The mystery of Jupiter’s fixed aurora borealis is finally solved after 40 years

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Earth is not the only world adorned with the glowing atmospheric phenomenon, the aurora borealis. Indeed, in the aurora borealis competition for the solar system, Jupiter will be the clear winner. The so-called king of the planets culminates in the most powerful aurora borealis in the solar system, revolving permanently around its poles.

Since they only glow in invisible wavelengths, we can’t see them with the naked eye, so they were only discovered 40 years ago. Since then, scientists have wondered how these aurora borealis produce periodic bursts of X-rays.

Now, they think they’ve solved it. Using simultaneous observations from the Jupiter probe Juno and the X-ray space observatory XMM-Newton, a team led by planetary scientist Zhonghua Yao of the Chinese Academy of Sciences in China correlated the X-ray bursts with vibrations in the gas giant’s magnetic field lines.

These vibrations generate waves in the plasma that propagate along magnetic field lines, periodically causing heavy ions to fall off and collide with Jupiter’s atmosphere, releasing energy in the form of X-rays.

“We’ve seen Jupiter produce X-ray auroras for four decades, but we didn’t know how they happened. We only knew that they were produced when ions collided with the planet’s atmosphere,” explained astrophysicist William Dunn of University College London in the United Kingdom. .

“We now know that these ions are transported by plasma waves – an explanation that has not been proposed before, although a similar process produces Earth’s aurora borealis. Thus, they could be a global phenomenon, present across many different environments in space.”

Here on Earth, the aurora borealis are generated by particles blowing from the sun. They collide with Earth’s magnetic field, which sends charged particles such as protons and electrons rushing along magnetic field lines toward the poles, where they rain down on Earth’s upper atmosphere and collide with atmospheric particles. The resulting ionization of these particles generates amazing dancing lights.

On Jupiter, there are some differences. The aurora borealis is constant and permanent, as noted earlier; That’s because the particles are not solar, but from Jovian’s moon Io, the most volcanic world in the solar system. It constantly emits sulfur dioxide, which is instantly stripped away by a complex gravitational interaction with the planet, ionizing and forming a plasma torus around Jupiter.

Then there are the X-ray pulses. To find out how it was generated, the research team studied the planet, using simultaneous observations from Juno and XMM-Newton, captured on July 16-17, 2017, for 26 hours. During this time, Jupiter was shooting x-rays approximately every 27 minutes.

Based on these observations, the team linked Juno’s plasma observations to XMM-Newton observations of X-ray auroral bursts. With computer modeling, they determined how the two phenomena might be linked.

The team concluded that compressions in Jupiter’s magnetic field create waves of oxygen and sulfur ions circulating along magnetic field lines toward Jupiter’s poles, where they fall off and collide with the atmosphere and generate bursts of X-ray light.

These waves are called electromagnetic ionic cyclotron (or emic) waves, and they have also been linked to the flashing aurora borealis here on Earth.

At this point, it’s not clear what drives the pressures in Jupiter’s magnetic field. It could be the effect of the solar wind, the rotation of heavy materials within the Jovian magnetosphere, or surface waves at magnetic shutdown, the outer boundary between the magnetosphere and the surrounding plasma.

However pressure is created, the fact that the same mechanism – EMIC waves – has been linked to auroral emissions in two very different worlds suggests that it may be very common in the Solar System, as well as in the galaxy beyond.

“Now that we have identified this basic process, there is an abundance of possibilities where it can be studied next,” Yao said.

“Similar processes are likely to occur around Saturn, Uranus, Neptune and possibly the exoplanets as well, with different types of charged particles ‘surfing’ the waves.”

The results show that EMIC waves can play an important, hitherto unnoticed role in Jupiter’s atmospheric ion dynamics, and can help us better understand plasma processes across the galaxy.

The research was published in the journal Science Advances.

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