What did you expect? he asked himself. Something as obvious as the San Andreas Fault?

"Time to come up," Vosnesensky called. "Now."

Despite himself Jamie leaned back in the harness and looked up. For a dizzying moment he felt as if the rock wall were tipping over to fall in on him.

But he heard himself complain, "I haven’t reached the bottom yet!"

"It is getting dark."

Swaying in the harness, Jamie realized that the shadows from the opposite canyon wall were almost upon him. He shuddered. Mikhail’s right; I don’t want to be down here in the dark.

"Okay, coming up," he said into his helmet microphone. He felt the harness tighten about him as the cable began pulling him. He held onto the cable with both gloved hands and tried to gain some purchase on the rock face with his boots as he rose. The winch did all the real work.

At last he reached the top. The sun was almost on the horizon. Even inside the heated suit Jamie shivered. The sky to the east was already dark.

Vosnesensky helped him remove the harness and equipment belt; then they started back toward the rover.

Jamie halted his companion with an outstretched hand.

"Wait a minute, Mikhail. We’ve been on Mars almost a week and we haven’t really watched a sunset."

The Russian made a sound halfway between a grunt and a snort, but he stopped. The two of them stood there on the broad Martian plain, their hands filled with the climbing equipment, and watched the tiny pale sun touch the flat horizon. The sunset was not spectacular. No flaming colors of breathtaking beauty. The air was too thin, too dry, too clean. And yet…

The pink sky deepened into red, then violet, uniformly, evenly, the way the dome of a planetarium softly dims when its lights are turned down toward darkness.

"Look!" Jamie pointed as the sun dipped out of sight. A single lonely wisp of a cloud hung above the horizon, glowing like a silver ghost briefly. Then the sun disappeared and the cloud faded into the all-encompassing darkness.

"This is more beautiful than I could have imagined." Vosnesensky’s voice was softer, gentler than Jamie had heard before.

"It sure is. I wonder…"

Jamie’s words died in his throat. His heart began to pound. The sky was shimmering, glowing faintly as a spirit hovering above them, flickering colors so pale and delicate that for a breathless moment Jamie could not believe his eyes.

"Mikhail…"

"I see it. Aurora."

"Like the northern lights." Jamie’s voice was hollow with awe, trembling. The lights pulsed and billowed across the sky, exquisitely ethereal pastels of pink, green, blue, and white. He could see stars through them, faintly.

"But Mars has no magnetic field," Vosnesensky said, sounding more puzzled than impressed.

"That’s just it," Jamie heard himself reply. "Particles from the solar wind must hit the upper atmosphere all across the planet. The gases up there glow when the particles excite them. This must be going on everywhere, every night. We’ve just never stayed out long enough to see it."

"Wouldn’t it be observable from orbit?" Mikhail was being more of a hardheaded scientist than Jamie.

"Must be pretty faint, looking down against the background of the planet itself. But if they know what to look for I’m sure Katrin Diels and Ulanov will be able to observe it."

The colors faded away. The lights died slowly, leaving the sky calm and dark. Jamie felt a shudder race through him, though whether it was fear or ecstasy he could not tell. Probably some of both. His pulse was still thundering in his ears. As far as the eye could see in any direction, there was nothing but utter darkness now. As if the world had vanished, as if he were standing alone in a universe all his own, unpopulated, unoccupied except for himself.

And the stars. Even through the tinted visor of his helmet Jamie saw the bright eternal stars looking down at him like faithful old friends, telling him that even on this strange empty world they were up there in their places, the guardians of universal order.

One of the stars was visibly moving across the sky. "Is that our ships in orbit?" Jamie wondered aloud.

Vosnesensky chuckled. "It is Phobos, so close it looks like a space station, going from west to east. Deimos is too faint to see unless you know exactly where to look for it."

Jamie recognized Orion and Taurus, with the cluster of the Pleiades in the bull’s neck. Turning, he saw both the Dippers. The North Star isn’t over the north pole of Mars, he remembered.

"Look there." Vosnesensky must have been pointing, but with nothing except starlight Jamie could not make out his form.

The Russian took him by the shoulder and turned him slightly. "Just above the horizon. The bright blue one."

Jamie saw it. An incredibly beautiful blue star shimmering low on the horizon.

"Is it Earth?" he asked, in a reverent whisper.

"Earth," replied Vosnesensky. "And the moon."

Jamie could not make out the fainter whitish star nearly touching the blue one. Vosnesensky insisted he could, but Jamie thought it might have been more the Russian’s imagination than superior eyesight.

"We must get back inside the rover," Vosnesensky said at last. "No sense freezing to death while admiring the sky."

He turned on his helmet lamp, immediately destroying their night-adapted vision, and then touched the controls on his wrist to remotely turn on the lights in the rover. Reluctantly, almost angry at the cosmonaut, Jamie followed Vosnesensky back to the vehicle.

It took a surprisingly long time to get out of their hard suits in the confined space inside the rover’s airlock. The excitement of discovering the aurora gradually dimmed away. By the time they were down to their tubed skivvies, sitting on folded-up bunks facing each other with a pair of microwaved meals on the narrow table between them, Jamie’s pulse had returned almost too normal.

Vosnesensky hoisted his water glass. "A very good day," he said. "We accomplished much."

Jamie touched his plastic glass to the Russian’s. "You’ll have a good report to make to Dr. Li."

"Yes, after we eat."

"I’ll feed the data tapes into the computer."

"Good. Then we call the base and see what they have been doing."

Jamie leaned forward over the narrow table. "Mikhail, I have a suggestion about tomorrow."

The Russian also hunched slightly forward, until their noses were almost touching.

"No more than a day or so to the east of here, if we drive steadily, is Tithonium Chasma, part of the Valles Marineris complex — much deeper and wider than…"

Vosnesensky was already shaking his head. "It is not on the excursion plan. It is too far for us to travel."

"It’s less than six hundred kilometers from here," Jamie argued. "We could do it in twenty hours if we didn’t stop."

"Drive at night? Are you insane?" There was no fear in the cosmonaut’s sky-blue eyes, merely the unshakable firmness of a man who had already decided how many risks he was prepared to take.

Jamie said, "Let me explain the geological necessity."

Strangely the Russian broke into a lopsided grin. "Fine. You explain geology. I will clear the table."

As Vosnesensky got up and took their dinner trays to the storage rack where they would remain until the rover returned to the main base, Jamie folded the table and slid it back into its place beneath the bunk.

"The canyon walls here are undifferentiated," Jamie began to explain. "Just one big slab of iron-rich rock that’s been worn away and exposed. That’s unheard-of, Mikhail. There’s nothing on Earth like that."

"So you have made a great discovery. Good."

"We’ve got to find out if the bigger canyons are like that! Is the whole canyon system that way? Three thousand kilometers of pure mantle rock? It can’t be! It just can’t be."