Space shields may sound like they belong on Star Trek, but there's one protecting you right now: the Earth’s magnetic field.
Our planet is under continual assault from the Sun, which sends streams of electrically charged particles hurtling through space at speeds of up to 750 km/s. Known as the solar wind, these particles can ionise atoms and harm cells, potentially inflicting some serious damage. But don’t panic! Most of these particles are deflected by the Earth's magnetic field before they even reach our atmosphere, which itself mops up most of the stragglers.
The Earth produces a vast magnetic field stretching out into space, just like the field that would result from a gigantic bar magnet placed in the planet's centre. Buffeted by solar wind, this magnetic field is distorted into a tear-drop shape and is called the magnetosphere.
Magnetic fields are of course invisible, but physicists are able to build up a picture of the magnetosphere and monitor its natural variations over time using specialised instruments on board satellites.
They are also on the lookout for clues suggesting that the Earth's poles might soon flip – a phenomenon which has occurred regularly throughout the planet's history.
We'd be lost without the magnetosphere in more than one sense: not only would adventurers' compass needles no longer point North, but we, along with the rest of life on Earth, would be unlikely to survive. Even with the magnetosphere's protection, periods of exceptionally high solar activity have been known to disrupt power grids, satellites and GPS navigation.