Listen to the audio version

The boy sat cross-legged in the middle of the floor, chanting names: Metis, Adrastea, Amalthea, Thebe . . . He said them to calm himself. His Mom had told him, "Facts fight fears."

He climbed into Dad's chair by the communication console and surveyed the buttons, toggles, sliding switches, small joysticks and an array of lights. Some blinked, some were green. One was red. A countdown timer clicked off numbers methodically: "0D, 2H, 12M, 8S." The 12 became 11 while he watched.

He pressed a button. His Dad always pressed buttons when he sat here. "Ethan to Dad and Mom," he said. The speaker above a small video screen that displayed nothing remained silent. Ethan tried his call again. Dad made calls too, except he said, "Captain Ramis to Relay Central," to talk to his bosses, or "Base to Mobile One," when he called Mom. She said the same thing when she sat in that seat, but she'd be calling Dad. Someone always answered when they called. Mobile One would answer on its own if Mom and Dad were in the habitat. It could explore independently. "It has a bright AI," Dad said.

But no one answered. He was sure he pressed the right button. He'd seen Mom and Dad use it a thousand times, but they also adjusted dials before making a call. He didn't know what the settings were. He murmured, Io, Europa, Ganyemede, Calisto.

Through the tiny port beside the communication array sat Mobile One, eighty yards away on Io's uneven surface. Something had happened to it: The six-wheeled car was canted to the side, lying on its single door, the top pressed to a rock, crushing the communications array. "Ethan to Mom and Dad," he said again. "Are you okay?"

Behind him, Mom had hung a "Happy Birthday" banner over the dining room table. She and Dad had been figuring out how to make a cake for him before they'd left. They'd wrapped a present that sat in the table's middle. "I'm five today," thought Ethan. "Today's my birthday." Mom would hold him close and call him her "little miracle." Dad bounced him on his knee when he sat at his workstation. He played games with him. He read to Ethan and said he was their "science project." He said, "You, my child, are a 'misappropriation of resources,'" then laughed and hugged him.

"Station, why aren't they answering?"

The station said, "The Mobile One Rover appears to be incapacitated."

"What it they're hurt?"

"My medical facility is top notch. It can print skin, major organs, eyes, and other desired replacements. It can also diagnose and treat most known illnesses."

"Call Relay Station. They'll help."

"Relay Station will not be within range for four more days. You will have to be brave."

"Shut up, Station." Ethan hated AI pep talks. It was always telling him to work hard or be happy or to "solve the problem."

Ethan went back to the port. In the distance, one of Io's numerous volcanoes spewed sulfur dioxide into the sky. Sunlight caught the flume, turning it into a sparkling fountain.

If he could call Relay Station himself, he would, even though Mom and Dad warned him to never talk to them. They sent him from the room when they called. "They don't know about you," said Mom. She told him when he went to bed about their journey to Io, about how they were to man the station for seven years before coming home. "We were too lonely," Mom said, "So you came along. You're our secret child. You're a treasure and twice as precious."

Ethan checked the countdown timer again. 0D, 2H, 7M, 49S. It was the air supply in Mobile One.

"Are they okay? How's their telemetry?" No one told Ethan that he had a strange vocabulary for a five-year old. In fact, it wasn't unusual for someone raised the way he was. He knew words like silicate, caldera, Colchis Regio, and he knew that Io was subject to tidal heating. He could disassemble and reassemble a space suit, and he could sort and store rock samples. He could name Jupiter's sixty-three moons.

"No telemetry data is available from Mobile One."

"Is there air in the rover? Has it ruptured?" Ethan swallowed heavily. He knew about vacuums. He understood that outside the habitat was beautiful but empty and deadly cold. Jupiter filled half the sky, white, grey and orange striped, always changing and always huge.

"No telemetry data is available from Mobile One. Your parents wear space suits when in the rover, though. Even if there were a loss of pressure, they could survive."

Ethan grabbed handholds and propelled himself through the living area and work area, barely touching the floor in the light gravity, past hydroponics and the power plant until he was in the garage. Mobile Two stood under the lights, a duplicate of the rover marooned outside the station. Access covers were open. Wires led to panels on the walls. "Can we fix Mobile Two?" said Ethan.

"It has no AI," said Station.

"I don't need it to be smart. Can we drive it?"

"The AI controls the complicated gearing in the wheels, adjusts life support, and is the coordinator for all mechanical operations. Without the AI, the rover cannot be operated safely."

Ethan climbed up the vehicle's side to the cabin. "We're only going to Mom and Dad."

