A vibration came up through the tunnel floor. It wasn't the drill bit. Jaeyoung shut off the drill and stripped off his glove. The inside was damp with sweat. He laid his palm flat on the floor. A faint trembling spread across the skin of his bare hand. His left arm felt nothing. From below the elbow to the fingertips it was a neural prosthetic, fitted three years ago. He'd lost his left forearm in a mining accident and taken this in its place. The prosthetic relayed only pressure and temperature. Vibration lay outside its range. Jaeyoung read the trembling of the floor with his right hand alone. It wasn't regular. It didn't match the rotation period of Asteroid 4401 Andra, and it didn't match the working rhythm of the mining rigs either.
The interior lamp of his helmet lit the tunnel wall. A black crystal had surfaced there. It hadn't been there yesterday. Jaeyoung drew the sample hammer from his belt and struck the edge of the crystal. The instant the hammer met the surface, the prosthetic on his left arm convulsed. All five fingers splayed open at once, then clenched shut. Jaeyoung lost his grip on the hammer. It fell to the tunnel floor with a ringing of metal. He stepped back. The prosthetic's status light had turned yellow. A fault signal.
Jaeyoung slowly raised the prosthetic arm and looked at it in front of his face. The helmet lamp glinted off the artificial skin. The fingers were trembling. The prosthetic's synthetic muscle fibers were contracting and relaxing, over and over. Not by his will. When he tried to move a finger, the response came 0.3 seconds late. Something was interfering with the prosthetic's neural interface. Jaeyoung looked at the black crystal in the tunnel wall. At the point the hammer had struck, a fine dust hung in the air. Asteroid 4401 had no magnetic field. An environment less than one hundred-thousandth of Earth's. And if, in that environment, this crystal held a magnetism.
Jaeyoung came out of the tunnel and made his way back to the base module. The fluorescent light in the corridor flickered. The whir of the oxygen recirculator's fan filled the passage. He opened the door of the infirmary. Gihyeon was inside. The base's medical officer. He sat before a monitor, studying the supply-ship schedule.
"Take a look at the prosthetic."
Gihyeon turned his head. His eyes narrowed at the sight of Jaeyoung's left arm. The fingers were still trembling, irregularly.
"Since when?"
"Twenty minutes ago. Since I put a hammer to a new mineral down in the tunnel."
Gihyeon took a diagnostic cable from a drawer. He opened the port cover and connected the cable to the prosthetic. A short connection tone sounded. The neural interface's signal waveform came up on the monitor. Gihyeon's hands went still over the keyboard.
"What is this."
The waveform on the screen had climbed past the normal range. The prosthetic's neural interface worked by reading the electrical signals from the residual nerves to move the artificial arm. But the amplitude of the waveform was three times the output of the residual nerves. A signal was coming in from outside.
"What did you touch down there?"
"A black crystal. I think it's magnetic."
Gihyeon magnified the waveform. The frequency of the external signal was constant. 7.3 hertz. A range that overlapped the natural frequency band of human nerves.
Jaeyoung sat in a chair and looked at the ceiling. Cold air came down from the vent overhead. The trembling in his left arm changed. The fingers no longer convulsed. Instead something began to register across his whole palm. A sensation that was neither pressure nor temperature. Jaeyoung opened his left hand and looked at the palm. The sensors beneath the artificial skin were responding. But what they were reading wasn't physical contact. The prosthetic was sensing something coming off the air of the infirmary, the walls, Gihyeon's body.
"I feel something with my left hand."
Jaeyoung said. Gihyeon looked around.
"Feel what?"
"I don't know. But my left hand knows you're sitting over there. I think I'd know even with my eyes shut."
Gihyeon rose from his chair. He stepped a pace away from Jaeyoung. Jaeyoung closed his eyes. The sensation in his left hand shifted. He felt Gihyeon's presence receding. Not a distance—more like a density. The feeling of the weight a person occupies in space growing lighter.
"You just moved back."
Jaeyoung said, eyes still shut. Gihyeon didn't answer. Jaeyoung opened his eyes. Gihyeon stood two meters behind him. Wariness had surfaced on his face.
Jaeyoung went back down into the tunnel. Alone. The black crystal was drinking the light from the tunnel wall. Where the helmet lamp touched its surface, the light vanished. A material that absorbed without reflecting. Jaeyoung brought his ungloved left hand near the crystal. Thirty centimeters. Twenty. Ten. The prosthetic's sensation grew stronger. Something was flowing out of the crystal. A magnetism that could exist only in an environment without a magnetic field. A property that would collapse the instant it entered Earth's field. A substance made by this asteroid's vacuum and its fieldless dark.
