The Weight of The World

Satelites Map Earth's Gravity To Plot Climate Change And Ocean Currents!


As a falling apple demonstrated to Newton, objects with mass exert a gravitational force. But while the Earth exerts pretty much the same pull on any object, it's not exactly the same the world over. Precisely how gravity varies has now been reveal by a map obtained from data collected by a pair of orbiting satelites.

The satelites jointly operated by NASA and German Aerospace Center, make up the Gravity Recovery and Climate Experiment (GRACE). The map shows that a bigger pull is produced by mountain ranges and the mid-Atlantic ridge, where new crust is created underwater. Thats as it should be. Those regions have a greater concentration of mass and they therefore exert a slightly bigger gravitational force, shown by the red region on the map. The blue regions depict areas with lower gravity than they would have if the Earth was perfectly smooth.

But GRACE is sensitive enough to pick up far more minute variations. These come from ocean currents, which cause water to build up in some places more than in others, concentrate mass and exert a slightly bigger pull as a result. Shifting polar ice caps and seasonal changes in groundwater are also responsible for moving mass. And because these masses are constantly shifting, it means that Earth's gravitational field is constantly changing too. That's why GRACE will produce a new map every month.

By studying how gravity has changed, scientists will get a better picture of how winds, currents and tides affect circulation in the oceans. GRACE brings the true state of the oceans into much sharper focus, so we can better see ocean phenomena that have a strong impact on atmospheric weather patterns, fisheries and global climate change, says Dr Byron Tapley, who works on the project at the University of Texas.

The way GRACE can record gravity in such detail is almost as amazing as the map itself. The two satelites fly over the Earth on parallel ordits 220km apart. Mass acting on them changes their separation - differences as small as one tenth the width of a human hair can be detected.

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For a closer look at this project, and some great graphic click the link below

www.csr.utexas.edu...

(this was taken from an article in the Focus magazine, this months)




[Edited on 21-9-2003 by blackwidow666]