Earth's inner core may have started spinning other way | Hacker News Reader

Earth's inner core may have started spinning other way

phys.org

4 pointssamizdis3 comments

I don't know enough about the physics of spinning bodies; how could a sphere slow down and change direction periodically? Shouldn't it keep spinning in the same direction as the rest of the planet?

For a phys.org article it's pretty bad.

The key part is smothered:

    The study's authors, Xiaodong Song and Yi Yang of China's Peking University, said they found that the inner core's rotation "came to near halt around 2009 and then turned in an opposite direction".

    "We believe the inner core rotates, relative to the Earth's surface, back and forth, like a swing," they told AFP.

"relative to the Earth's surface" does the heavy lifting - think of two spheres rotating together with a sticky fluid layer between them.

Now think of the inner sphere speeding up, then slowing down (relative to the outer) - they're rotaing together but have a coupled "sprung" oscillation.

Standing on a fixed point on the earths surface looking straight down you would "see" the corresponding point on the inner core moving ahed of you and then after a while moving back "in reverse".

For anyone interested in a detailed "State of Inner Core Knowledge" from 2015 .. which is still current as the same questions are still more or less open, there are just seven years more papers arguing this Vs that; see:

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/201...

That's a wonderfully simple explanation. Thanks!

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