Inside the vehicle were two rotating seats and numerous control panels. Mom and Dad took him for rides many times. They used one set of controls to drive it and another manipulated the mechanical arms on the front and back. Once, Mom let him move the arms. He had stretched them out from the rover, opened their clawed hands, and dragged them through the sulfur dioxide frost that covered the surface.

"Is this strong enough to set Mobile One upright?"

Station said, "Mobile Two suffered damage in a quake five years ago. It cannot maintain cabin pressure. It cannot be operated safely without the AI. You will not be able to control it efficiently to effect a rescue. This line of questioning is not brave; it is foolish."

"Tell me how to get Mobile Two ready to move."

The Station didn't answer.

"Don't be such a baby!" yelled Ethan.

Ethan tried not to imagine that he was already too late. Dad told him once while they were doing one of their regular safety inspections, "The universe doesn't forgive mistakes." They had been checking the motion dampers the station rested on. If one failed, any of Io's regularly occurring, strong quakes could shake the station to pieces. "Io is like a big ball of putty," Dad said. "Jupiter's gravity and the other moons squeeze and pull on it all the time. The surface rises and falls more than a hundred yards per cycle. It's like being in an elevator."

Maybe Mom and Dad had made a mistake.

Themisto, Leda, Himalia, Lysithia. Ethan detached power cables like he'd seen his parents do before. The heavy connectors were hard for him to budge. He had to grip with both hands, brace a foot against Mobile Two and pull.

"How much time, Station?"

"One hour, twenty-one minutes. I have run diagnostics on Mobile Two. The cabin may not hold air. The heating units are off line. The vehicle has not moved on its own power for one-thousand, eight-hundred and twenty-five days."

Ethan ran around the rover, disconnecting wires and closing panels. "Is it strong enough to push Mobile One off its side?"

"Yes . . . probably, but, Ethan, if you lose your air and freeze, you will not have saved anyone. Your parents will not approve of you doing this."

"What I need is a spacesuit that fits."

"One does not exist."

"Can you help me drive Mobile Two?"

"I can remotely monitor rover status. I can answer questions." The speakers whispered. Station hadn't finished talking but was deciding how to phrase its thought. "If you leave, I will be lonely."

Ethan worked grimly, silently. Station sang songs to him at night, read him poems, played word games. When Mom and Dad worked, Station was his friend. It cheered him when he was sad.

Station said, "If the cabin loses pressure, the liquids in your skin will boil away, lowering your temperature precipitously. This will be painful. The garage depressurizes in sixty seconds. It repressurizes in five minutes. A human being loses consciousness in fifteen seconds in a vacuum."

"If you can't be helpful, stop talking." Ethan opened a locker, pulled out a reflective blanket and tossed it into the rover.

Elara, Carpo, Euproie, Thelxinoe. The chanting quieted his breathing. He circled the rover. All the cables and wires were detached. The pathway to the garage door was clear. He started to climb the ladder, then jumped off and ran back to his sleeping area. In his toy box, he found the six-inch tall astronaut his parents had printed for him. Mom called it an "action figure." The miniature stood resolutely with his feet apart, hands on his hips, looking up as if he expected to rise on his own in a moment. Ethan called him Alpha-man. Alpha-man explored new planets, he made friends with alien creatures (Mom and Dad had printed them too), and Alpha-man always knew what to do. Mom told him Alpha-man adventures before he went to bed.

Ethan put Alpha-man on the mission specialist seat in the rover, while he fastened himself into the pilot's seat. A push of a button, and the door closed with a pneumatic finality, popping his ears as the cabin established its own pressure. He threw a switch that turned the garage lights to flashing red. Air rushed from the space. At first the pumps sucking the air away sounded loud. Then the noise faded. Ethan listened intently. Was there a hiss? Of all the sounds on the habitat, leaking air was the one he feared most. Twice he'd discovered leaks after large quakes. As powerful as the motion dampers on the station were, a heavy shaking strained the structure. Doors automatically closed to isolate compromised areas. Mom and Dad sprinted to make repairs. In every room, sealant and patching material stood ready.

The panic always started with a hiss.

No hiss. Just steady fan noise. The garage doors opened outward, revealing Io's dim surface. Dad told him that the sun lit Io's surface about the same brightness as on Earth right after the sunset. Ethan had seen pictures of Earth. The sun's brightness during the day didn't look as weird to him as a sky without stars or Jupiter's looming presence.

Controls on Mobile 2 were straightforward. One joystick steered while the other changed speed. The AI adjusted power to the wheels depending on the traction. Mom told him that driving across Io was like navigating a field of concrete bubble wrap. Lava flow created the moon's surface. Gas-filled cavities and lava tubes formed beneath the elastic rock before cooling, some very thick, but some parchment thin. Broken bubbles, like cracked egg shells, scattered across the plain, monstrous gaping holes rimmed with silicate rock, iron and iron sulfate teeth.

