A sleek satellite orbiting Earth has confirmed that the planet is not the simple squashed sphere we often imagine it to be. It is, in fact, more like a lumpy potato.
Nearly a year's worth of gravitational measurements from the European Space Agency's Gravity Field and Steady-State Ocean Circulation Explorer (GOCE) have yielded a colourful map portraying the geoid – the shape the Earth's surface would be if it was entirely covered by water and influenced by gravity alone.
The result is not a smooth sphere because mass is not distributed evenly within the Earth's mantle. Different parts of the globe exert a different gravitational pull on the ocean, meaning that sea level is lower than expected in some places – represented by blue patches – and higher than expected in others – the red and yellow areas.
In the visualisation, the vertical scale has been exaggerated by a factor of 7000, so the pits and crests are 7000 times shallower or taller, respectively, than depicted here.
The visualisation shows true sea level, liberated from the artefacts of tides and winds. Mission scientist Roger Haagmans explains the influence of winds on the oceans through a simple model: suppose you have a bathtub full of water and you place a fan on one side to blow the surface: the water will pile up on the opposite side. Now shut the fan off, and the water will settle at a new level, according to gravity. Read More
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