South Atlantic Anomaly
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Anomaly in Earth's magnetic field

Nasa scientist Dr Jack Connerney has been studying the growth of a weak patch in Earth's magnetic field, known as the South Atlantic Anomaly, thought to be linked to flow patterns in the planet's molten outer-core.

The magnetic field falls to below 30 microteslas (0.3 gauss), half the strength of that toward the poles, resulting in problems for satellites passing over the region.

Horizon: The Core is on BBC Two at 21:00 BST on Wednesday 31 August. Watch more clips or catch up afterwards via iPlayer.

  • 31 Aug 2011