His left hand touched the crystal. The sensation detonated. Jaeyoung's vision swam. The strength went out of his knees. Inside the helmet his breathing quickened. He couldn't see the tunnel wall. Instead he saw the structure within the wall. No—he wasn't seeing it. His left hand was feeling past the wall. The density distribution of the rock. The direction of the vein along which the crystal ran. A cavity 140 meters below the tunnel floor. All of it unfurled through the sense in his left hand. Jaeyoung's right hand grabbed the tunnel wall. His knees gave. His heart pounded fast. His breath went shallow.
The sensation subsided 40 seconds after he took his hand away. Jaeyoung was slumped on the tunnel floor. Inside the helmet his breathing was ragged. The faceplate had fogged over. The prosthetic on his left arm was hot. The artificial muscle fibers were 12 degrees above normal. The cooling circuit was throwing an overload warning. Jaeyoung cradled the prosthetic arm against his chest and waited. It took 6 minutes for the temperature to come down. In the meantime he pressed his left arm to the cold rock of the tunnel floor. Through the artificial skin the chill of the rock seeped in.
Back at the base, Jaeyoung gathered his sample tools and went down into the tunnel again. He broke off a shard of the crystal. Fist-sized. He sealed it in a container. As he made his way out of the tunnel his left arm was pulled toward the container. Like a magnet drawing it, but not quite. The prosthetic's neural interface was aligning itself toward the crystal. His fingers spread open toward the container. Jaeyoung caught his left hand with his right.
In the base's analysis lab Jaeyoung measured the crystal's basic properties. Density 7.2. Hardness on the order of diamond. Electrical conductivity zero. Magnetic susceptibility beyond the range of the instrument. The analyzer's magnetic sensor read saturated. Jaeyoung saved the results and went to the comms module. The lag to Earth was 34 minutes one way. Jaeyoung transmitted a report to the company's mining management division. New magnetic material discovered. Property data attached. Sample secured.
The reply came 68 minutes later. A short text. Load the sample onto the next supply ship. Property data confirmed. Additional sampling recommended. 14 days until the supply ship arrived. Jaeyoung read the reply and shut off the comms module. He went to the infirmary. Gihyeon was analyzing the prosthetic's logs.
“The receptors in the neural interface are deforming.”
Gihyeon turned the monitor so Jaeyoung could see. The receptors' microstructure was on the screen. The structure at the time of installation and the current structure sat side by side. The surface pattern had changed. The receptors had rearranged themselves in response to the crystal's magnetic signal.
“Does this go back to normal?”
Jaeyoung asked. Gihyeon shook his head.
“The structural change is irreversible. And it'll go further with more exposure to the crystal. If you take the prosthetic off at this stage—”
Gihyeon stopped.
“If I take it off?”
“The interface deformed while it was bonded to what's left of your nerves. Detach the prosthetic and you damage the receptors on those residual nerves too. The sensation your left arm still has—pressure, temperature. You lose that too.”
Jaeyoung left the infirmary and went to his quarters. The room was 2 meters by 3. A bed and a personal locker. Jaeyoung sat on the bed. He lifted his left arm. Under the fluorescent light the prosthetic's artificial skin was a pale gray. He tried moving the fingers. The response had returned to normal. But a faint sensation lingered in his palm. Gihyeon beyond the wall, the oxygen recirculator in the corridor, the vacuum past the bulkhead. All of it registered dimly in his left hand.
Jaeyoung took the sealed container from the locker. He opened the lid. The crystal drank the fluorescent light of the room with its black surface. The air around it felt cold. Jaeyoung laid his left hand over the crystal. The sensation surged in. Sharper this time than in the tunnel. The wall structure of the quarters. The empty bed in the next room. The distribution of rock across the asteroid's surface beyond the base's outer wall. Farther. The curvature of the asteroid. The angle at which the solar wind grazed its surface. His left hand was sensing the whole asteroid. Its mass and shape and inner structure fused into a single sensation. A sensation no language could hold. Jaeyoung's mouth fell open. His breath stopped. 3 seconds. He exhaled. He took his hand away.
The next day Jaeyoung descended into the deep tunnel. The cavity 140 meters down. The crystal sheathed the entire wall of the cavity. The black crystal swallowed his helmet light, and inside, that light alone wasn't enough even to make out the floor. Jaeyoung pulled off his glove. He reached out his left hand. He didn't need to touch the crystal—the density of it inside the cavity was enough. The sensation opened not in breadth but in depth. Past the asteroid's surface. The rock fragments in nearby orbit. The vacuum beyond them. Something was in that vacuum. His left hand was reading it. Jaeyoung couldn't tell what it was. But his left hand knew its position, its size, its density.
