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An aurora over the northern polar region of Saturn as seen in different wavelengths of light by NASA’s Cassini spacecraft

© NASA/JPL/University of Arizona

PLANETS

Have we seen aurorae on other worlds?

Anyone who has ever witnessed an aurora atmosphere, near the poles. As the charged will know just how magnificent this natural phenomenon is. Sometimes forming a diffuse green glow on the poleward horizon, or if conditions are just right a spectacular overhead explosion of colour in the night sky, the privilege of witnessing an aurora first-hand is something many wish for.

Aurorae are the stunning result of a complex chain of interactions that start at the Sun. Solar particles travel outward from the Sun, in what is known as the solar wind, and interact with Earth’s magnetic field. While most of the solar wind is deflected by this magnetic barrier, under certain conditions, some of it can break through. These charged particles are then funnelled from inside our magnetic field down into our atmosphere, near the poles. As the charged particles interact with our atmospheric gases, they transfer energy to those gases, causing them to emit light of different colours.

But Earth isn’t unique in having aurorae. Other planets do too. In fact, any planet with a magnetic field and atmosphere will have its own aurorae. Thanks to spacecraft such as Cassini and the Hubble Space Telescope, we’ve been able to identify aurorae on many of the planets in our Solar System. The exact nature of these aurorae, such as their colour and size, is different from Earth’s, since their atmospheres and magnetospheres are different too.

Nathan Case is a senior research associate in space and planetary physics at Lancaster University