The Sun's magnetic field and solar wind - mainly in the form of electrons and protons coming out of the Sun - protects the entire Solar System by acting as a sort of shield from cosmic rays (very energetic particles and radiation from outer space).

BBC: Viewpoint: The Sun and climate change

The most persuasive evidence that Voyager 1 has crossed the termination shock is its measurement of a sudden increase in the strength of the magnetic field carried by the solar wind, combined with an inferred decrease in its speed.

BBC: Voyager impression (Nasa)

They will focus on the places above the poles where the wind pierces the earth's magnetic defences and causes, among other things, the shimmering lights of the aurora borealis and aurora australis, and interference with radio communications.

ECONOMIST: Birds of a feather

But since the wind consists of charged particles, it will interact with a magnetic field.

ECONOMIST: Rockets are not the only way to travel through outer space

These craft will study the interaction between the solar wind (the breeze of electrically charged particles emitted by the sun) and the earth's magnetic field.

ECONOMIST: Birds of a feather