Earth Wobbles On Its Axis

Paul Gonzalez
• Saturday, 27 November, 2021
• 7 min read

Using satellite data on how water moves around Earth, NASA scientists have solved two mysteries about wobbles in the planet's rotation -- one new and one more than a century old. Although a desktop globe always spins smoothly around the axis running through its north and south poles, a real planet wobbles.

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(Source: www.slideshare.net)


Earth's spin axis drifts slowly around the poles; the farthest away it has wobbled since observations began is 37 feet (12 meters). These wobbles don't affect our daily life, but they must be taken into account to get accurate results from GPS, Earth -observing satellites and observatories on the ground.

In a paper published today in Science Advances, Narendra Adhara and Erik Ivies of NASA's Jet Propulsion Laboratory, Pasadena, California, researched how the movement of water around the world contributes to Earth's rotational wobbles. Earlier studies have pinpointed many connections between processes on Earth's surface or interior and our planet's wandering ways.

Scientists have suggested that the loss of mass from Greenland and Antarctica's rapidly melting ice sheet could be causing the eastward shift of the spin axis. The GPL scientists assessed this idea using observations from the NASA/German Aerospace Center Gravity Recovery and Climate Experiment (GRACE) satellites, which provide a monthly record of changes in mass around Earth.

Adhara and Ivies' calculations showed that the changes in Greenland alone do not generate the gigantic amount of energy needed to pull the spin axis as far as it has shifted. In the Southern Hemisphere, ice mass loss from West Antarctica is pulling, and ice mass gain in East Antarctica is pushing, Earth's spin axis in the same direction that Greenland is pulling it from the north, but the combined effect is still not enough to explain the speedup and new direction.

This region has lost water mass due to depletion of aquifers and drought, but the loss is nowhere near as great as the change in the ice sheets. “Despite tremendous theoretical and modeling efforts, no plausible mechanism has been put forward that could explain this enigmatic oscillation,” Adhara said.

pesla wobble earth axis its spin wobbles
(Source: www.slideshare.net)

“Our study shows that this legacy data set can be used to leverage vital information about changes in continental water storage and ice sheets over time.” NASA uses the vantage point of space to increase our understanding of our home planet, improve lives and safeguard our future.

NASA develops new ways to observe and study Earth's interconnected natural systems with long-term data records. The agency freely shares this unique knowledge and works with institutions around the world to gain new insights into how our planet is changing.

Since the 1990s, space-based measurements have also confirmed that the Earth's axis of rotation drifts by a few centimeters a year, generally toward Hudson Bay in northeastern Canada. Researchers knew that a proportion of this wobble was caused by glacial prostatic adjustment, an ongoing process since the end of the last ice age 16,000 years ago.

(Image credit: NASA/ JPL-Caltech)But in the new research, published in the November issue of the journal Earth and Planetary Science Letters, Adhara and his colleagues found that glacial prostatic adjustment was only responsible for about 1.3 inches (3.5 centimeters) of axis wobble per year. To fill in the gap, the research team built a computer model of the physics of Earth's spin, feeding in data about changes in the balance of land-based ice and ocean waters over the 20th century.

The researchers also accounted for other shifts in land and water, such as groundwater depletion and the building of artificial reservoirs, all part of humanity's terraforming of the planet. That's because Greenland has released a large amount of water that was once locked up on land into the oceans, where its mass has been redistributed, Ivies told Live Science.

axis polar nasa earth drift why motion reasons earths line spin drifting explained three called its ice greenland yellow
(Source: www.ibtimes.co.in)

Mountain glaciers and small ice caps elsewhere have also contributed to sea-level rise, he said; but they aren't as concentrated, and their effects on the Earth's rotation often cancel each other out. By including convection in the model of Earth's wobble, the researchers had accounted for the last third of the changes in the spin over the 20th century.

For example, Adhara said, Greenland's melt has become an increasingly large contributor to changing the axis location in the past 15 years, which is pushing the drift eastward. When it rotates on its spin axis -- an imaginary line that passes through the North and South Poles -- it drifts and wobbles.

Using observational and model-based data spanning the entire 20th century, NASA scientists have for the first time identified three broadly-categorized processes responsible for this drift -- contemporary mass loss primarily in Greenland, glacial rebound, and mantle convection. “The traditional explanation is that one process, glacial rebound, is responsible for this motion of Earth's spin axis.

