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tracked a hundred kilometers of tubing, a curiosity was discovered as
cartographers fit the positional data points onto ever-refined maps.
The tubing, which at first had appeared to run straight as an arrow, did not
follow a great circle on the globe, nor did it run truly east-west along a
latitude line around thesouth pole . Instead, curve-fitting programs confirmed
that the actual positions of the tube fit a spiral, and the center of the
spiral lay close to the pole. The whole thing looked like a giant burner on an
old-fashioned electric stove.
If the tube truly followed a spiral, it would wrap around the pole many times.
Still more precise curve-fitting procedures were performed. Projection of the
calculated spiral pattern indicated that the
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coils would be spaced roughly six hundred meters apart at this distance from
the pole.
The geophysical probes were pressed back into service, surveying six hundred
meters south of the line of the tube. A possible signal was buried in the
noise, at 623 meters. A new drill hole probing the
3.2-billion-year stratum uncovered another tube segment running east-west. Or
rather, it was not really another tube segment, but what came to be viewed as
the next coil of the same tubing as it wrapped around the pole.
What would be found at the pole itself?
Geophysical probing around the true pole found nothing. Drilling found
nothing.
Meanwhile, the cartographers refined their curves. The new solution put the
center of the spiral not at the south pole , but offset about twenty-five
kilometers from it, generally in the direction of Hellas basin.
They moved the geophysical probing efforts to that site and found evidence for
a massive metal-rich complex beneath the surface. The polar sediments were
deeper here. The complex was buried at the
3.2-billionyear stratum at a depth of thirty-two kilometers, out of reach of
any excavations.
"At that point a different kind of information came into the picture," Elena
was telling them. The bus had rolled to a stop in the valley mouth and they
were suiting up. "In the late twenties they had begun mapping a paleomagnetic
field of Mars. There's not much of a field now, of course, but three billion
years ago the magnetic dipole field was pretty healthy around here. Way above
the solar wind background. Of course, it showed a certain amount of wander.
Fluctuated in strength and went through polarity reversals. The geophysicists
developed some preliminary mapping of the pole positions as a function of
time. Guess what? Our metallic complex was buried at the position where the
magnetic pole was, 3.2 billion years ago. Near as they could tell anyway. This
whole thing was somehow designed around the magnetic field of the planet at
that time."
"Planetary engineering!"
"At least planetary-scale engineering."
"But what did it do? What was it for?"
"Nobody's got the foggiest." Lena was smiling and obviously enjoying herself
for the first time in days.
Stafford explained, "That's how we can be so firm on the date, we've got two
independent lines of evidence, like we mentioned yesterday. The pole position
and the date of the strata both say this thing was emplaced 3.2 billion years
ago. The error bars are pretty sloppy, maybe plus or minus 0.05 billion, but
it's somewhere around 3.0, 3.2, 3.3."
"One thing bothers me," Philippe said. He had a very serious expression. "If
this thing is less than a meter wide, and spaced six hundred meters apart,
weren't you incredibly lucky to hit a piece of it with a drill?
Do you expect us to believe that?"
Stafford: "We musta had two hundred drill holes out there by the time we hit
it. If you figure the tube is nearly a meter across and lines of tube are six
hundred meters apart, we were getting a fair chance of hitting it. Woulda hit
it sooner or later."
"C'mon," Elena called to them from the front of the bus. "Get your helmets on.
We're going out there."
After they were out on the surface, Carter discovered he had been so excited
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