Jaeyoung spent 3 hours in the cavity. When he came out, the sensation in his right hand had gone dull. Next to his left, his right felt gloved. Next to nothing at all. The more his left hand opened onto the world, the more his right hand closed. Jaeyoung ran his right hand over the tunnel wall. The rough face of the rock. The temperature. Ordinary touch. But against what his left hand took in, the sensation in his right hand was pitifully thin, almost a lie.
Gihyeon checked Jaeyoung's prosthetic logs again. The receptor deformation was progressing. The interface's sensing range was widening. Gihyeon said,
“When the supply ship comes, put the sample on it and go too. You need to see a prosthetics specialist on Earth.”
Jaeyoung didn't answer.
“Did you hear me?”
“Does this sensation hold up on Earth too?”
“No. Earth's magnetic field changes the crystal's properties. Inside a magnetic field this material is just a rock. Nothing for the prosthetic to read.”
“Then what's left for me?”
Gihyeon looked at him.
“A deformed interface. A prosthetic whose original function is damaged. You'd need corrective surgery on Earth. If the surgery even works.”
Jaeyoung opened the sealed container in his quarters and touched the crystal. Every night. He killed the light, lay on his bed, and set the crystal on his left hand. In the dark he had no need for eyes. His sense deepened. On the third day he could draw the entire layout of the base with his left hand. On the fifth day he detected the distribution of impact craters across the asteroid's surface. On the seventh day he felt the solar panels outside the base, orbiting the asteroid, trembling faintly in the solar wind. The sense in his right hand grew duller and duller. Next to the world his left hand revealed, his right hand might as well have had its eyes closed.
Three days before the supply ship was due, Jaeyoung went back down to the cavity deep in the shaft. He laid both hands against the crystal wall. The sense in his left hand opened. Beyond the asteroid, out in the vacuum, that thing registered again. This time the outline was sharp. It was moving. Toward the asteroid. Jaeyoung's heart sped up. His left hand read its size. A third of the asteroid. Big enough that if it hit, nothing of the base would be left. He couldn't run the orbital math. But his left hand was feeling its speed and its heading. Jaeyoung burst out of the cavity.
The base control room. When Jaeyoung opened the door, Sujin was there. She had the night shift for orbital monitoring. Three screens displayed the orbital data around the asteroid.
"Sujin. There's something out past the scan range."
Sujin turned around.
"Past the range? The scan reaches 200 kilometers. Anything beyond that, we don't pick up."
"There's an object a third the size of the asteroid, coming in from beyond 200 kilometers."
Sujin's eyes narrowed.
"And how do you know that?"
Jaeyoung raised his left hand.
"I felt it. With this."
Sujin looked at his prosthetic arm. Under the artificial skin, the sensor lights were blinking in an abnormal pattern. Heat was rising off his fingertips. In the cold air of the control room, the prosthetic's warmth was throwing off a small shimmer. Sujin took a step back.
Sujin pushed the orbital scan range to its maximum. 200 kilometers. 300. 400. She forced the resolution down and scanned all the way to 500. Nothing came up. It was the scanner's physical limit. Sujin sank back against her chair.
"Send an emergency transmission to headquarters," Jaeyoung said.
"Saying what? That you felt it through your prosthetic?"
There was an edge to Sujin's voice.
"If I tell them a prosthetic caught something the instruments can't, what do you think headquarters is going to say?"
Jaeyoung sat down in the chair next to hers. He rested his left hand on the monitor. Through the surface of the screen, the base's electronics registered. Past them, the asteroid's surface. Past that, the vacuum. The object was still coming.
"72 hours," Jaeyoung said. His voice was dry. "It gets here inside 72 hours. From the collision angle, it won't hit the base directly. But I don't know if the bedrock will hold."
Sujin swung her chair around and looked at Jaeyoung. His left arm lay across the monitor. The fingers were trembling faintly. Sujin opened her mouth, then shut it. She looked back at the screen. The orbital scanner's data was still clean. No threat.
Jaeyoung left the control room and went down into the shaft. The deep cavity. He set his left hand against the crystal wall. He checked the object's position again. It had come closer. Jaeyoung didn't lift his hand from the crystal. His left hand read the asteroid's internal structure. Eighty meters below the cavity there was a larger space. Not crystal—hollow. A structural weak point in the asteroid. When the impact came, the asteroid would split right there.
Jaeyoung pulled his hand away. His palm was flushed with heat. The prosthetic's cooling circuit gave a warning tone. Jaeyoung ignored it and climbed back up the shaft. He went to find Gihyeon.
"How much longer will the prosthetic hold?"
Gihyeon checked the logs.
