NASA image of the Kopff Crater in the moon's Orientale Basin

The moon used to spin out of control, and it was pretty hardcore

Contributed by
Feb 27, 2018

When you look up at the moon, it’s hard to believe this mystical glowing orb floating among the stars was once in the throes of chaos.

The craters and basins that scar our satellite’s rocky surface betray a violent past. Postdoctoral researcher James Tuttle-Keane of Caltech revealed to Astronomy Magazine that even minor asteroid hits can throw the moon’s spin off, while the monster crashes that left behind impact basins (craters over 100 miles in diameter) affected everything from its magnetic field to its geology and otherwise gave it a cosmic thrill ride.

“One of the most dramatic ways a planet’s spin can change is via impacts. Impacts change the planet’s angular momentum, energy, and moments of inertia,” Tuttle-Keane said in a study presented to the American Astronomical Society. “These changes can have important consequences for the geology of the planet.”

Objects hurtling through space have their own angular momentum — the product of their moment of inertia and angular velocity — which they transfer to anything they slam into. They also pass on a slight spin with that angular momentum. As if that isn’t enough, material from the moon’s surface and mantle would scatter into space during the massive asteroid collisions that formed its largest impact craters. That material would then rain back down on the moon and redistribute its mass. Add mass redistribution to impact trauma, and you have a moon that would would have been wobbling nonstop if you were observing it from Earth 4 billion years ago.

NASA image of the moon's Orientale basin

The moon's Orientale impact basin, evidence of its wilder days. Credit: NASA

 

Using data from NASA’s Gravity Recovery and Interior Laboratory (GRAIL) and Lunar Reconnaissance Orbiter (LRO) satellites and the Apollo Lunar Laser Ranging (LLR) project, Tuttle-Keane figured out the evolution of the moon’s spin by modeling lunar basins as they are today, then taking them back in time with numerical models that would show them as they were right after the intense asteroid encounters that formed them.

"The tumbling that happens right after basin formation can be quite extreme," Tuttle-Keane told Astronomy. “Sometimes the Moon completely unlocks from the Earth, or tumbles significantly.” He believes impact basins were born in bursts of light and rocky material that left gaping melted sores on the lunar surface.

This was next to all the volcanoes which were already erupting on the moon, their lava flow oozing into what would become the underground tunnels that are now being looked at as potential habitats for future moon dwellers.

The moon’s wild past eventually slowed down. Earth’s satellite became tidally locked with our planet again once tides got rid of the excess energy, and while the moon’s days of rocking and rolling finally ended hundreds of thousands of years later, this will probably change how you see that luminous dot in the night sky.

(via Astronomy Magazine)

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