"How much time?"

"Thirty-seven minutes."

Euantha, Helike, Orthosie, Locaste.

Ethan slid the joystick forward. Electric wheels clicked into motion; the rover lurched and then stopped.

Station said, "You must continue to press the joystick forward or Mobile Two will halt. I'm detecting a slight air leak in the cabin. The rover will automatically compensate by pumping in more air."

Ethan felt good. He was three feet closer to rescuing his parents, seventy-nine yards to go, so he pressed the joystick, following the path Mobile one had taken.

"Why did they fall over? They've driven this way a thousand times."

"Without readings, I would guess an undetected sinkhole."

The rover cleared the garage doors, jerking forward, allowing Ethan to see more of Io than was visible from the habitat. A second volcano sprayed beyond the horizon, marking Jupiter with a silver haze.

He wrapped the blanket tightly around his shoulders. Without heating units, the air that blew into the cabin was already cold. Beyond that, the heat he carried with him quickly dissipated. His breath blew out in frost.

"Your air leak is increasing, Ethan." Station sounded desolate.

A slight whistle sounded from the door, and the blowers redoubled their efforts, but Mobile Two advanced steadily. Now, it was only twenty yards away. He saw a light from Mobile One's cabin that he hadn't been able to see before. It glowed on the rock the rover had fallen against, so it still had power. The wheels on the left side had broken through the brittle surface. What had been a level path yesterday now had a pothole large enough to tip Mobile One.

The whistle raised in volume. Ethan swallowed to clear his ears. Praxidike, Harpalyke, Mneme, Hermippe.

Ten feet from the crippled rover, Ethan slowed Mobile Two. He gasped a little for breath, and he realized his nose was bleeding. His face and hands had lost feeling. The forward arms took a minute to unship. At first, they wouldn't move. Ethan shoved the control forward that should have extended them, but they only whined. Then he remembered and threw a toggle that released them. A heavy thump from the rover's roof told him they were free.

"If you lose air pressure, you will have fifteen seconds of consciousness," said Station.

Ethan maneuvered the arms so he could scoot them under the fallen rover. "That is not helpful." He wished there was a window in back that he could see through. Were his parents okay? If he could right the vehicle, and the door wasn't jammed shut, they could walk to the habitat. Dots swam in front of his eyes. He tapped the joystick that moved Mobile Two forward. The hands slid through the yellowish frost, under the metal. He pulled the lever back. If the hands held, if Mobile One wasn't too heavy, if his parents were alive, this could work.

Servos inside whined in protest. The arms were designed for medium to light tasks, like collecting samples or moving rocks, not picking up an entire exploration vehicle.

Station said, "Oh, no. Be brave."

With a pop, an entire section of seal around the door gave way. A whirlwind stirred dust and a scrap of paper. Alpha-man flew off the mission specialist's chair. Stuck to gap in the door for a second, then fell. Twin ice picks jammed into Ethan's ears. He screamed but couldn't hear it as his lungs emptied themselves. No air came in when he inhaled. His eyes burned. Bubbles formed on the backs of his hands. Everything in him shrieked with pain, but Mobile One stirred! Ethan held the joystick back. His face, his arms, all of him seemed to swell.

Fifteen seconds is what Station said. Slowly Mobile One tipped toward upright. Time slowed. Surely fifteen seconds had passed, but he could still see what was happening. Ice crystals formed in his mouth and nasal passages. Pain. Pain. Pain. He held on. He held on.

Thyone, Ananke, Herse . . .

A flicker. . .

He dreamed.

Mom leaned over him.

Aetne, Kale, Tygete . . .

I'm awake, he thought.

A flicker. . .

Dad examined Ethan's arm. "His skin is freeze dried. Muscles ruined." Dad pulled on the skin. It flaked away. Broke off in chunks. Ethan felt nothing.

A flicker . . .

His arms were naked metal rods that ended in shiny metal skeleton hands. Ethan couldn't move.

"We'll reprint the damaged parts. We can build him again."

Mom said, "Is the AI intact? Is he still Ethan?" She looked down on him. Ethan tried to show her that he was there, but nothing moved. He couldn't even blink.

Dad thought for a moment. "I think so. A rover's AI is built for abuse. A freezing wouldn't wipe it clean."

Ethan saw Mom's hand coming down. She must be touching my head, he thought.

"So he'll still be my little boy?"

Dad smiled. "Far as I can tell. He's come a long way from being a wiped rover AI."

Station said, "He's not dead? You can make him again?"

Mom and Dad nodded.

Station sobbed.