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Did Earth once spin sideways?

A Mars-sized space object likely knocked Earth on its side 4.4 billion years ago, and knowledge of this is disrupting 50 years of work calculating the moon’s historic orbit. The event—not-so-scientifically referred to as the “big whack”—left Earth spinning rapidly at a rate of less than 5 hours per rotation on a dramatically tilted axis, Astronomy Now reports. At that time, the newly formed moon would have been orbiting around Earth’s equator, not on the ecliptic plane seen today. Scientists now believe that under those circumstances, in order for the moon to reach its current position, it probably moved in a dizzyingly abrupt zigzag pattern, according to a recent study published in Nature. All the while the moon’s internal tides were in a tug-o-war with Earth’s that resulted in a stalemate lasting millions of years, which, in turn, slowed Earth’s rotation and realigned both its own and the moon’s tilt.

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