"The cooling circuit is maxed out. Three more overloads and the interface burns. Along with the nerve that's left."
"And if the nerve that's left burns?"
"Total, permanent loss of all sensation in the left arm. And you can't fit another prosthetic. Once the nerve endings are gone, there's no tissue for a new interface to bond to."
Jaeyoung went back to his quarters. He sat on the bed. He looked at his left hand. Under the artificial skin the sensor lights blinked in a steady rhythm. Lose this sense, and the unseen world closes back up. Keep it, and the last of the nerve burns away. When the supply ship arrived, he was supposed to load the specimen and head for Earth. Inside Earth's magnetic field the crystal would lose its magnetism, the prosthetic would have nothing to read, and only the deformed interface would be left. Stay on the asteroid and the sense held, but the prosthetic would be destroyed. Whichever he chose, his left arm was not coming back.
Jaeyoung opened the sealed container. He took out the crystal. He set it on his left hand. The sense opened. The object had drawn closer. 48 hours. Still holding the crystal, Jaeyoung went to the control room. Sujin was in front of the monitor. Gihyeon was there too.
"The scanner caught something," Sujin said. A faint dot hung at the edge of the screen. Sujin looked at Jaeyoung. Her lips were pressed tight.
"You were right. I'll run the orbit calc."
Gihyeon started calculating the object's trajectory.
Jaeyoung sat in the control room chair, holding the crystal. Her left hand read the object's orbit. The impact point. Surface terrain 4 kilometers from the base. Not a direct hit. But the shockwave would bring down the hollow beneath the cavity. The bedrock the base stood on would split. The modules would lose their seal. Jaeyoung let go of the crystal. The prosthetic's cooling alarm sounded again.
"We have to move the base."
Jaeyoung said. Gihyeon and Sujin turned.
"The impact point isn't a direct strike. But there's an empty space 80 meters down. If the shockwave collapses it, the base sinks."
Sujin asked.
"And how exactly do you know that."
Jaeyoung raised her left hand. Heat was pouring out of the prosthetic's cooling circuit.
Three days until the supply ship arrived. 48 hours until the object did. The base modules were bolted to the surface. The dismantling gear needed to move them was on the supply ship. Relocating the base was impossible. Only evacuation was possible. Jaeyoung gripped the crystal again. The cooling alarm sounded in one long string. Second overload. One use left. Her left hand read the object's exact angle of impact. Read the direction the shockwave would travel. Read which sections of the base would collapse and which would remain. Jaeyoung let go of the crystal. The prosthetic arm was too hot to hold against her chest. She let it hang at her side. Heat rose off the surface of the artificial skin. Jaeyoung touched the left arm with her right hand. The texture of the artificial skin had gone rough. The heat had subtly warped the surface.
"The safe zone is past bulkhead 3."
Jaeyoung said. Gihyeon looked at Jaeyoung's prosthetic. The sensor light had gone red.
"One more time and it's done."
Gihyeon said. Jaeyoung didn't answer.
14 hours later, Sujin's orbit calculation was finished. Impact point: 4.2 kilometers from the base. A 200-meter difference from what Jaeyoung had read with her left hand. Sujin looked at Jaeyoung.
"I sent the supply ship an emergency message. Asking whether they can move up their arrival."
Gihyeon opened the base's internal comms. All personnel evacuate. Past bulkhead 3. Voices overlapped on the channel. Questions, protests. Gihyeon answered them one by one. Past bulkhead 3. The safe zone Jaeyoung had read with her left hand.
When the evacuation was complete, Jaeyoung stood in front of bulkhead 3. Gihyeon's voice came from the other side.
"Come inside."
Jaeyoung laid her left hand against the bulkhead. Just once more, one last time. The people beyond it. Gihyeon, Sujin, the other 5 — their body heat, their density, their positions unfolded across her left hand. The structure of the whole asteroid opened one more time. The object would arrive in 18 hours. The path the shockwave would travel. Bulkhead 3 would hold. Jaeyoung's left hand was certain of it. It was the last thing the left hand ever read.
The cooling circuit gave its final warning tone. Something inside the prosthetic smelled of burning. Heat seeped out between the seams of artificial skin. Jaeyoung pulled her hand away. All sensation in the left arm vanished. Pressure, temperature, the senses the crystal had opened — all of it. Nothing. Jaeyoung tried to lift the left arm. The fingers wouldn't move. The sensor light was dead. Jaeyoung took hold of the left arm with her right hand and opened the bulkhead. She stepped inside. Gihyeon looked at Jaeyoung's left arm. He said nothing. The bulkhead closed. Somewhere in the shaft beyond it came the sound of rock splitting. The asteroid's tremor was climbing up through the soles of her feet.
