Science for Kids — August 4: Craters, cosmic third wheels, and a Zimbabwe surprise

Professor Pip adjusted his slightly crooked spectacles and patted the bulging pockets of his forest-green lab coat. "Ah! Precisely what I need," he said, pulling out a shallow wooden tray, a bag of flour, a jar of cocoa powder, and one small smooth pebble.

Mia, Leo, and their friend Asha crowded around a fence post in the meadow. A big pale Moon was climbing up over the trees.

"Tonight, my fellow scientists," Pip announced, his fluffy tail swishing, "a piece of an old rocket is going to plonk right into the Moon. So the question is — what happens when something bumps into a place that has no water, no wind, and no clouds?"

"A really big BONK?" said Leo.

"Something like that!" Pip laughed. He poured the flour into the tray and dusted the top with dark cocoa. "Watch this."

He held the pebble a paw's-length above the tray and let it go. PLOP! A tiny cloud puffed up. And in the flour, a perfect round dip appeared — with pale streaks reaching out from the middle like the arms of a starfish.

"WHOA!" said Mia. "It made a mini Moon-hole!"

"Exactly right," said Pip. "That dip is called a crater. And those pale streaks are called rays — bits of stuff kicked up by the bump. When the rocket piece hits the Moon at 5,000 miles per hour, it'll blast out a crater about the size of a school bus, with rays reaching out much farther than that."

"But wait," Asha said, adjusting her glasses like Pip. "Won't the wind blow it away tomorrow?"

Pip's whiskers twitched with delight. "That's the marvelous part. The Moon has no air! No wind, no rain. Every crater ever made up there is still there. The Moon is like a giant scrapbook of every bump it's ever taken over four and a half billion years."

Leo gasped. "So the crater from tonight will still be there when I'm a grown-up?"

"When you're a grown-up, when your grandchildren are grown-ups, and long after that too." Pip looked up at the Moon, silvery and quiet. "Every dot you can see up there is a story. Tonight, we're adding one more."

He handed each child their own pebble. "Now you try. Different sizes, different heights. See what your crater looks like."

The stars were out in full sparkle. Professor Pip pulled a small brass gadget from his coat pocket — a little sun in the middle, with tiny wire arms holding a blue bead and, on an even tinier arm, a dark speck.

"Oh my whiskers, this is one of my favorites," he beamed, giving it a gentle turn. The blue bead began to loop around the sun, and the tiny speck began to loop around the blue bead. "This is called an orrery. It's a model of how things circle each other in space."

Mia stared. "The little dot is going around the bigger dot, and the bigger dot is going around the middle!"

"Precisely!" said Pip. "The middle is a star — a giant ball of hot gas, like our Sun. The blue bead is a planet. And the tiny dot… is a moon."

"Just like our Moon goes around Earth, and Earth goes around the Sun!" said Leo.

Pip's tail did a happy swish. "Exactly right. Now — until this week, every single moon anyone had ever seen was in our solar system. But astronomers just spotted a moon-shaped world way, way out among the stars, in a place called CD-35 2722. They're calling it an exosatellite — because 'exo' means 'outside,' and a satellite is anything that goes around something bigger."

"Whoa!" said Asha. "So it's a moon that isn't ours!"

"Better than that," Pip said, eyes twinkling. "This exosatellite doesn't circle a planet — it circles a failed star, called a brown dwarf. A brown dwarf is like a star that tried to switch on but never quite made it. So we have a moon, orbiting a not-quite-star, orbiting a real star. Three things dancing in a row!"

He gave the orrery another gentle turn. The three little pieces swung around each other.

"How did they see something so tiny so far away?" Mia asked.

"Very cleverly," Pip whispered. "They couldn't see the moon itself. But they could see the brown dwarf wobble. Whenever a smaller thing pulls on a bigger thing with gravity, the bigger thing shimmies a tiny bit. So the wobble told them there had to be a hidden partner — even before anyone spotted it."

Pip looked up at the stars, then handed the orrery gently to Mia. "Somewhere up there, right now, that little world is going round and round. And we just met it."

Professor Pip crouched down on the warm red dirt by the lake, pulled a soft brush and a little magnifying glass from his lab coat, and began, ever so gently, to sweep, sweep, sweep at a knobby lump poking out of the ground.

"Oh my whiskers," he whispered. "Look at that."

The lump had a shape. A curve. A bone.

Mia knelt beside him with her own tiny brush. Leo held a canvas bag ready. "What is it, Professor Pip?"

"This," said Pip, his tail flicking happily, "is a thigh bone. And not just any thigh bone. This one belonged to a dinosaur who took a nap here… two hundred and ten million years ago."

Leo's eyes went as big as saucers. "TWO HUNDRED AND TEN MILLION?"

"Precisely," said Pip. "That was a time called the Late Triassic. Dinosaurs had just started to spread across the whole world. And this fellow — scientists are calling him Musango, which means 'living in the bush' — was a young one. About your age, in dinosaur years."

"How can you tell how old he was?" asked Mia.

"Because bones grow like tree trunks," Pip whispered. He drew a circle in the dirt and added rings inside it. "Every year a dinosaur was alive, its bones added a new ring. If you cut a bone open — very carefully, of course — you can count them. Just like tree rings. This little one had about eight."

"How big was he?" Leo asked.

"About the length of a car. And he was a sauropodomorph — the great-great-great-great-grandparent kind of dinosaur that would one day grow into the enormous long-necked giants, some as long as three school buses lined up."

Mia looked at the little thigh bone. "So he was a baby giant?"

"A young cousin of the giants," Pip said. "For 210 million years, this bone waited here for someone to come and say hello. And today, my fellow scientists, that someone is us."

He handed Mia the little brush. "Sweep gently. Every fossil is a message from a very, very long time ago."