ALIEN AURORA

This infrared image gives an unprecedented view of the southern aurora of Jupiter. The view is a mosaic of three images taken minutes apart as the craft was pulling away from Jupiter, after its first close approach. From Earth, the planet’s southern aurora can hardly be seen. It was captured by Juno’s Jovian Infrared Auroral Mapper ( JIRAM) on 27 August 2016. Auroras are ovals of light that occur when particles from the Sun strike molecules in a planet’s atmosphere and cause them to glow. The auroras appear as ovals because the magnetic field of the planet corrals the solar particles into a cone-shaped funnel that feeds them into the atmosphere around the planet’s magnetic poles. The same occurs at Earth, but as Jupiter’s magnetic field is the strongest planetary field in the Solar System – fully 20,000 times stronger than Earth’s – its auroras are stronger. This image is composed of wavelengths longer than visible light, ranging from 3.3 to 3.6 micrometres (one micrometre = one-thousandth of a millimetre). These wavelengths were chosen because they are the ones emitted by excited hydrogen ions. These are atoms that have lost an electron particle and dominate the planet’s atmosphere.