h, starchy liquid that they could
suck through a tube from the air-restorers--it was a by-product of the
photosynthetic process--might even have sustained them for a
considerable interval.

But the steady weakening of their nuclear batteries was another matter.
The pumps of their air-restorers and moisture-reclaimers were dependent
on current. Gradually the atmosphere they breathed was getting worse.
But from reports they had read and TV programs they had seen long ago,
they found themselves another faint hope, and worked on it. With only
solar power--derived through worn-out thermocouple units--to feed their
uncertain ionics, they could change course only very slowly, now.

Yet maybe they had used up their bad luck. At last they came to a
surface-fragment a couple of hundred yards long. They climbed over its
edge. The thin sunshine hit dried soil, and something like corn-stubble
in rows. Ahead was a solid stone structure, half flattened. Beside it a
fallen trunk showed its roots. Vegetation was charred black by the
absolute dryness of space. There was a fragment of a road, a wall, a
hillside.

Here, there must have been blue sky, thin, frosty wind. The small,
Mars-sized planet had been far from the sun. Yet perhaps the greenhouse
effect of a high percentage of carbon dioxide in its atmosphere and the
radioactive heat of its interior had helped warm it. At least it had
been warm enough to evolve life of the highest order, eons ago.

Poof had gone the blue sky and this whole world, all in a moment, the
scattered pieces forming the asteroids. Accident? More likely it was a
huge, interplanetary missile from competing Mars. The Martians had died,
too--as surely, though less spectacularly. Radioactive poison,
perhaps... Here, there had been an instant of unimaginable concussion,
and of swift-passing flame. The drying out was soon ended. Then, what
was left had been preserved in a vacuum through sixty millions of years.

Frank Nelsen had glimpsed ancient Mars, preserved on the Moon. Now he
glimpsed its opponent culture, about which more was generally known.

"It's real," Ramos grunted. "Hoppers find surface-fragments like this,
quite often."

Nelsen hardly cared about the archeological aspects just then.
Excitement and hope that became certainty, enlivened his dulled brain.

"An energy source," he grated joyfully. "The Big Answer to Everything,
out here! And it's always self-contained in their buildings..."

They pu