His hands were shaking so badly all he could see at first was a blurry jumbled image. Fiercely, snarling inwardly, Jamie forced himself to a desperate calm, like a frightened man who knows he must aim his gun accurately or be killed.

The dark cleft in the rocks steadied and pulled itself into sharp focus. Deep inside it, well into the shadows of the overhang, Jamie saw the flat surfaces and crenellated outline of whitish rocks.

He was icy cold now. They’re rocks, he told himself. Not buildings. Just a formation of rocks that look roughly like walls and towers made by intelligent creatures.

And yet.

Jamie cranked the lens to its fullest magnification, then squeezed the camera’s trigger until its tiny beeping told him the cassette had been used up. Only then did he take the vidcam from his eyes.

"I’m coming up," he said, shouting even though the microphone built into his helmet was bare centimeters from his lips.

Vosnesensky sounded surprised. "Is something wrong?"

"No, Mikhail, nothing’s wrong. Something’s right."

"What? What did you say?"

It took more than fifteen minutes for the winch to lift him back to the rim of the canyon. Jamie had not realized he had traversed so far down. He spent the time trying to see more of the cleft, trying to convince himself not to let his imagination run loose, trying to stay calm and not babble once he got up there with the Russian again.

From the rim he could not see the cleft. As he shrugged himself out of the harness he said hurriedly to Vosnesensky, "Get into the rig, Mikhail. Quick! There’s something down there you’ve got to see."

"Me? Why…"

"No time for discussion," Jamie urged as he slipped the harness over the Russian’s fire-red backpack and started buckling it across his chest.

Puzzled, reluctant, Vosnesensky pulled the thigh straps tight and clicked them to the locking mechanism on his chest while Jamie reloaded the camera.

"What is it?" he asked. "What have you found?"

"A mirage, I think," Jamie said. "But maybe…"

Swiftly he described the cleft and the shapes inside it. Vosnesensky said nothing as he backed himself to the lip of the rimrock and stepped off.

"Wait!" Jamie yelled. He shoved the camera into Vosnesensky’s gloved hands and fastened its tether to his equipment belt. "Use it as a telescope. But shoot the whole damned cassette. Keep shooting until it’s all used up."

"Where do I look?" Vosnesensky asked as he descended. To Jamie he looked like an old-fashioned deep-sea diver lowering himself into the abyss.

Jamie kept rattling off instructions as the winch motor hummed thinly and Vosnesensky dropped lower.

"I see it!" For the first time since he had met the Russian, Vosnesensky sounded excited. "Yes, interesting formations of rock inside…" His voice trailed off.

"What do you think?" Jamie asked.

No answer for many minutes. Then, "It can’t be a city. It looks like rock formations."

"Yeah." Jamie paced nervously back and forth along the canyon rim. Down below the Russian was silent.

Finally, "The tape is finished. I am coming up."

"Is it real?" Jamie asked as the winch labored, whining.

"Real, yes. But not artificial. It could not be."

"Never mind what it could or couldn’t be. What is it?"

"Unusual formations of rock. But natural, not man-made."

"Martian-made."

"Not that either."

Jamie knew he should agree. It couldn’t be artificial. It couldn’t be a village created by intelligent Martians. It couldn’t be the ancestors of his ancestors, the forerunner of Mesa Verde and the other cliff dwellings of the Anasazi. He knew it could not be.

But by the time Vosnesensky was standing beside him once more and pulling free of the harness Jamie was babbling, "We’ve got to get the rover to that spot on the rim, right on top of it, so we can lower down and look in there for ourselves. We’re too far away to make certain from this distance and if there’s any chance, any slightest chance at all, that we’ve found the remains of intelligent life, holy Christ, Mikhail, it’s the biggest discovery in the history of the world!"

Vosnesensky remained strangely silent, like a stolid schoolmaster who is accustomed to sudden enthusiasms from his young students. Jamie kept on chattering and the Russian remained silent as they took the winch apart, stowed it in the rover’s equipment module, and then clumped into the airlock.

Once inside the living section they took their helmets off. Jamie could see that Vosnesensky looked solemn, almost pained. His heavy jaw was covered with several days’ stubble, making his face seem even grimmer than usual.

He realized he had been virtually raving. "Well, we can drive over there tomorrow morning, first light. Right?"

The Russian shook his head. "Not right. We have been ordered to return to the base."

"Ordered? By whom? When?"

"This afternoon, while you were down in the climbing rig. The order came over the command frequency; I heard it in my suit. Dr. Li himself specifically ordered us to return to the base camp. There has been an accident."

"It looks good enough to eat," quipped Leonid Tolbukhin. "Like a big potato."

Isoruku Konoye said nothing. The Japanese geochemist felt strangely tense as he and the cosmonaut approached the lumpy irregular blob of the Martian moon Deimos. To the Russian it might look like something to eat; to him it seemed like a huge brooding mass of darkness, evil and dangerous.

Mars has two moons, tiny chunks of rock named Phobos and Deimos, fear and dread, fitting companions for the god of war.

At first glance the moons of Mars do look rather like battered potatoes. Neither of them is round. They are too small to have been subjected to the forces that turn a lump of stone and metal into a spherical shape. Both are deeply pitted from meteorite strikes. Phobos is streaked with inexplicable striations, grooves that look almost as if its rocky surface had been scored by the claws of a titanic beast.

Deimos, the smaller of the two, is about the size of Manhattan Island: roughly ten by twelve by sixteen kilometers. It orbits just over twenty thousand kilometers above the surface of Mars. From the ground it looks like a very bright star that hangs in the sky for two and a half sols before dipping below the horizon.

Phobos is twenty by twenty-three by twenty-eight kilometers and orbits much closer to its planet, less than six thousand kilometers above the surface. It crosses the Martian sky in only four and a half hours, hurtling from west to east like an artificial satellite (which it was once suspected to be) and rising again about six and a half hours later.

It is believed that Deimos and Phobos were originally asteroids, perhaps members of the great belt of minor chunks of rock and metal that orbits between Mars and the giant planet Jupiter. Eons ago they drifted close enough to be captured by the red planet’s gravitational field and fall into satellite orbits around it.

Thus, studying Phobos and Deimos can teach us much about the farther asteroids.

Most of the meteorites that have hit the Earth were originally asteroids. The Martian moons resemble the type of meteorites called by astronomers "carbonaceous chondrites." Such meteorites have been found to contain not only carbon compounds, but water, locked in chemical combinations called "hydrates" within the meteorite’s rocky materials.

If the moons of Mars are rich in hydrates and carbon compounds, even though the water is not in liquid form, biologists will want to study the moons for signs of life or its precursors. Hydrates are immeasurably valuable to astronautical engineers, as well. They could supply life-giving water and oxygen. More important, water can be split into hydrogen and oxygen, which can be used for rocket propellants, which could cut in half the tonnages needed to be sent off Earth for any future missions to Mars.