The Ocean With the Lid On

"That bright one isn't a star," Maya said. "Stars twinkle. That one's just sitting there."

Soren leaned across her to look out the window. The road was empty and dark and the heater was making its tired sound. Maya's dad was driving, half asleep at the wheel in the way that scared nobody because the road was straight for miles.

"That's Jupiter," Soren said. "My app says so." He held up his phone, then put it down because the screen ruined his night eyes.

"It has an ocean," Maya said.

"Jupiter doesn't have an ocean. It's a gas planet. There's nothing to stand on."

"Not Jupiter. One of the moons. I read it on the back of a cereal box, I think." She frowned. "Or somewhere. Europa. There's an ocean under the ice."

Soren got out the notebook. The pen was clipped to the spiral and the spiral was bent from being sat on. "That doesn't work," he said, writing the word Europa anyway. "Out there it's freezing. Way past the part where water is water. Anything that far from the sun is ice all the way through. Like an ice cube. Not an ice cube with soup in it."

"But I'm pretty sure it's an ocean."

"Pretty sure isn't a reason."

"No," Maya agreed. "But it doesn't fit. So one of us is wrong about something." She said this happily. She liked the ones that didn't fit best of all.

They sat with it. The heater wheezed.

"Okay," Soren said. "If it's liquid, something is heating it. Heat has to come from somewhere. The sun's too far. So."

"So what else makes heat."

"Inside Earth there's heat. From when it formed, and some from rocks breaking down." He tapped the pen. "But Europa's small. A little moon would've cooled off forever ago. It should be a dead frozen marble."

Maya pressed her forehead to the cold glass and looked at the bright dot that wasn't twinkling. "What's it going around?"

"Jupiter."

"And Jupiter is the biggest one. The huge one."

"The hugest. You could fit, like, all the planets inside it."

Maya went quiet. Then, "Squeeze a tennis ball."

"What?"

"When you squeeze a tennis ball over and over it gets warm. We did it in gym, the squishy grip ones. They get warm in your hand." She held up her fist and opened and closed it. "Squeeze something enough and it heats up."

Soren stopped writing. "You think Jupiter is squeezing it."

"Jupiter's gravity. It's so big. And the moon goes around and around, close and then far, close and then far." Her hand kept opening and closing in the dark. "So the pulling is hard, then soft, then hard. The whole moon gets bent. A little. Every time around."

Soren looked at his own hand. He thought about the squishy grip thing from gym, the heat of it against his palm, how it came from nothing except his own muscles working the rubber. "Bending makes heat," he said slowly. "Bend a paperclip back and forth. The bendy part gets hot. I've burned myself doing that."

"You've burned yourself on a paperclip?"

"It's a real thing. Friction. The metal fights the bending and the fight comes out as heat." He was writing fast now, the pen scratching. "So if the whole moon is the paperclip. And Jupiter bends it. Forever. Every single orbit, for billions of years."

"Then it never gets the chance to freeze solid," Maya said. "Jupiter keeps kneading it. Like dough."

"Tidal heating." Soren said the words like he was trying them on. "I think that's the name for it. The tides, but they're squeezing the inside of a moon instead of sloshing an ocean around."

"So I was right." Maya grinned. "There's an ocean."

"You were right that it didn't fit." Soren grinned back, which he didn't always do. "You were right enough."

Up front, Maya's dad said, without opening his eyes much, "You two still on the moon?"

"Europa," Maya said. "It has an ocean under the ice."

"Huh," her dad said, which was a dad's way of being asleep with his mouth.

Maya looked back out the window. The dot hung there, steady, not twinkling, and somewhere in her chest something was getting bigger than the car.

"Soren."

"Yeah."

"How much ocean. Like, how big."

He checked the phone, fast, then killed the screen. He blinked the brightness away. When he spoke his voice had gone careful. "More than Earth," he said. "More than all of it. Every ocean we have. All of them put together." He swallowed. "Twice. About twice as much water as the whole Earth."

They both stopped talking.

Maya thought about the ocean she had seen once, the actual ocean, standing at the edge where it went out past where her eyes stopped working. She thought about how that was barely half of one Earth's worth. And under the ice of that tiny bright dot, smaller than the dot of dirt on the window, there was twice all of it. Dark. Liquid. With a lid on.

"Nobody's ever seen it," she said. "The actual water. Nobody."

"No," Soren said. "It's under maybe ten miles of ice. Nobody has ever looked at it."

"So we don't know what's in it."

Neither of them said the next part. The next part was too big for the car and they both knew it sat there with them anyway, an ocean twice the size of every ocean, in the dark, warm where it had no right to be warm, and nobody had ever once looked inside.

Maya kept her eyes on the dot until the road curved and a row of trees slid up and took it away.

Soren held the notebook open on his knee so the page wouldn't close, and watched the gap in the trees, waiting for Jupiter to come back.