Io's tidal heating 🌋

"Perhaps if Io can be understood, so too can our moon —as well as several of the other satellites in our solar system with hidden tidal engines.

"For now, this volcanic orb remains maddeningly inscrutable. Io’s a complicated beast, Davies said. The more we observe it, the more sophisticated the data and the analyses, the more puzzling it becomes.

"Our own moon shows evidence of primeval tidal heating, too. Its oldest crystals formed 4.51 billion years ago from the stream of molten matter that got blasted off Earth by a giant impact event. 

"But a lot of lunar crystals seem to have formed from a second reservoir of molten rock 4.35 billion years ago. Where did that later magma come from?

"Nimmo and co-authors offered one idea in a paper published in Nature in December: Maybe Earth’s moon was like Io. The moon was significantly closer to Earth back then, and the gravitational fields from the Earth and the sun were battling for control. At a certain threshold, when the gravitational influence of both were roughly equal, the moon might have temporarily adopted an elliptical orbit and gotten tidally heated by Earth’s gravitational kneading. Its interior might have remelted, causing a surprise secondary flourish of volcanism.

"But exactly where within the moon’s interior its tidal heating was concentrated —and thus, where all that melting was happening —isn’t clear."