Gravity Map Gets to Grips with Planet’s Pull

[WASHINGTON] The most accurate map yet of Earth’s gravitational field has been released – the first result of the Gravity Recovery and Climate Experiment (GRACE), run jointly by NASA and the DLR, Germany’s aerospace research centre. Oceanographers hope to use the map to model deep oceanic currents and heat fluxes, and so better understand their effects on global climate.

“It’s an order of magnitude better than anything that’s gone before,” says Byron Tapley, the project’s principal investigator and director of the Center for Space Research (CSR) at the University of Texas at Austin. The map, called GRACE Gravity Model 01, was based on a preliminary analysis of 111 days of mission data. It was published on the CSR website on 21 July, a few months ahead of the main phase of the mission.

The GRACE mission comprises two identical satellites, one 220 kilometres ahead of the other. The lead satellite encounters local variations in the gravity field first, and so temporarily pulls away from its partner (see Nature 416, 10-11; 2002). The map was created by following these minute changes in separation, which are measured to the nearest micrometre by onboard sensors.

Use the force: the raised, red areas in GRACE’s gravity map show where Earth’s pull is strongest.

This may explain why Atlantis sank.