The Length of a Day Oscillates Every 6 Years, And We May Finally Know Why

How we think about our planet’s center may need to be seriously updated.

New evidence suggests that, instead of consistently rotating faster than Earth’s spin, the solid inner core oscillates – spinning first in one direction with respect to the surface far above, then the other, changing direction every six years.

This not only has implications for our understanding of the inner workings of our home world, it can also neatly explain a mystery that has perplexed scientists for some time: an oscillating variation in the length of Earth’s day, with a period of 5.8 years.

“From our findings, we can see the Earth’s surface shifts compared to its inner core, as people have asserted for 20 years,” said geophysicist John E. Vidale of the University of Southern California, Los Angeles (UCLA).

“However, our latest observations show that the inner core spun slightly slower from 1969-71 and then moved the other direction from 1971-74. We also note that the length of a day grew and shrank as would be predicted. The coincidence of those two observations makes oscillation the likely interpretation.”

Although our understanding of Earth’s core has developed a lot in recent decades, there’s still a lot we don’t know. We can’t just go there and take a gander at it; everything we know, we’ve gleaned from indirect observations, such as seismic waves propagating and bouncing through the entire planet.

But this is still a very effective tool. Scientists have been able to ascertain that Earth’s inner core is probably a hot, dense ball of solid iron, measuring roughly 2,440 kilometers (1,516 miles) across, a little bigger than the size of Pluto. Evidence also suggests that it demonstrates superrotation, rotating faster than Earth itself.  …