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Astronomers finally uncover 40-year mystery of Jupiter's epic X-ray aurora flares

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For 40 years, Jupiter's intense aurora polaris, also known as northern and southern lights, have puzzled astronomers around the world. Now, scientists have finally uncovered the mystery behind the gas giant's epic X-ray flares. 

Using measurements taken by NASA's Juno spacecraft, which is orbiting Jupiter, and data from the European Space Agency's Earth-orbiting XMM-Newton mission, astronomers have been able to view the entire phenomenon from start to finish in a way they never could before. 

In a recent study published in the journal Science Advances, researchers detail the process, which includes electrically charged ions, responsible for the X-rays, "surfing" electromagnetic waves in the planet's magnetic field down into its atmosphere. 

Of all the light shows detected at the poles of seven planets in our solar system, Jupiter's are the most powerful, and the only ones produced by a gas giant. While some auroras can be spotted with the naked eye, others come in the form of short light wavelengths that can only be seen with certain telescopes. 

The purple hues in this image show X-ray emissions from Jupiter's auroras, detected by NASA's Chandra Space Telescope in 2007. They are overlaid on an image of Jupiter taken by NASA's Hubble Space Telescope.  (X-ray) NASA/CXC/SwRI/R.Gladstone et al.; (Optical) NASA/ESA/Hubble Heritage (AURA/STScI)

Earthlings are familiar with the northern lights, but Jupiter's version releases hundreds of gigawatts of energy, enough to briefly power all of humanity. These shorter emissions require a massive amount of energy to produce — leading scientists to wonder for the last four decades how Jupiter could generate them.

They knew the light shows were caused by ions entering Jupiter's atmosphere — but how did they get there? 

Researchers found the pulsating auroras are triggered by regular fluctuations in the planet's extremely strong magnetic field, which cause electromagnetic ion cyclotron (EMIC) waves. The particles, guided by the magnetic field, "ride the wave" across millions of miles of space before slamming into the planet's atmosphere — causing a burst of auroras every 27 minutes. 

"What we see in the Juno data is this beautiful chain of events. We see the compression happen, we see the EMIC wave triggered, we see the ions, and then we see a pulse of ions traveling along the field line," study co-author William Dunn said in a news release. "Then, a few minutes later, XMM sees a burst of X-rays."

Overlaid images of Jupiter's pole from NASA's satellite Juno and NASA's Chandra X-ray telescope. Left shows a projection of Jupiter's Northern X-ray aurora (purple) overlaid on a visible Junocam image of the North Pole. Right shows the Southern counterpart. NASA Chandra/Juno Wolk/Dunn

A similar process produces Earth's aurora. 

"It could, therefore, be a universal phenomenon, present across many different environments in space," Dunn said.

"Now we have identified this fundamental process, there is a wealth of possibilities for where it could be studied next," said co-lead author Dr. Zhonghua Yao. "Similar processes likely occur around Saturn, Uranus, Neptune and probably exoplanets as well, with different kinds of charged particles 'surfing' the waves." 

It's not clear why the magnetic field lines vibrate periodically, but they could be caused by interactions with solar wind or high-speed plasma flowing within Jupiter's very large magnetosphere. With Juno, astronomers now have the opportunity to delve even deeper. 

"X-rays are typically produced by extremely powerful and violent phenomena such as black holes and neutron stars, so it seems strange that mere planets produce them too," said co-author Graziella Branduardi-Raymont. "We can never visit black holes, as they are beyond space travel, but Jupiter is on our doorstep. With the arrival of the satellite Juno into Jupiter's orbit, astronomers now have a fantastic opportunity to study an environment that produces X-rays up close."

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