When they were through with the suit checkout they studied each other. Stone’s suit was gleaming white, with bright blue Mars overboots, and the Stars and Stripes proudly emblazoned on his sleeves.

Stone asked: “Are we done?”

She was sealed off from Challenger: locked inside her own, self-contained, miniature spacecraft. She took a deep breath of cool, blue oxygen. “Yes. Let’s get on with it.”

“Roger.” He looked away from her to talk to Gershon, who was up in the ascent stage. “Ralph, we’re waiting for a Go for depress on time.”

“Rager, Phil; you have a go for depress.” Gershon would monitor this first EVA from the ascent-stage cabin.

Stone closed a switch on the wall; York heard sound leak out of the air, and the internal noise of her own breathing seemed to grow louder, more ragged, to compensate.

“Roger,” Stone said. “Everything is go here. We’re just waiting for the cabin to bleed enough pressure to open the hatch.”

The gauge, York saw, showed the pressure already down to two-tenths of a pound.

Gershon said, “I’m reading a real low static pressure on your lock. Do you think you can open the hatch yet?”

Stone said, “I’ll try.”

The exit from the airlock was a small hatch, close to the floor. The handle was a simple lever. Stone bent down, twisted the handle, tugged. York could see the thin metal of the hatch bow inward. The hatch stayed shut.

“Damn it.”

“Let me try.” She crouched down and picked at the corner of the hatch, where it protruded from the wall. Her gloves, of metal mesh and rubber, were clumsy; her hands felt huge and insensitive. But she managed to get a little flap of the hatch peeled back.

Through the sliver she’d opened up between the hatch and its frame, she could see ocher light.

“I think I broke the seal.”

Stone pulled at the handle, and this time the hatch opened easily.

York saw a little flurry of snow as the last of their air escaped into the Martian atmosphere.

They both had to back away to let the hatch swing back.

Then York could see the porch, the platform fixed to the top of Challenger’s squat landing leg, onto which Stone would back out in a moment. The porch was coated in brown grit, thrown up by the landing. And beyond the porch, she could see the surface of Mars: it looked like sand, and it was streaked with radial lines pointing away from Challenger, showing the effects of their descent engine’s final blast.

It was just a scrap of landscape; on Earth it would look so commonplace she wouldn’t even perceive it. But it was Mangala Vallis: and there were only a few feet of thin Martian air separating her from the surface she’d been studying all her adult life.

“Natalie,” Stone said.