Why is Earth’s spin axis drifting?

earthsky.org | 9/23/2018 | Deborah Byrd
Click For Photo: http://en.es-static.us/upl/2018/09/earth-spin-polar-motion-300x169.jpg

The light blue line shows the observed direction of “polar motion” – the drift of Earth’s spin axis. The pink line represents the sum of the influence of Greenland ice loss (blue), postglacial rebound (yellow) and the highly uncertain contribution of deep mantle convection (red). These lines represent the direction of drift, not the amount. Over the 20th century, the amount of drift was 11 yards (10 meters). Image via NASA/ JPL-Caltech.

Unlike a plastic globe of Earth, the real planet Earth isn’t perfectly round and doesn’t spin smoothly. The imaginary line around which Earth spins – passing through the North and South Poles – is called its spin axis. Scientists have known for a long time that Earth’s spin axis drifts and wobbles. Measurements over the 20th century show that Earth’s spin axis drifts by about 4 inches (10 cm) per year. Over the course of a century, that’s more than 11 yards (10 meters). This week (September 19, 2018), NASA scientists announced they’ve used observational and model-based data spanning the 20th century in order to identify – for the first time – three processes primarily responsible for this drift.

Processes - Loss - Ice - Greenland - Lifting

The three processes are mass loss due to melting ice (mostly in Greenland), the lifting of land masses as glaciers have melted since the last ice age (aka glacial rebound), and the slow creeping motion of rocky material in Earth’s interior mantle, caused by convection currents carrying heat from our planet’s interior to its surface (this third process is called mantle convection).

Scientists call the drift of Earth’s spin-axis its polar motion. Surendra Adhikari of NASA’s Jet Propulsion Laboratory in Pasadena, California is first author on the new paper describing the causes for the drift. He said:

Explanation - Process - Rebound - Motion - Earth

The traditional explanation is that one process, glacial rebound, is responsible for this motion of Earth’s...
(Excerpt) Read more at: earthsky.org
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