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An Aging Satellite Just Revealed the Exotic Structure of Earth's Interior

Gravity doesn't lie.

The European Space Agency's GOCE mission came to a close more than seven years ago, but scientists are still uncovering substantial finds from the retired satellite's gravity data — which allows us to dive deep into the Earth's interior and learn what makes it tick.

Scientists have combined GOCE data with surface-based measurements to create a novel model of the Earth's crust and upper mantle, according to a recent study published in the Geophysical Journal International.

This marks the first time a model of the Earth's interior was created this way — and it's unearthing (pun intended) new processes of plate tectonics — a feature of our planet that causes volcanic eruptions and earthquakes.

Space-based gravity data enhances our picture of Earth's interior structure

Crucial to the science of plate tectonics is a firm grasp of the Earth's lithosphere — which consists of the planet's rocky outer crust, in addition to the semi-melted molten top layers of the planet's upper mantle.

Plate tectonics describe how the Earth's crust is divided into a patchwork of plates sliding in slow, monumental motion over the shifting top of the upper mantle. As this happens, it forms new seafloor along mid-ocean ridges, volcanoes go critical and erupt, mountains rise, and earthquakes happen. Enhancing our scientific grasp of these processes depends on advancing knowledge of differences in the lithosphere's chemical composition and varying temperature.

Conventionally, geophysicists measure the speed of seismic wave propagation once an earthquake begins to predict and study the distribution of physical properties under the Earth's surface. The speed of seismic waves' motion through the planet is mainly determined by the temperature of subsurface rocks — and density, but less so.

Gravity data from space greatly enhances this picture — because the effect of gravity is directly tied to the density of different parts of the Earth. Data from orbiting satellites can offer uniform accuracy and coverage across the planet — especially where ground measurements rarely, if ever, happen.

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Earth's lithosphere is different under different oceans

The new research shows how scientists built a new model of the lithosphere by combining seismological data gathered via petrological data and seismological observations (on foot). The former comes from studying rocks that were brought to the planet's surface — in addition to laboratories where extreme pressures and instant-death temperatures of Earth's interior are recreated for scientific investigation.

"Earlier global models of the crust or lithosphere suffered from limited resolution or were based on a single method or dataset," said co-author of the paper Javier Fullea, who is also from Complutense University of Madrid and the Institute for Advanced Studies, according to a report from Phys.org. "Only recently available models were able to combine multiple geophysical data, but they were often only on regional scales or they were limited by how the different data are integrated."

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"For the first time, we've been able to create a new model that combines global-scale multiple terrestrial and GOCE satellite datasets in a joint inversion that describes the actual temperature and composition of mantle rocks," added Fullea.

The new model from GOCE showed for the first time how different the sub-lithospheric mantle is under different oceans — while also revealing more about how fast mid-oceanic ridges spread, suggesting that their speed and morphology could be related to deep thermal and chemical structure. With this knowledge, we may one day make more accurate long-term predictions about seismic activity, as our living world evolves.

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