“What?”

“Smooth. Streamlined.” Like islands, their flanks smoothed out, left stranded by the drying out of a parent river. “And I can see what look like bars of gravel, some maybe twenty, thirty feet high. Kind of like sandbanks. They seem to have formed behind outcroppings, maybe of loess, or bedrock. Like tails. The rock has grooves scoured in it. Longitudinal. The grooves flow past the islands, and the gravel bars.”

He came to a bed of loose clay and sand. “This is more loess, I think. I see—”

“What?”

“Ripples. Kind of frozen here, in the loess. Like small dunes, I guess. The dunes are stratified. It looks as if a river has dried out here.” He stalked on over the rock. “I have pits in the rock surface. Circular, a few inches deep, width from a foot wide upward. Scallop pits, I think.” Gouged out by pebbles, carried by turbulence… “The whole place is kind of like a river bottom,” he said. “Yeah. You basically have the topography of a dried-out river bottom — but magnified. Channels and bars and islands. All shaped by flowing water on a massive scale…”

He looked around with a new excitement, seeing the geology with new eyes, with Natalie York’s eyes: the deep-carved, breached channels, the huge deposits of loess, the carved-out islands. “Christ. Is that it, Natalie? Is that what you’ve brought us out here to see? Was all of this region formed by a flood?”

“You’re speculating again, Stone.”

“Oh, come on, York.”

“Okay. You’re right, Phil. At least, that’s the favored hypothesis.”

Bleeker gave up on the half-assembled CELSS, and came to stand close to Stone. “What is?”

York said, “In the Late Pleistocene — maybe twenty thousand years ago — much of Idaho and west Montana was covered by an immense lake. Called Missoula. Thousands of square miles of it. The lake was contained by an ice dam. The dam eventually burst, and released a catastrophic flood that swept over this area. Tens of millions of cubic yards per second, maybe a thousand times as much as the Amazon’s discharge rate—”

“Jesus,” Stone said.

“Yeah. The existing streamways couldn’t cope with the sudden volume, so they burst; the valleys were widened and deepened, and interconnecting channels were cut — all the way into the bedrock — in hundreds of places. Thousands of square miles were swept clean of the superficial structures, right down to the basalt bedrock, and another thousand square miles were buried in river-bottom debris.

“We’re left with hundreds of cataract ledges, basins, and canyons eroded into the bedrock, isolated buttes and uplands, gravel bars thirty or forty yards high.

“This is the scabland, Phil. There are only a handful of areas on Earth which show the effects of large-scale, catastrophic flooding so well.”

Bleeker pushed back his Snoopy hat and scratched his blond head. “It’s fascinating, Natalie. But I don’t see what it has to do with us.”

“Okay. Phil, I’ve given you another pack of photographs. In the left side-pocket of Adam’s pack.”

Stone dug into Bleeker’s pocket and pulled out a plastic packet of black-and-white photographs. He leafed through them quickly, showing them to Bleeker.

Cratered plains: the images were of Mars, clearly enough. But there was a channel cut deeply into what looked like the tough, ancient landscape of the southern hemisphere. There was a crater complex, overlaid by anastomosed channels. There was a crater with a teardrop-shaped, streamlined island, like a gravel bar, collected in its wake; and “downstream” of the crater, there were scour marks, running parallel to the island…

Stone was having trouble making sense of what he saw and heard. “Are you saying that Mars has suffered catastrophic flooding — like the scabland here, in Washington State?”

York hesitated. “I believe so. A lot of us have argued that, since the Mariner pictures came in. I’ve been studying the area you’re looking at, in those photos, since 1973. I guess I’m the leading expert on it, now. And it seems to me the analogy between the terrestrial scabland features and the Martian morphology is too striking to be a coincidence.”

“But not everybody agrees,” Stone hazarded.

“No,” she conceded. “Some say the Martian ‘scabland’ features are too big to have been formed by water. Schumm, for instance.”

“Who?” Bleeker asked.

“Schumm says the Martian channels must have been formed by tensional factors in the planet’s surface. Cracks, modified later, maybe, by vulcanism and the action of the wind.”

“Sounds like an asshole to me,” Stone said, peering at the pictures. “I’m with you, Natalie.”

“But if these Martian channels were formed by flooding,” Bleeker said, “where the hell did the water come from? And where did it go?”

“I’ll bet she has a theory about that, too,” Stone muttered.

“I didn’t copy, EV1.”

“Go ahead, Natalie.”

“Underground aquifers. Contained by tough bedrock below — maybe ten miles deep — and a cap of thick ice in the regolith above. Whatever lifted up Tharsis — a convection process in the mantle, maybe — must have caused the faulting that led to the flooding. The pressure of the water has to exceed the pressure of the rocks. All you’d need would be a breach on the subsurface ice cap for the water to gush to the surface, under high pressure.”

“My God,” Stone said. “Oceans, buried in the Martian rocks. How can we find out if you’re right, Natalie?”

“What we need is for three guys to land there in a MEM, and dig a few deep cores.”

Stone started to see where all this was leading. He leafed through the photos again. “What area are these photos of?”

“That’s one of the most striking outflow channels. It’s Mangala Vallis, Phil. Martian scabland: your landing area.”

Stone grinned. She’s doing it again. Mangala Vallis. On which Natalie York, leading light of the site selection committee and would-be Mars voyager, just happens to be the world’s top expert.

And Adam Bleeker still doesn’t know what anastomosis is. I hope the guy’s watching his back. Mission Elapsed Time [Day/Hr:Min:Sec] Plus 349/11:14:03

Two months out, Mars had been the brightest object in the sky save the sun, but still a starlike point. Then — twenty days from orbit insertion — Mars had opened out into a disk. And where the line between light and dark crossed the planet, she could see, with her naked eye, wrinkles and bumps: craters and canyons, catching the light of the sun.

Gradually, as the days had unfolded, she’d made out more and more recognizable detail on the surface. There was the huge gouge of the Valles Marineris — a wound visible even from a million miles out — and the polar cap in the north, swelling with water ice in advance of the coming winter, and the great black calderas of the Tharsis volcanoes.

It was remarkable how much she could recognize. Almost as if she had been here before.

Mars was clearly a small world, she thought. Some of the features — Tharsis, the Marineris canyons, Syrtis, the great iced pit of Hellas in the south — sprawled around the globe, outsized, dominating the curvature.

In some ways Mars was as she had expected. It looked a lot like the big photomosaic globes at JPL. But there were surprising differences, too. Mars wasn’t red so much as predominantly brown, a surface wrought out of subtle shadings of tan and ocher and rust. There was a sharp visible difference between northern and southern hemispheres, with the younger lands to the north of the equatorial line being brighter in color, almost yellow.

Ares was approaching the planet at an angle to the sunlight, so Mars was gibbous, with a fat slice of the night hemisphere turned toward the spacecraft. And the ocher shading seemed to deepen at the planet’s limb, and at low sun angles. These features gave the little globe a three-dimensional effect, a marked roundness. Mars was a little round orange, the only object apart from the sun in all the 360-degree sky visible as other than a point of light.