showing a sectional view through the Lunar center. “You can see it
on this. The red shell is the original outer crust going right
around-it’s roughly circular, as you’d expect. On Farside-
here-this blue stuff sits on top of it and wasn’t added very long
ago.”
“On top of what used to be the surface.”
“Exactly. Somebody dumped a couple of billion tons of junk down on
the old crust-but only on this side.”
“And that’s been verified pretty conclusively?” Hunt asked, just to
be doubly sure.
“Yeah. . . yeah. Enough bore holes and shafts have been sunk all
over Farside to tell us pretty closely where the old surface was.
I’ll show you something over here . . .” A major section of the far
wall comprised nothing but rows of small metal drawers, each with
its own neatly lettered label, extending from floor to ceiling.
Steinfield walked across the room, and stooped to scan the labels,
at the same time mumbling to himself semi-intelligibly. With a
sudden “That’s it!” he pounced on one of the drawers, opened it,
and returned bearing a closed glass container about the size of a
small pickle jar. It contained a coarse piece of a light gray rocky
substance that glittered faintly in places, mounted on a wire
support.
“This is a fairly common KREEP basalt from Farside. It-”
“‘Creep’?”
“Rich in potassium-that is, K-rare earth elements, and phosphorus:
KREEP.”
“Oh-I see.”
“Compounds like this,” Steinfield continued, “make up a lot of the
highlands. This one solidified around 4.1 billion years ago. Now,
by analyzing the isotope products produced by cosmic-ray exposure,
we can tell how long it’s been lying on the surface.
Again, the figure for this one comes out at about 4,100 million
years.”
Hunt looked slightly puzzled. “But that’s normal. It’s what you’d
expect, isn’t it?”
“If it had been lying on the surface, yes. But this came from the
bottom of a shaft over seven hundred feet deep! In other words, it
was on the surface for all that time-then suddenly it’s seven
hundred feet down.” Steinfleld gestured toward the wall chart
again. “As I said, we find the same thing all over Farside. We can
estimate how far down the old surface used to be. Below it we find
old rocks and structures that go way back, just like on Nearside;
above it everything’s a mess-the rock all got pounded up and lots
of melting took place when the garbage came down, all the way up to
what’s now the surface. It’s what you’d expect.”
Hunt nodded his agreement. The energy released by that amount of
mass being stopped dead in its tracks would have been phenomenal.
“And nobody knows where it came from?” he asked.
Steinfield repeated his head-shaking act. “Some people say that a
big meteorite shower must have got in the way of the Moon. That may
be true-it’s never been argued conclusively one way or the other.
The composition of the garbage isn’t really like a lot of
meteorites, though-it’s closer to the Moon itself. It’s as if they
were made out of the same stuff-that’s why it looks the same from
higher up. You have to look at the microstructure to see the things
I’ve been talking about.”
Hunt examined the specimen curiously for a while in silence. At
length he laid it carefully on the top of one of the benches.
Steinfield picked it up and returned it to its drawer.
“Okay,” Hunt said as Steinfield rejoined him. “Now, what about the
Farside surface?”
“Kronski and company.”
“Yes-as we discussed yesterday.”
“The Farside surface craters were made by the tail end of the
garbage-dumping process, unlike the Nearside craters, which came
from meteorite impacts oh. . . a few billion years back. In rock
samples from around the rims of Farside craters we find that things
like the activity levels of long half-life elements are very
low-for instance, aluminum twenty-six and chlorine thirty-six; also
the rates of absorption of hydrogen, helium, and inert gases
from the Solar wind. Things like that tell us that those rocks
haven’t been lying there very long; and since they got where they
were by being thrown out of the craters, the craters haven’t been