The Squeezed Moon

The planetarium was closed but Maya's mom was running late, so the two of them sat on the floor near the gift shop while a tired man with a vacuum waited for them to leave.

"Try this," Maya said, and tossed Soren a thing from the discount bin. It was a soft rubber ball you were supposed to squeeze to relax. Soren squeezed it. He put it against his cheek.

"It's warm," he said.

"You warmed it."

"No. It got warm in my hand." He squeezed it fast, ten times, then pressed it to his face again. "Warmer. Just from squishing."

Maya took it and tried. Squeeze, squeeze, squeeze. The rubber went soft and warm in the middle.

"Huh," she said. "You're not putting heat in. You're just bending it."

"Bending it makes heat," Soren said. He liked that. He took out his notebook and the pencil moved across the page. "The rubber fights you a little every time. The fighting is the heat."

Above them, taped crooked on the wall, was a poster. Jupiter, huge and striped, and four little moons in a row beside it. Maya had been staring at one of them without meaning to.

"That one," she said, pointing with the squeeze ball. The moon was yellow and orange and blotchy, like a pizza somebody had stepped on. "Why does it look burned?"

Soren read the small print under his breath. "Io. Most volcanic place in the solar system. Hundreds of volcanoes. Lava lakes."

"Okay," Maya said. "So it's hot inside. Volcanoes need hot insides." She frowned. "But it's tiny. It's smaller than us, basically. Compared to a planet."

"So?"

"So little things cool off fast." She held the ball up. "This cooled off already. Ice cubes are small, they melt. A bathtub stays warm longer than a teaspoon. Io's a teaspoon. It should be frozen solid."

Soren stopped writing. He looked at the poster. He looked at the ball in her hand.

"Earth's hot inside because it's huge and old," he said slowly. "Leftover heat from when it formed. And the rocks down there are sort of radioactive, that makes heat too. That's the two ways. Old leftover heat, or radioactive rock."

"Io's too small for leftover heat," Maya said. "And if it was radioactive enough to do all those volcanoes, that's a lot of radioactive. The other moons are right next to it and they're not on fire."

They both looked at the poster. The four moons in a row. Io closest to Jupiter. The big striped planet hanging there like a fist.

Maya went quiet. Then she squeezed the ball, hard, once.

"Give me Jupiter," she said.

"What?"

"Pretend the ball is Io. You be Jupiter. Pull on it."

Soren grabbed one side. Maya grabbed the other. They pulled, and the ball stretched into an egg between their hands.

"Now," Maya said. "It goes around Jupiter, right? Round and round. And it's not a perfect circle, the other moons tug it off course, so sometimes it's closer and sometimes farther."

"Closer, Jupiter pulls harder." Soren pulled. The ball stretched long. "Farther, pulls softer." He eased off. The ball sprang back round.

"Do it again," Maya said. "Like the orbit. Over and over."

Stretch. Spring back. Stretch. Spring back. The man with the vacuum had stopped vacuuming and was watching two kids torture a stress ball.

Soren pressed the ball to his cheek.

"It's warm," he said. His voice had gone careful. "We did it again. The bending is the heat. Jupiter bends the whole moon. The whole rock. In and out, every orbit, forever."

"It never stops," Maya said. "As long as it's going around Jupiter, it's getting squeezed. As long as it's getting squeezed, it's hot inside. No leftover heat needed. No radioactive rock needed. Just squeezed."

"Forever," Soren said again, like he was tasting it. He wrote one word and underlined it twice. Squeezed. "It's not burning fuel. There's no fuel. Gravity does the bending and the bending never runs out."

Maya took the ball back and held it, round and warm now in her palm. She was looking at the moon next to Io on the poster. A whitish one, cracked all over like an egg.

"What's that one," she said.

Soren read. "Europa." He kept reading. He stopped.

"What."

"It says they think there's an ocean. Under the ice. Liquid water." He looked up. "It's even farther from the sun than us. Way colder. It should be a solid ice ball all the way through."

Maya was already shaking her head, slow, a smile starting.

"Same trick," she said. "It goes around Jupiter too. It gets squeezed too. Not as hard. Not enough for volcanoes. But enough to keep an ocean from freezing."

Soren put his hand flat on the poster, over Europa, the cracked white moon a billion kilometers away.

"There's an ocean," he said quietly, "and the only reason it's not ice is that Jupiter is squeezing it. Right now. While we're sitting on the floor."

"A whole ocean," Maya said. "Dark, under the ice, warm where it touches the rock. Nobody's ever seen the bottom of it."

They sat with that. An ocean kept liquid by squeezing, on a moon that should be frozen, around a planet they couldn't even see from here.

The man with the vacuum cleared his throat. "Your ride's outside," he said.

Neither of them moved yet. Maya squeezed the ball one more time and held it to Soren's cheek so he could feel it, the warmth they'd put there with nothing but their hands, the warmth that was already, slowly, leaking back out into the cold gift shop air.