Jupiter's Little Moon Is Cooking From The Inside

Professor Pip patted his bulging green lab-coat pockets and pulled out a soft blob of orange clay. His crooked spectacles slid down his nose, and he pushed them back up with one paw.

"Ah! Just the thing," he said, setting the clay on the wooden lab table. Around him, Mia, Leo, and a new friend named Asha sat cross-legged in the warm amber lamplight.

"Today, my fellow scientists," Pip announced, "we're going to explore a moon that is on fire."

"On fire?!" gasped Mia.
"A whole moon?" said Leo, eyes wide.

"Precisely!" Pip's tail swished. "Its name is Io. It circles the giant planet Jupiter, and it has more erupting volcanoes than any other place we know."

He held up a striped tan-and-cream model of Jupiter, and beside it, a tiny orange model moon. "This week, a spacecraft called Juno peeked underneath Io's skin — like a doctor listening to your tummy. And guess what it heard?"

"What?" whispered Asha.

"Io is HOT beneath its surface. Much warmer than we thought. Toasty deep down inside."

Pip picked up the clay. "But why? Let's see." He began to squeeze and stretch it — SQUISH, PULL, SQUISH, PULL — rolling it fast between his paws. After a minute he held it out. "Touch it. Gently now."

Mia poked. "Whoa! It's warm!"

"Exactly right!" Pip beamed. "When something is squeezed and stretched over and over, its tiny pieces inside rub against each other. That rubbing makes heat. We call that friction."

He pointed at the model. "Now — Jupiter is enormous. So enormous that its gravity gives poor little Io a squeeze and a stretch every single time Io swings around it. Not once. Not twice. All the time. Forever."

"So Io is like a stress ball Jupiter keeps squishing?" Leo asked.

"OH MY WHISKERS! Yes, Leo! Precisely!" Pip clapped his paws. "That's called tidal heating. Jupiter's giant gravity keeps stretching Io into a slightly egg-shape, and all that squishing heats up the moon's insides until the heat bursts out — as volcanoes."

Asha's eyes went round. "So many volcanoes."

Pip looked out the window at the deepening dusk. "It's funny to think that big things nearby can change small things — even from a whole planet away. That's how the solar system talks to itself."

He handed each child a lump of clay. "Now you try. Squeeze, stretch, squeeze, stretch. Then feel."