090310 Mapping the Earth’s gravity as never before

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Mapping the Earth’s gravity as never before

BY DR EMILY BALDWIN

ASTRONOMY NOW

Posted: 10 March, 2009

The most sophisticated Earth observation satellite will launch next week to map our planet’s gravitational field with unprecedented resolution and accuracy.

Gravity data is essential for monitoring ocean circulation and sea-level change, as well as processes linked to volcanic and earthquake activity. GOCE - the Gravity field and steady-state Ocean Circulation Explorer - is the first of a series of Earth Explorer satellites to enable cutting edge research regarding the Earth’s atmosphere, biosphere, hydrosphere, cryosphere and interior.

GOCE is a unique five-metre long satellite that will map the Earth's gravity in greater detail than ever. Image: ESA-AOES Medialab.

The one-tonne satellite carries a highly sensitive gradiometer that will allow scientists to plot tiny variations in the Earth’s gravity field in three dimensions. This will result in the most detailed high-resolution map of the geoid, the reference (so-called “ground-zero”) level of the planet, as well as highlighting gravitational anomalies. Mapping a planet in this way provides insight into its internal structure, as well as vital reference data for ocean circulation and climate studies. The mission will also have practical applications in construction, planning and surveying.

The science requirements of the mission mean that the spacecraft has to orbit the Earth at close enough quarters to gather high-accuracy gravitational data while being able to filter out disturbances caused by the remaining traces of the atmosphere in low Earth orbit, at an altitude of just 260 kilometres. The result is the five metre long aerodynamic satellite equipped with low power ion thrusters to compensate for atmospheric drag. Unlike other satellites, it has none of the usual moving parts that could interfere with the gravity measurements. GOCE, with its sensor, system of supporting instrumentation and control elements, actually forms a single composite gravity-measuring device.

GOCE is scheduled to launch on 16 March from the Plesetsk Cosmodrome in Northern Russia. Later in the year, two other Earth Explorer missions will launch to study soil moisture and ocean salinity, and ice sheet thickness, respectively. Additional Earth Explorer missions are also being designed to address other aspects of the Earth environment, from the evolution of the magnetic field to the Earth’s radiative balance.

A live televised transmission of the launch of GOCE will be streamed online at http://www.esa.int/goce.