AURORAL ORIGINS

How solar particles interact with our planet's magnetic field to create a dazzling light show

The origins of the aurora rest with our star. The Sun is always throwing out charged particles – mostly electrons and protons – in a moving plasma that we call the solar wind. On top of this, sometimes it releases more matter into the Solar System when the twisted magnetic field lines of the Sun break in a solar eruption or even a giant coronal mass ejection.

A coronal mass ejection is enormous! The Sun throws billions of tonnes of matter out into the Solar System, travelling at millions of kilometres an hour. We and all the other planets in the Solar System sit in this turbulent sea of plasma. This solar wind is constantly buffeting the Earth, sometimes weakly, sometimes strongly.

All these fast charged particles would be dangerous to life, but Earth has a magnetic field, that forms a protective shield called the magnetosphere. The solar wind interacts with Earth’s magnetic field, and if the magnetic field in the solar wind points southwards, the interaction is particularly strong; it sets up a cycle of changes in Earth’s magnetic field pattern.

This is called the Dungey Cycle and involves magnetic field lines being opened on the sunward side of the planet and closed again behind in a process called magnetic reconnection, where magnetic field lines snap and rejoin in a different configuration. This explosive process accelerates electrons into the Earth’s atmosphere on the night side of the planet, causing the aurora.

The aurora is the way our planet protects itself from the battering of the solar wind, absorbing the energy in its magnetic field and dissipating it in a beautiful light show.

Solar wind plasma Bow shock Magnetosheath Magnetopause Magnetosphere As the solar wind hits Earth’s magnetic field it is deflected around the outside, flowing in a layer called the magnetosheath. The cavity of the Earth in the solar wind is called the...