Because Jupiter's axis of rotation does not quite line up with its magnetic axis, the moons that orbit the planet feel such a fluctuating magnetic force.

ECONOMIST: Blue moon

Beatriz Nofal, of Eco-Axis, a Buenos Aires business consultancy, points out that all the Mercosur countries, especially Brazil, have used such devices as tax credits on capital-goods imports, which break the principle of a customs union.

ECONOMIST: Mercosur’s malaise | The