Map Earth's Fourth Dimension

Map Earth's Fourth Dimension

A gravitational rainbow points to our planet's invisible topography.
by Bjorn Carey

From the August 2006 issue; published online August 14, 2006




Your weight is not the same everywhere. Because Earth is not a perfect sphere, the pull of gravity is stronger in some places than in others. It's also in a constant state of change, moving with Earth's mantle, falling sea levels, and even tropical storms. The Gravity Recovery and Climate Experiment mission, better known as GRACE, was launched in 2002 by NASA and the German Aerospace Center to measure exactly how what goes up must come down.

1 AMAZING GRACE
Before GRACE, scientists had only a vague idea of what Earth's gravity map might look like. But even the tiniest rises and dips in Earth's gravity push GRACE's two identical satellites together or pull them apart, generating a map so precise it can chart monthly changes in Earth's crust and seasonal ocean currents.

2 BIG BEER BELLY
Earth's rotation causes our planet to bulge at the equator. This extra girth around the middle partly explains why things weigh more at the poles.
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3 RAPID WEIGHT LOSS
Once the central bulge is accounted for, more subtle gravity differences appear. For example, what goes up falls a tad faster in London than it does in Athens.

4 ULTIMATE YO-YO DIET
Earth's mantle has mountain-valley systems resulting from old tectonic clashes, which make gravity's pull strongest in the southwestern Pacific and weakest just off the southern tip of India. So the fastest way to lose weight is a direct flight from Singapore to Sri Lanka.

5 BUILT LIKE AN AMAZON
Annual flooding increases (reddish areas) and decreases (bluish areas) the gravity of the Amazon basin. Because GRACE is sensitive enough to measure rainfall, it helps scientists understand how climate changes affect the rainy season.

6 THE BIGGEST LOSER
From 2002 to 2005, GRACE found that Antarctica's ice mass had decreased by 36 cubic miles a year, helping prove that global warming and melting polar ice play a role in rising sea levels.

SOURCE: http://discovermagazine.com/2006/aug/map4d