Earth is not the only world adorned with the glowing atmospheric phenomenon that is the Northern Lights. In fact, in a solar system aurora competition, the clear winner would be Jupiter. The so-called King of Planets is crowned with the most powerful auroras in the solar system and permanently orbits both poles.
Because they only glow in invisible wavelengths, we cannot see them with the naked eye, so it was not until 40 years ago that they were discovered. Ever since, researchers have wondered how these northern lights produce periodic bursts of X-rays.
Now they think they have solved it. Using simultaneous observations from the Jupiter probe Juno and the XMM-Newton X-ray Observatory, a team led by planetary scientist Zhonghua Yao of the Chinese Academy of Sciences in China has linked X-rays to vibrations in the gas giant̵
These vibrations generate waves in the plasma that propagate along the magnetic field lines, periodically causing heavy ions to rain down and collide with Jupiter’s atmosphere, releasing energy in the form of X-rays.
“We’ve seen Jupiter produce X-ray neuras for four decades, but we did not know how this happened. We only knew that they were produced when ions crashed into the planet’s atmosphere,” explained astrophysicist William Dunn of University College London in the United Kingdom.
“Now we know that these ions are transported by plasma waves – an explanation that has not been suggested before, although a similar process produces the Earth’s own northern lights. It may therefore be a universal phenomenon found in many different environments in space.”
Here on Earth, northern lights are generated by particles blowing in from the sun. They collide with the Earth’s magnetic field, which sends charged particles such as protons and electrons, which whiz along the magnetic field lines towards the poles, where they rain down on the Earth’s upper atmosphere and collide with atmospheric molecules. The resulting ionization of these molecules generates the amazing dancing lights.
On Jupiter, there are a few differences. The aurora are constant and permanent, as mentioned earlier; it is because the particles are not sun, but from the Jovian moon Io, the most volcanic world in the solar system. It constantly blows out sulfur dioxide, which is immediately removed via a complex gravitational interaction with the planet, becomes ionized and forms a plasma torus around Jupiter.
And then there are X-ray impulses. To find out how they were generated, the research team studied the planet using simultaneous observations from Juno and XMM-Newton, taken on 16-17. July 2017, a total of 26 hours. During this time, Jupiter fired an X-ray approximately every 27 minutes.
Based on these observations, the team linked Juno’s observations of the plasma with XMM-Newton’s observations of X-ray auroral bursts; with computer modeling, they determined how the two phenomena could be connected.
The team concluded that compressions in Jupiter’s magnetic field create oxygen and sulfur ion waves that spiral along the magnetic field lines toward Jupiter’s poles, where they rain down, collide with the atmosphere, and generate bursts of X-rays.
These waves are called electromagnetic ion cyclotron waves (or EMIC), and they have also been linked to flickering northern lights here on Earth.
It is unclear at this point what drives the compressions in Jupiter’s magnetic field. It can be the influence of the solar wind, circulation of heavy materials within the Jovian magnetosphere or surface waves on the magnetopause, the outer boundary between the magnetosphere and the surrounding plasma.
However, the compressions are generated, the fact that the same mechanism – EMIC waves – have been linked to auroral emissions in two very different worlds, suggests that it may be quite common in the solar system as well as in the galaxy outside.
“Now we have identified this basic process. There are a wealth of options for where it could be investigated next time, ”said Yao.
“Similar processes are likely to occur around Saturn, Uranus, Neptune and probably also exoplanets, where different kinds of charged particles ‘surf’ on the waves.”
The results show that EMIC waves could play an important, hitherto unnoticed role in the ion dynamics of Jupiter’s atmosphere and could help us better understand plasma processes across the galaxy.
The research is published in Scientific progress.