The above image shows the “vertical gravity gradient change” based on data from two Earth-monitoring satellites. The redder areas experienced the greatest gravity shifts, but the overall change in gravitational force was very slight. Credit ESA, DGFI/Planetary Visions
Although not designed to map changes in Earth’s gravity over time, ESA’s extraordinary satellite has shown that the ice lost from West Antarctica over the last few years has left its signature.
More than doubling its planned life in orbit, GOCE spent four years measuring Earth’s gravity in unprecedented detail.
Scientists are now armed with the most accurate gravity model ever produced. This is leading to a much better understanding of many facets of our planet – from the boundary between Earth’s crust and upper mantle to the density of the upper atmosphere.
The strength of gravity at Earth’s surface varies subtly from place to place owing to factors such as the planet’s rotation and the position of mountains and ocean trenches.
Changes in the mass of large ice sheets can also cause small local variations in gravity.
Recently, the high-resolution measurements from GOCE over Antarctica between November 2009 and June 2012 have been analysed by scientists from the German Geodetic Research Institute, Delft University of Technology in the Netherlands, the Jet Propulsion Lab in USA and the Technical University of Munich in Germany.
Remarkably, they found that the decrease in the mass of ice during this period was mirrored in GOCE’s measurements, even though the mission was not designed to detect changes over time.
Using gravity data to assess changes in ice mass is not new. The NASA–German Grace satellite, which was designed to measure change, has been providing this information for over 10 years.
However, measurements from Grace are much coarser than those of GOCE, so they cannot be used to look at features such as Antarctica’s smaller ‘catchment basins’.
Using 200 million measurements collected by ESA’s CryoSat mission between January 2011 and January 2014, researchers from the Alfred Wegener Institute in Germany have discovered that the Antarctic ice sheet is shrinking in volume by 125 cubic kilometres a year. The study, which was published in a paper published on 20 August 2014 in the European Geosciences Union’s Cryosphere journal, also showed that Greenland is losing about 375 cubic kilometres a year. Read full article.
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