A peanut-shaped asteroid that just can't spin straight

Professor Pip pushed his crooked spectacles up his nose and patted his bulging green coat pockets. "Where is it… ah-HA!" He pulled out a small peanut, still in its shell, and held it up. From another pocket came a smooth, round acorn. From a third — his small brass telescope, gleaming gold in the lantern light.

A few children sat in the soft grass at the top of the hill. The sky above them was slowly turning purple, and the first stars were just beginning to wink awake.

"Tonight," Professor Pip announced, his bushy tail swishing, "we're going to learn about an asteroid named Donaldjohanson — and why it can't seem to spin straight!"

"Donald-who?" giggled Leo, scrunching his nose.

"Donaldjohanson!" Pip repeated, beaming. "He's a real chunk of space rock — about as long as a city. NASA sent a spacecraft called Lucy zooming past him to take a peek. And what Lucy found was very strange indeed."

He held up the smooth acorn. "Most asteroids are roundish, like this — they spin nicely, around and around." He gave it a twirl on his paw. The acorn whirled smoothly.

Then he held up the peanut. "But Donaldjohanson looks like THIS — two bumps connected by a skinny middle, like a peanut in its shell!"

He gave the peanut a flick. It tumbled wildly across the grass — over, around, over, around — wobbling end over end. The children gasped and laughed.

"Why does it wobble?" asked Mia, eyes wide.

"Precisely the right question!" said Pip. "When an object has two lumps far apart, it can't spin smoothly. It tumbles — like trying to spin a pencil and a basketball glued together. That tumbling motion is called rotation, and a wobble like Donaldjohanson's is what scientists call a complex rotation."

He held up his pocket notebook. "Lucy clocked Donaldjohanson rolling end-over-end once every ten and a half Earth days, AND wobbling sideways once every twenty-six and a half days. Two wobbles at once!"

"Like when I try to spin a banana!" Leo blurted.

"Exactly right!" laughed Pip. "Curiouser still, scientists think Donaldjohanson is two old broken pieces of an even bigger asteroid that drifted back together long ago. The two lumps are the two pieces — gently stuck by their own gravity."

He looked up at the glittering stars. "Imagine that. A whole little world, broken and rejoined, tumbling quietly through space for one hundred and fifty-five million years."

He pressed the peanut into Mia's paw. "Now you try. Find anything in your kitchen that's lumpy and uneven — a banana, a pretzel, a spoon — and give it a spin. Watch how it wobbles. That's the same dance Donaldjohanson does, just a billion times slower."