Earth’s Gravity Revealed in Unprecedented Detail
How the Earth would look like if its shape were distorted to make gravity the same everywhere on its surface. Areas of strongest gravity are in yellow and weakest in blue. Animation: European Space Agency
Excerpts from the European Space Agency and from Guardian UK, Ian Sample
After just two years in orbit, ESA’s GOCE satellite, A European spacecraft that skims the upper reaches of the atmosphere, has gathered enough data to map Earth’s gravity with unrivalled precision. Scientists now have access to the most accurate model of the ‘geoid’ ever produced to further our understanding of how Earth works.
The map shows how the pull of gravity varies minutely over the surface of the Earth, from deep ocean trenches to majestic mountain ranges.
The measurements have allowed scientists to create a computer model called a geoid that reveals what Earth would look like if its shape were altered to make gravity equal at every point on the surface.
The new geoid was unveiled today at the Fourth International GOCE User Workshop hosted at the Technische Universität München in Munich, Germany. Media representatives and scientists from around the world have been treated to the best view yet of global gravity. The map shows areas of strongest gravity in yellow and weakest in blue.
The geoid is the surface of a global ocean in the absence of tides and currents, shaped only by gravity. It is a crucial reference for measuring ocean circulation, sea-level change and ice dynamics, all affected by climate change.
Data from the five-metre-long spacecraft will be crucial for understanding sea level changes, shifts in ice flows and how ocean currents, which are driven by gravity, respond as the planet warms over the next few decades.
The spacecraft circles the Earth at an altitude of 150 miles (250km) and uses an ion rocket to prevent it losing height as it flies through wisps of atmosphere.
Described by project manager Andrea Allasio as “the Ferrari of space probes”, Goce maps Earth’s gravitational field by recording its exact position with GPS and detecting variations in the pull of gravity accurate to one part in ten million million.
“They show that GOCE will give us dynamic topography and circulation patterns of the oceans with unprecedented quality and resolution. I am confident that these results will help improve our understanding of the dynamics of world oceans.”
Earth’s gravity is subtly influenced by all manner of changes in the structure and topography of the Earth. The planet is not a perfect sphere, instead bulging around the equator, making gravity weaker there than at the poles. Gas fields, mineral deposits, aquifers and rock formations also affect the pull of gravity.
Information from Goce is already being analysed to get a deeper understanding of the geological processes that cause earthquakes.
The recent quake that brought devastation to Japan was triggered by the sudden movement of tectonic plates beneath the ocean. Since this earthquake was caused by tectonic plate movement under the ocean, the motion cannot be observed directly from space. However, these dramatic movements in rock (earthquakes) leave signatures in gravity data, which could be used to understand the processes leading to these natural disasters and ultimately help to predict them.
The GOCE satellite was launched in March 2009 and has now collected more than 12-months of gravity data. The probe has enough fuel to fly until the end of 2012, a doubling of its intended mission life.
“At its early conception, Goce was more like science fiction. Goce has now clearly demonstrated that it is a state-of-the-art mission,” said Volker Liebig, director of Esa’s Earth Observation Programmes.