It was cold. The shock of it hit Nadia in the forehead, and the eyes. It was hard not to gasp a little. Going from 500 millibars to 340 would no doubt account for that. Her eyes were running, her nose as well. She breathed out, breathed in. Her lungs ached with the cold. Her eyes were right out in the wind— that was the sensation that most struck her, the exposure of her eyes. She shivered as the cold penetrated her walker’s fabrics, and the inside of her chest. The chill had a Siberian edge to it, she thought. 260Âdeg;K,—13° Centigrade— not that bad, really. She just wasn’t used to it. Her hands and feet had gotten chilled many a time on Mars, but it had been years and years— over a century in fact!— since her head and lungs had felt the cold like this.

The others were talking loudly to each other, their voices sounding funny in the open air. No helmet intercoms! Her walker’s neckring, where the helmet ought to have rested, was extremely cold on her collarbones and the back of her neck. The ancient broken black rock of the Great Escarpment was covered with a thin night frost. She had peripheral vision such as she never had in a helmet— wind— tears running down her cheeks from the cold. She felt no particular emotion. She was surprised by how things looked unobstructed by a faceplate or any other window; they had a sharp-edged hallucinatory clarity, even in starlight. The sky in the east was a rich predawn Prussian blue, with high cirrus clouds already catching the light, like pink mares’ tails. The ragged corrugations of the Great Escarpment were gray-on-black in the starlight, lined with black shadows. The wind in her eyes!

People were talking without intercoms, their voices thin and disembodied, their mouths hidden by the masks. There was no mechanical hum, buzz, hiss, or whoosh; after over a century of such noise, the windy silence of the outdoors was strange, a kind of aural hollowness. Nazik looked like she was wearing a Bedouin veil.

“It’s cold,” she said to Nadia. “My ears are burning. I can feel the wind on my eyes. On my face.”

“How long will the filters last?” Nadia said to Sax, speaking loudly to be sure she was heard.

“A hundred hours.”

“Too bad people have to breath out through them.” That would add a lot more CO2 to the filter.

“Yes. But I couldn’t see a simple way around it.”

They were standing on the surface of Mars, bareheaded. Breathing the air with the aid of nothing more than a filter mask. The air was thin, Nadia judged, but she did not feel lightheaded. The high percentage of oxygen was making up for the low atmospheric pressure. It was the partial pressure of oxygen that counted, and so with the percentage of oxygen in the atmosphere so high. . . .