What is an aurora?

They’re not just on Earth, you know. Read on to find out how auroras form on different planets in the Solar System.


Earth aurora

The Sun is constantly giving out energy in the form of charged particles that make their way throughout the Solar System unheeded by the vacuum of space. However, around most of its eight major planets is a magnetosphere caused by activity in that planet’s core, namely the induction of currents. When these charged particles from the Sun come into contact with the magnetosphere of a planet, the results are nothing short of remarkable.

A planet’s magnetosphere extends in a circle from pole to pole, with the pressure of the solar wind also extending its tail far beyond the planet. When the particles from the Sun come into contact with a magnetosphere they run along the magnetic field lines as it is the point of least resistance. They move along these lines until they are destroyed by coming into contact with other particles. This usually happens around the poles of a planet where the magnetic field lines are concentrated and the atmosphere becomes thicker. The solar wind hits particles in the atmosphere at the poles, ionising them during the collision and releasing photons (packets of light) in the process. The colour of the resultant light emitted depends on the atmospheric particle: oxygen atoms give off a green light while nitrogen atoms emit blue or red light.

It is for these reasons that on Earth, and indeed on other planets in the Solar System, fantastic auroras appear at the poles. They don’t usually appear near the equator of a planet as the magnetic field lines of the magnetosphere are concentrated at the poles, although occasionally the intensity of the incoming solar wind can force the aurora quite far from the poles. As the solar wind continues to interact with a planet’s atmosphere more and more light is produced, often in sweeping waves or huge bands of light. For this reason, as Venus and Mars have insignificant magnetic fields, their auroras (if there are any at all) are virtually nonexistent and certainly very difficult to detect, while Mercury barely has an atmosphere and therefore does not have noticeable auroras.

To find out more about the fantastic auroras produced on Earth, Jupiter, Saturn, Uranus and Neptune check out issue 3 of All About Space, on sale now.

Image courtesy of NASA

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