunless, night side of the little planet.

They swooped low over the dark surface, taking observations and
measurements. "It's not as cold as we might suppose," said Oberfield
after his first readings. "There's a certain amount of heat all along
the rim of the dark side. Radiation, I suppose, as well as the fact that
there's a certain amount of wobbling done by the planet."

Burl was studying the surface. "Seems to me that much of the dark side
has a gleam to it. Something reflects the stars; I see little glints of
light, shifting and blinking."

"I can guess what that is," said Russ. "It must be covered, at least in
the central portions, with a sea of frozen gases. What atmosphere
Mercury had long ago must have congealed there."

The ship moved along toward the twilight edge, then began circling the
planet along that intermediate belt, where the Sun could be seen peeking
over the horizon in eternal dawn. There was a cluster of men at the
radiation counter, looking for evidence of the Sun-tap station.
Finally, after passing over a chain of darkened mountains, eerily
lighted at the pe