Jupiter study reveals independent pulses of X-ray auroras

The northern and southern lights of Jupiter pulse independently - unlike the Earth’s auroras - according to new research which includes expertise from the University of Southampton.

The study, published in Nature Astronomy, used the European Space Agency’s XMM-Newton and NASA’s Chandra X-ray observatories to make discoveries that could support the understanding of other bodies across the Universe such as brown dwarfs, exoplanets and even neutron stars.

Dr Caitriona Jackman, an Associate Professor of Space Physics at Southampton’s Department of Physics and Astronomy, contributed to the study which was led by Dr William Dunn from University College London (UCL).

The study found that very high-energy X-ray emissions at Jupiter’s south pole consistently pulse every 11 minutes. Meanwhile those at the north pole are erratic: increasing and decreasing in brightness, independent of the south pole.

This behaviour is distinct from Earth’s north and south auroras which broadly mirror each other in activity. Other similarly large planets, such as Saturn, do not produce any detectable X-ray aurora, which makes the findings at Jupiter particularly puzzling.

“Jupiter’s auroral X-ray emissions are the most powerful in our solar system, and their study provides unique insight into the origin, dynamics and acceleration of charged particles in the Jovian magnetosphere,” Caitriona explains. “Now is a fantastic time to study Jupiter, as the Juno spacecraft is taking high resolution in situ measurements of the magnetic field and particles which can help to constrain our theories of what causes the powerful X-rays.”

Since arriving at Jupiter in 2016, the Juno mission has been re-writing much of what is known about the giant planet, but the spacecraft does not have an X-ray instrument on board. To understand how the X-ray aurora are produced, the team hope to combine the X-ray aurora information gathered using XMM-Newton and Chandra with data collected by Juno as it explores the regions producing Jupiter’s aurora.

One of the theories that Juno may help to prove or disprove is that Jupiter’s auroras form separately when the planet’s magnetic field interacts with the solar wind. The team suspect that the magnetic field lines vibrate, producing waves that carry charged particles towards the poles and these change in speed and direction of travel until they collide with Jupiter’s atmosphere, generating X-ray pulses.

The UCL and Harvard-Smithsonian-led study also involved researchers from Lancaster University, NASA Marshall Space Flight Center, Universite de Liege, Boston University, Southwest Research Institute (SwRI), Jet Propulsion Laboratory, Caltech, MIT and Universidad Pontificia Comillas. It was funded by the Science and Technology Facilities Council (STFC), ESA, the Natural and Environmental Research Council (NERC) and UCL.

Click here to download the paper ‘The independent pulsations of Jupiter’s northern and southern X-ray auroras’ (DOI10.1038/s41550-017-0262-6, Nature Astronomy).