The next thing he felt was a slight bouncing jolt-as if he were aboard an old-fashioned elevator which had reached its floor. He half expected a chime to sound and the doors to open. Instead, the pod erupted with the cheers of the cadets who threw off their webbing straps and jumped to their feet to clap one another on the back in the jubilation of all travelers who arrive safely at their destination.

From the racks behind each seat they took down the elasticized surface suits and began wriggling into them. The suits designed for Mars were simple, tight-fitting polymerized one – piece elastic suits much like ocean divers wore. All the necessary pressure was supplied by the girdling effect of the elastic. A mushroom-shaped helmet attached to a wide neck seal on the suit completed the ensemble. The helmet had a hemispherical visor which allowed full vision in every direction. At the back of the helmet, a built-in canister held oxygen pellets for extended rambling on the surface of the planet.

When all helmets were in place, the hatch was popped and each explorer filed past Packer who stood at the portal and affixed his yellow triangular stickers to each helmet as he checked each suit. Spence stood last in line behind Adjani and, after the once over by Packer, stepped out into the rust-colored world.

He bobbed down the steps of the hatch and walked a few paces in the red dirt that powdered beneath his feet. His motions were exaggerated and springy-an effect of the reduced gravity of Mars. He grinned from ear to ear with the exhilaration of just being there, a human being treading on alien soil. He felt strong, invincible-also an effect of reduced gravity.

He scanned the horizon of the planet and was surprised to find how close it was and how sharp the curve. He turned to scan the points of the compass. Everywhere he turned the same dull red, brick-colored dirt met his gaze, as if he were lost in a mono chromatic desert. Rocks of various sizes poked through the red soil; some of these were a shade or two lighter or darker than the dirt around them, providing the only contrast he could see.

At the horizon the sky burned a brilliant blue, as if infused with fire. The blue gradually darkened to jet black directly overhead. Spence soon found that this changed dramatically depending upon the time of day. At high noon the sky was pink. At sunset it glowed with golden warmth at the horizon while stars shone hard and bright above like gems spilled out upon a cloth of blackest velvet.

Low in the sky one of Mars' tiny twin moons hovered above the faraway mountain range. At least Spence took it to be faraway. Without a heavy atmosphere to distort images and clothe them in misty shrouds, objects and landforms on Mars appeared hard-edged and distinct whether close at hand or faraway.

Across a stretch of the arid soil he viewed a loose assemblage of buildings huddled, dome-shaped like a cluster of toadstools – the terraforming installation, one of five on the planet-but whether it stood two kilometers or ten distant, he could not tell.

He heard a buzzing in the air and turned to find its source. He was surprised to see Packer standing atop the hatchway with his helmet in his hands shouting at them as his face grew bright red.

"Take off your helmets!" he called. Through the helmet's insulation the words sounded as if he were shouting at them from one end of a very long hose.

Tentatively Spence grasped the sides of his helmet and gave it a sideways twist. He heard the pressure hiss away and felt his ears pop as if he had suddenly leaped to a high altitude.

He took a breath and found that he could not stop inhaling.

"It's all right," Packer said a little breathlessly. "Just breathe easy. Don't overdo it. Relax and let your body adjust to it."

There were oohs and ahhs all around as the cadets experienced this wonder of breathing the thin Martian air.

"I wanted you to see that you can breathe without a helmet if necessary. The atmosphere is still mostly carbon dioxide – that's why your lungs feel as if they can't get enough. But we have been able to enrich the atmosphere by a few percentage points. There is enough oxygen to support life for short periods of time if you do not tax it. You could not run or even walk quickly before you passed out. But you will not die of suffocation, either, if you don't exert yourself.

"Your more immediate danger is the temperature. I'm sure you are all aware that during the day the temperature this time of year is a uniform 25 degrees celsius. As the sun goes down the temperature plunges to minus 105. Your suits offer some protection from the violent swing in temperature, but they are not designed to be used during the chill of a Martian night."

Packer raised his helmet over his head. "All right, put your helmets back on and let's track it to the installation." He pointed toward the cluster of buildings.

Spence raised his helmet and paused to breathe once more the incredibly dry, thin air, tasting its metallic tang on his tongue. He closed his eyes and drew it deep into this lungs where it burned with tingling fire. It seemed almost as if he were standing on a mountaintop – the effect was the same.

"Remarkably like the Himalayas," said a voice beside him.

He opened his eyes and grinned at Adjani standing at his elbow. "I was thinking of the Rockies, myself. I've never been to the Himalayas."

They replaced their helmets and Spence tasted the sweet oxygen as he breathed it in. He adjusted the voice amplifier so that he could speak to Adjani-Adjani did the same-and they trudged off behind the bouncing column of cadets with Packer in the lead.

The terraforming project was in its fifth year on Mars. At the present stage it took the form of enormous greenhouses filled with broad-leaf plants genetically engineered to be virtual oxygen factories. The greenhouses pumped in the carbon dioxide of Mars and flushed out the oxygen waste of the plants. Beneath the greenhouses, nuclear reactors maintained optimum temperatures, heating the plants through long, impossibly cold nights.

The greenhouses were established and working according to plan. This trip inaugurated phase two of the project: melting the enormous polar ice cap of the planet.

There was water on Mars; the first Voyager probes had discovered that. But it was mostly locked up with the carbon-dioxide ice at the poles. Although some minute part existed as water vapor, it was not enough to sustain plant life. By melting the polar ice, it was hoped that enough water vapor might be released to allow the planet to begin rebuilding an earth-type atmosphere. As the amount of oxygen and water vapor in the atmosphere grew, the temperature would stabilize and the mineral-rich soil though dry as desert sand-would perhaps support some varieties of plant life, and later animals and eventually man.

Terraforming was a bold idea that seemed bound to work, given enough time. Packer planned an expedition to the poles to view various sites where nuclear devices might be planted to melt the dry ice. He was anxious that terraforming of Mars be complete within his lifetime. "I want to see my grandchildren romping over the lush, green landscape of Mars," he told his cadets. He was far more taken with this project than with the plasma drive. Still, the first colonies were decades away.

Little red clouds of dust rose from the tramping feet of the cadets as they moved along the trail. By the time they reached the installation, an octopus arrangement of buildings with the central barracks surrounded by the long rows of greenhouses radiating out from the center like arms, everyone was covered with the fine rusty grit. They moved along the translucent shells of the greenhouses and Spence could see flashes of green from within, completely out of keeping with the dullness of their surroundings.