Australian continent shifts and tilts back and forth by several millimeters each year because of changes to the Earth’s center of mass, according to a new study.
The findings could help scientists better track the precise location of Earth’s center of mass, which is important for GPS and other satellite measurements, according to the study’s author.
All bodies have a center of mass, or the average position of the mass of an object. Earth’s center of mass lies roughly at the center of the planet’s molten core, about 6,000 kilometers (about 3,700 miles) beneath the surface.
Seasonal changes to the distribution of water on Earth’s surface–largely through precipitation and evaporation–shift the planet’s center of mass a few millimeters in different directions.
The new study finds these movements cause Earth’s smallest continent to move back and forth with the seasons.
Australia moves northwest by about 1 millimeter during its summer (winter in the Northern Hemisphere).
At the same time, its northwestern edge tilts downwards by 2 to 3 millimeters, while the southeastern edge is lifted up by 2 to 3 millimeters.
During its winter (summer in the Northern Hemisphere), the trend reverses, and the continent shifts southeast and reverses its tilt.
These changes are not enough to be felt by the country’s inhabitants but are enough to be detected by satellites.
To track Australia’s motion, the researchers measured changes in the locations of 14 land-based GPS stations across the continent.
Although their orbit is about 20,000 kilometers (12,500 miles) above Earth’s surface, GPS satellites can detect changes to land-based stations that are smaller than a millimeter.
The researchers then used data from the Gravity Recovery and Climate Experiment (GRACE), which uses two satellites to measure changes in the strength of gravitational pull over Earth, to measure the location of water.
While the result may not amount to much of a difference on a day-to-day basis, it could be a concern for precision measurements, like those taken to determine sea level.
Citation: Han SC. (2016). Seasonal clockwise gyration and tilt of the Australian continent chasing the center of mass of the Earth’s system from GPS and GRACE. Journal of Geophysical Research, published online. DOI: 10.1002/2016JB013388.
Figure legend: This Knowridge.com image is credited to Hans Braxmeier.