But recently, many researchers have speculated that other processes could have potentially large effects on it as well,” said first author Narendra Adhara of NASA's Jet Propulsion Laboratory in Pasadena, California. “We assembled models for a suite of processes that are thought to be important for driving the motion of the spin axis.

In general, the redistribution of mass on and within Earth -- like changes to land, ice sheets, oceans and mantle flow -- affects the planet's rotation. In fact, a total of about 7,500 gigatons -- the weight of more than 20 million Empire State Buildings -- of Greenland's ice melted into the ocean during this time period.

moon earth magnetic field play role sun effects gravitational maintaining thought major mantle core rotation earths cause iron outer axis
(Source: astronomynow.com)

This makes Greenland one of the top contributors of mass being transferred to the oceans, causing sea level to rise and, consequently, a drift in Earth's spin axis. While ice melt is occurring in other places (like Antarctica), Greenland's location makes it a more significant contributor to polar motion.

You may not be aware that the earth also wobbles slightly, causing the orientation of the axis to shift by a few inches per year. Over the course of the 20th century, scientists watched in fascination as the Earth’s axis swung back and forth by as much as several meters.

NASA used observational and model-based data from past decades to determine once and for all what factors affect the planet’s wobble. It landed on three main causes: loss of ice mass, glacial rebound, and mantle convection.

The observed direction of polar motion, shown as a light blue line, compared with the sum (pink line) of the influence of Greenland ice loss (blue), postglacial rebound (yellow) and deep mantle convection (red). Glacial rebound is related to the loss of ice, but the mechanism by which it affects Earth’s wobble is different.

That ground slowly rises back up to its natural level, and that changes the distribution of mass and affects the wobble. With the causes identified, scientists can track polar motion and understand which changes are due to human activity and which are a consequence of the nature of Earth.

pole north ysengrimus nord moving change climate landscape earth mirror way axis
(Source: www.mirror.co.uk)

In astronomy, an axis refers to the imaginary line that an object, usually a planet, rotates around. Earth's rotational axis is an imaginary straight line that runs through the North and South Pole.

In our illustrations, Earth's axis is drawn as a straight red line. Earth's obliquity angle is measured from the imaginary line that runs perpendicular to another imaginary line; Earth's ecliptic plane or orbital plane (see illustration).

Axial precession can be described as a slow gyration of Earth's axis about another line intersecting it. It outlines the shape of a pair of cones or two spinning tops connected at the tips, which would be at the center of Earth.

Greek astronomer Hipparchus of Nice is historically credited as the man who first proposed that Earths axis gradually shifts, though very slowly. Hipparchus made his discovery around 130 BCE, based on comparisons of astronomical observations more than a century apart.

Because Earth orbits the Sun at an angle, the solar energy reaching different parts of our planet is not constant, but varies during the course of a year. At the same time, the Southern Hemisphere tilts away from the Sun, resulting in shorter days.

earth wobble nasa change different planet causing scientists water north around rain figured 2000 space move pole climate ice resources
(Source: cnbc.com)

Several studies have suggested global warming has contributed to an increase in ice melt in Greenland, Antarctica and other parts of the world. Another factor noted by researchers is glacial rebound, a process where land once depressed by heavy glaciers begins to rise.

“The traditional explanation is that one process, glacial rebound, is responsible for this motion of Earth's spin axis, ” said Adhara. Scientists have long known that the axis on which the planet spins is prone to wavering, but some reasons have escaped understanding.

But researchers at NASA's Jet Propulsion Laboratory say droughts and heavy periods of rain in different places around the planet are causing Earth to shake in space. The movements of the Earth's axis are crucial to understand, since they affect the performance of satellites and global positioning systems.

The team published its findings Friday in the peer-reviewed open access journal Science Advances. Scientists have thought the melting and forming of ice sheets around the world changed the distribution of mass around the planet enough to shift the polar axis.

The Greenland and Antarctic ice sheets are responsible for most of the force pulling and pushing the polar axis. But Adhara and Erik Ivies, both researchers at NASA's Jet Propulsion Laboratory, charted the maximum impact these kinds of changes could have on the movement of the axis and determined there had to be some other force at work.

earth axis its universe does spin rotation times many year today
(Source: www.revimage.org)

Examining images from the GRACE satellite, Adhara and Ivies found that changes in the amount of water on land corresponds to the shifts in the axis.

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