This is your Earth on gravity

This lumpy blob is a gravity map of our planet, showing an exaggerated view of where sea level would be if it weren't for waves, tides, currents, or weather. The European Space Agency's GOCE satellite has created the most detailed planetary gravity map ever, and it could help us understand everything from climate change to earthquakes.

To get all technical on you, this image is showing what's called the geoid. If you imagine the Earth's surface totally smoothed out, you'd get a nice round reference ellipsoid of our planet. And if you then take that reference ellipsoid and squish it around to account for differences in gravity caused by land masses and mountains and denser regions of rock and such, you get the geoid.

Really, the easiest way to think about it is just in terms of sea level: in the same way that the moon's gravity changes sea level through tides, the Earth's gravity changes sea level too, and the geoid simply shows where sea level would be all over the globe if it weren't for waves and stuff. The globe in the pic (and the video below) is a little bit exaggerated; in reality, the geoid only deviates in elevation by a couple hundred meters.

The reason we care about the geoid is that it's hard to measure things like ocean dynamics without having an accurate reference point to start from. Also, earthquakes leave signatures in the geoid, and with enough gravity data, it may be possible to predict where they're likely to happen next.


The spacecraft doing all this work is GOCE, which somehow stands for "Gravity Field and Steady-State Ocean Circulation Explorer." GOCE is equipped with six extremely sensitive accelerometers for measuring gravity in three dimensions. It's also got an ion engine on it to compensate for the tiny bits of atmosphere that it has to plow through, and it's scheduled to keep updating its gravity map through 2012.

ESA GOCE, via The Age

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