Will the Earth ever stop spinning?

The probability for such an event is practically zero in the next few billion years. But suppose something like this could happen? The outcome depends on just how suddenly it stopped. If the Earth stopped spinning very quickly, say within a day, the atmosphere would still be in motion with the Earth's original 1100 mile per hour rotation speed at the equator. All of the landmasses would be scoured clean of anything not attached to bedrock. If the process happened gradually over billions of years, the situation would be very different, and it is this possibility that is the most likely as the constant torquing of the Sun and Moon upon the Earth finally reaches it's conclusion. As for other effects, presumably the magnetic field of the Earth is generated by a dynamo effect that involves its rotation. If the Earth stopped rotating, its magnetic field would no longer be regenerated. It would decay to some low, residual value due to the very small component that is 'fossilized' in its crustal rocks. There would be no more 'northern lights' and the Van Allen radiation belts would probably vanish, as would our protection from cosmic rays and other high-energy particles. This is a significant biohazard for astronauts, but not for those of us living on the ground.

Will its spin ever change in the future through natural causes? We don't know. The only way we think it could change in any radical way is by a major impact with another celestial body. Even the biggest asteroid we know, Ceres (636 miles in diameter), is not really big enough to do much more than annihilate all life on this planet. It might tilt the Earth's axis by a few degrees depending on the details of the collision. But much of the kinetic energy of the impact would be used in blasting a portion of the outer atmosphere into space along with billions of tons of crustal rock. There are no foreseeable asteroid collisions with Earth big enough to be important in triggering more that some surface damage for the foreseeable future. What we can't completely rule out are changes in the way that mass is distributed on the crust. If you move the continents around, some geologists think you could make Earth act like a tippy-top. They even think this may already have happened. It's called the Snowball Earth model.

This answer was updated in 2011. See my books: The Astronomy Cafe (1998) and Back to the Astronomy Cafe (2003) for more FAQs in printed form. Author: Dr. Sten Odenwald, Copyright 2011

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