Sherrard shakes his head. Carefully he gathers one of the creatures into his gloved hands and brings it close to his faceplate. “It doesn’t move at all,” he says quietly. “It’s playing possum, isn’t it?”
“It may not be able to move,” says Leonides. “Not with anything as warm as you so close to it. They’re tremendously sensitive to heat, I imagine. You see how they start to shut down, the moment the sun strikes them?”
“Like machines,” says Sherrard. “At the wrong operating temperature they cease to function.”
“Like machines, yes,” Leonides replies. “But surely you aren’t going to try to argue that they are machines, are you?”
Sherrard shrugs. “Machines can have legs. Machines can have shells.” He looks toward me. “It’s like you said, Tom: robots left behind by explorers from some other part of the galaxy. Why not? Why the hell not?”
There is nothing to gain by debating it out here. We return to the ship to get collection chambers and scoop three of the creatures into cryotanks, along with liquid methane and lumps of frozen-ammonia ice. The discovery is so wholly unexpected and so numbing in its implications that we can hardly speak. We had thought we were making a routine reconnaissance of an unimportant planet; instead we have made one of the most astonishing discoveries in the history of science.
We store our finds in the ship’s lab at a temperature of two or three degrees Kelvin. Gartenmeister and Sherrard set about the job of examining them while Leonides and I continue the extravehicular exploration.
The crab-creatures are littered all over the place, dozens of them, hundreds, scattered like jetsam on a beach. They appear to be dead, but very likely Leonides’ notion that they are extremely heat-sensitive tells the real story: to the native life-forms of Pluto—and how strange it is to have a phrase like that running through my mind!—the coming of day must be an inexorable signal bringing a halt to all metabolic activity. A rise of just a few degrees and they are compelled to stop in their tracks, seemingly lifeless, in fact held in suspended animation, until the slow rotation of the planet brings them back, in another 6.39 Earth-days, into the frigid darkness that they must have in order to function. Creatures of the night: creatures of the inconceivable realm at the borderland of absolute zero. But why? It makes so little sense: to move by night, to go dormant at the first touch of the life-giving sun! Why? Why?
Leonides and I explore for hours. There is so much to do: collecting mineral samples, drilling for ice-cores that may yield data on earlier epochs of Pluto’s history, searching for other forms of life. We move carefully, for we are not yet used to the lightness of the gravitational field, and we prowl in a slow, systematic way, as if we are going to be the only expedition ever to land on this remote outpost of the Solar System and must take pains not to overlook anything. But I see the fallacy in that. It is true that this is the first time anyone has bothered to visit Pluto, although centuries have passed since the earliest human voyages into space. And it is true also that when we planned this expedition it was under the assumption that no one was likely to have reason to come this way again for a long time. But all that has changed. There is extraterrestrial life on this world, after all. Nowhere else is that the case. When we send back the news, it will alter the direction of virtually all scientific research, and much else besides.
The impact of our find is only just beginning to sink in.
Sherrard peers out of the ship’s lab as Leonides and I come back on board. His expression is a peculiar one, a mixture of astonishment and—what?—self-satisfaction?
“We’ve discovered how they work,” he announces. “They operate by superconductivity.”
Of course. Superconductivity occurs only within a few degrees of absolute zero: a strange and miraculous thing, that resistance-free flow of current, the most efficient possible way of transmitting an electrical signal. Why not have it serve as the energizing principle for life-forms on a world where nighttime temperatures drop to two degrees Kelvin? It seems so obvious, now that Sherrard has said it. But at the same time it is such an unlikely thing, such an alien way for living creatures to be designed. If, that is, they are living creatures at all, and not merely some sort of cunning mechanisms. I feel the hair lifting along the back of my neck.
Gartenmeister and Sherrard have dissected one. It lies on its back, its undershell neatly cut away and its internal organs exposed to view. Its interior is lined with a series of narrow glossy green and blue tubes that cross and meet at rigid angles, with small yellow hexagonal bodies spaced at regular intervals down the center. The overall pattern is intricate, yes, but it is the intricacy of a well-designed machine. There is an almost oppressive symmetry about the arrangement. A second creature, still intact, rests unmoving and seemingly lifeless in its holding tank. The third has been placed in an adjoining tank, and it is awake and sullenly scrabbling about like a trapped turtle trying to climb the walls of its bowl.
Jerking his thumb at the one that is moving, Gartenmeister says, “We’ve got it at Pluto-night temperature, just a notch above absolute. The other tank’s five degrees warmer. The threshold is very precise: when the temperature rises to seven degrees above absolute zero they start to go dormant. Lower the temperature and they wake up. Raise it again, they stop in their tracks again. It’s like throwing a switch.”
“It’s exactly like throwing a switch,” says Sherrard. “They’re machines. Very neatly calibrated.” He turns on a projector. Glittering cubical forms appear on the screen. “Here: look at the crystalline structure of one of these tubes. Silicon and cobalt, arranged in a perfect matrix. You want to tell me this is organic life? These things are nothing more than signal-processing devices designed to operate at super-cold temperatures.”
“And we?” Leonides asks. “Are we not merely signal-processing devices also, designed to operate in somewhat warmer weather?”
“Merely? Merely?”
“We are machines of flesh and blood,” says Leonides. “These are machines of another kind.”
“But they have blood also,” Gartenmeister says. “Of the sort that a superconductive life-form would have to have. Their blood is helium II.”
How startling that is—and yet how plausible! Helium II, that weird friction-free fluid that exists only at the lowest of temperatures—capable of creeping up the side of a glass vessel in defiance of gravity, of passing through openings of incredibly small size, of doing all manner of unlikely things—and of creating an environment in which certain metals become capable of superconductive propagation of electrical signals. Helium II “blood,” I realize, would indeed be an ideal carrier of nutrients through the body of a non-organic creature unable to pump a conventional fluid from one part of itself to another.
“Is that true?” Leonides asks. “Helium II? Actually?”
Gartenmeister nods. “There is no doubt of it.”
“Helium II, yes,” says Sherrard sullenly. “But it’s just lubricating fluid. Not blood.”
“Call it what you like,” Gartenmeister tells him. “I use only a metaphor. I am nowhere saying yet that they are alive.”
“But you imply—”
“I imply nothing!”
I remain silent, paying little attention to the argument. In awe and wonder I stare at the motionless creature, at the one that is moving about, and at the dissected one. I think of them out there on the Plutonian ice-fields, meandering in their unhurried way over fields of frozen methane, pausing to nibble at a hydrocarbon sundae whenever they feel the need for refreshment. But only during the night; for when their side of Pluto at last comes round to face the sun, the temperature will climb, soaring as high as 77 degrees Kelvin. They will cease motion long before that, of course—at just a few moments after dawn, as we have seen, when the day’s heat rises beyond those critical few degrees at which superconductivity is possible. They slip into immobility then until night returns. And so their slow lives must go, switching from on to off for—who knows?—thousands of years, perhaps. Or perhaps forever.