AFP

PARIS- Europe next week will launch a trio of hi-tech satellites to explore something that may seem utterly mundane: Earth’s magnetic field. After all, magnetism has been with us for billions of years.

We harness it in innumerable ways, in navigation and electrical devices. What’s new?

Well, plenty, actually.

If all goes well, the 230-million-euro ($276-million) Swarm mission will explain some of the weird things happening to the planet’s magnetism.

And they are more than just curiosities.

“Earth’s magnetic field is a very important thing. It makes life possible on Earth by providing shelter against radiation from space,” said Albert Zaglauer, project manager at Astrium, which made the three satellites.

“The magnetic pole is changing, and the magnetic field is changing too. Why?”

Earth’s magnetism derives from superheated liquid iron and nickel, which swirl in the outer core about 3,000 kilometres (1,800 miles) beneath the surface.

Like a spinning dynamo, this subterranean metal ocean generates electrical currents and thus a magnetic field.

But contrary to what many may think, the field is not constant and immutable.

For one thing, the well-known gap between Earth’s magnetic north pole and its geographical north is growing.

Since 2001, the gap has been widening at the rate of 65 kilometres (40.6 miles) per year, compared with just 10 kilometres (six miles) per year in estimates in the early 1990s. In addition, the magnetic field has been weakening. Since the mid-19th century it has lost around 15 percent of its strength.

What’s going on?

Some experts wonder if this is a prelude to something really big: a reversal of magnetic polarity. Polarity switches occur around every 200,000 to 300,000 years, according to telltale magnetic signatures found in ancient sediments.

They are believed to occur when iron atoms in lava spewed by volcanoes adopt a polarity and retain it after the rock has solidified. Eventually a planetary tipping point is reached.

“Reversals are a slow process and do not happen with any regularity,” the European Space Agency (ESA) says.

“Nevertheless, the last time this happened was about 780,000 years ago, so we are now overdue for a reversal.”