They used a beam of photons to measure the small magnetic field produced by a gas made up of a million ultra-cold rubidium atoms.

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"While our results are still very new, our thinking is that the mercury detected by Lamp from the Grail site might be related to an enhancement at the poles caused by mercury atoms generally hopping across the surface and eventually migrating toward the cold polar regions, " said Kurt Retherford, the chief scientist for Lamp.

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