"How do I tell it to find you, Jory? I don't even have a map!"
"It's all set. I've given your proxy a homing point. See you in about ten minutes. Enjoy the ride."
"But what about—?"
From the sudden curious deadness in her earphones, she knew he had gone offline, back to whatever task he had been doing. Demeter wanted to know what would happen if she stalled the machine, or walked it off a cliff, or something.
A few minutes later, she got a short demonstration. The machine approached the top of a steep slope. The angle would be enough to put the proxy's center of gravity ahead of and outside the circle of balance defined by its leg radius. If it tried walking down, either forward or backward, or sideways for that matter, it would tumble head over—over whatever bulbous body part was following its sensory apparatus.
Instead of proceeding, the proxy stiffened in place. Demeter glanced down to see the legs folding into a springy, six-sided cage of bowed steel. With one limb, the machine pushed off, going over the edge.
Demeter's viewpoint spun end-for-end and side-for-side. Her breakfast made a quick surge in her throat and then settled down. The proxy glanced off a boulder and was briefly airborne, bouncing farther down the slope. The background sound in her ears was like a shopping cart rolling over rocks. The rollover slowed finally and stopped most of the way to upside down.
With methodical slowness, the legs unfolded and righted the body, taking Demeter's perceptions along with it. The machine seemed to shake itself, the arms came away from their reflexive clutch against the belly, and the proxy continued on its way.
After another few minutes of fast walking, it brought her to a shallow valley among the ridges somewhere east of the tunnel complex.
Demeter drew in her breath.
The valley was crawling with horseshoe crabs. Dark, humped-over bodies—that blind forward curve, the articulated back section, the wicked spike of a tail— stumbled over the nearby hills and clawed their way into a pulsing pile. Demeter was reminded of an arachnid mating ritual. A gang-bang out of the Paleozoic Era. Trilobite City!
Demeter had heard that Mars had some native life-forms, mostly one-celled colonies under mushroom caps of silicate. And there were reports of certain hardy Earth forms that had gone feral—one was a kind of gerbil that had been bioengineered for minimal respiration and cold-adaptation, locally known as the "pack rat." But she never expected these living marine fossils to come crawling out of the desert landscape.
"What are those things?" she asked. Demeter had spotted the Creole standing at the edge of the slowly pulsating pile. He was actually doing something to one of the little horrors, taking its eggs or something. With Jory for scale, she guessed each crab's carapace was about a meter across.
"Johnnies," he replied, turning around to spot her proxy. "That's what we call them, anyway. 'Von Neumann processor' is the formal name."
"It's an animal?" she asked.
"Of course not. Its just a machine, but a pretty clever one."
He explained their function, which was part exploration, part minerals processing. Powered by photovoltaic circuits imprinted in the pat tern of its shell, the mechanical trilobite crept along. Aside from chip-coordinated navigation and recording gear, and a roving command structure similar to that animating her proxy, the von Neumann consisted mostly of mouth and guts.
The mouth was a chemical analysis unit—based on the same kind of nanotech gas chromatography circuits that Dr. Lee had shot into her bloodstream—attached to a grinder and shovel. The guts were a series of tiny separators and smelters. As the machine walked over the Martian surface, its mouth sampled the soil and any likely outcroppings of rock that the cluster eyes noticed. When the parameters matched variables inscribed on its microprocessor brain, the von Neumann sat down and began to feed.
The first crop of alloys, silicates, and organic strings was passed to a third system inside the shell. This was the hatchery, where two—count 'em, two—new and full-sized von Neumanns were cast in pieces. The parent extruded them under a leveraged lift with its tail and then assembled them with a pair of micromanipulators folded under the front edge of its shell.
Once these replicas were launched and walked away to a life of wandering, sampling, recording, and eating, the mother machine settled down to really stuffing itself. Its taste and diet shifted to pure metals and crystals, stored in the half-domes under the carapace and eventually loaded into spaces formerly occupied by the replication equipment, which was similarly digested.
As soon as every spare cubic centimeter under the shell was packed with refined mineral products, the machine turned around and homed on a designated spot—this valley was one of them. "Send out one von Neumann, and eventually it comes back," Jory finished his lecture. "Then two more. Then four. Then eight. And so on, practically forever."
He picked up one of the machines, broke its back open with a wrench-thing in his hands, and extracted two copper-colored disks, a sausage that looked to be made of pure glass, and several loops of spaghetti-like fiber. These he put in bags hung around his utility harness.
"Each one is bursting with usable stuff," he explained. "Not to mention the shell itself , which is mostly soft iron with some strengthening fibers."
"Why put a shell on them at all?" Demeter asked, curious.
"Sandstorms. We get some really fast winds here, without any heat sinks like Earth's oceans, to modify the thermal absorption. The poles regulate the temperature, mostly, and they're a long way away."
"The shell keeps out blowing sand?"
"Well, no. It keeps the beast upright and moving. Aerodynamics, really." Jory spoke offhandedly, while his fingers dug and probed. "The harder the wind blows, the more stable the von Neumann becomes. Wind actually helps it dig into the ground. Otherwise it would blow around and lose its sense of direction. Then these things might never come back for collection."
"What about the proxies?" Demeter described the way her apparatus had balled up and rolled down that rocky slope. "These things stay outside all the time, right? So how come they don't blow around like tumbleweeds and get lost in the process?"
Jory shrugged. "They're smarter than a von Neumann, even without a human driver. They know how to report into the grid, which tracks them with RF beacons—most of the time. But, hell, losing the proxies occasionally is the only excitement we get around here. You'd be surprised the new territory you find that way."
Demeter seemed to remember the grids being a little less cavalier about the prospect of abandoned equipment. But the thought passed.
Jory examined the most recently gutted machine's curved shell for, apparently, breaks and scrapes. He worked its legs back and forth, and noted a broken tip on one claw. Finally, he fingered a notch in the spiked tail. With a shake of his head, Jory dismembered the von Neumann into other collection bags about his person. Then his fingers popped a tinv slab out of the last piece of shell he was holding. This item he dropped carefully into a pocket of his shorts.
"What's that?'
"Its brain. Carries an imprint of where the von Neumann went and what it saw. We'll feed that into the grid, and some cyber somewhere will add its data to our topographic mapping program. Little by little we're coming up with a really detailed survey of Mars."
After watching him tear apart three of the critters, Demeter finally asked, "Can I help?"
"Sure! It's easy!"
He showed her how to snap open the carapace, which parts were product and which process, and how to spot a damaged machine. Her manipulators worked just like normal hands, although she needed some getting used to their odd spatial orientation and the nonhuman range from eye to fingertip. Jory gave her a set of the shell-cracking tools and the sorting bags, which he hung from the knee-joints of her proxy within easy reach of her hands.