All of the lights

The cause of Jupiter’s glowing “northern lights” is finally revealed

“Jupiter does this really weird thing where it pulses with a regular beat like clockwork.”

NASA/JPL-Caltech/Bertrand Bonfond

While looking through old data collected by the Juno spacecraft, William Dunn noticed something odd: Jupiter was pulsing every 27 minutes.

“It was just like pump — a burst of light — and then wait 27 minutes, chill out, and then another burst of light and wait 27 minutes, chill out, and then another burst of light,” Dunn, a research fellow at the University of London’s astrophysics group, tells Inverse.

This pattern, he and colleagues would later learn, was related to the planet’s mysterious auroras.

“It's kind of beautiful because you see this chain of events that lead up to the burst of light from the X-rays,” Dunn says.

Jupiter’s version of the northern lights was discovered nearly 40 years ago. Previously, scientists were unable to pin down the exact process causing the planet to display the brightest auroras of the Solar System.

In a study published Friday in the journal Science Advances, Dunn and his team offer an answer: It’s possible the phenomenon is caused by electromagnetic waves, which lead to the gathering of sulfur and oxygen ions over Jupiter’s poles.

What’s new — The Juno spacecraft launched in 2011 and orbits Jupiter every 53 days. Dunn and colleagues examined four years of its observations, as well as data pulled from the European Space Agency’s XMM-Newton X-ray telescope.

The X-ray telescope observes Jupiter’s X-ray auroras from Earth, while Juno measures whatever processes take place around Jupiter.

“Jupiter does this really weird thing where it pulses with a regular beat like clockwork,” Dunn says. “You can actually set your watch to it.”

In the combined observations, the team picked up on the chain of events taking place with the pulse that occurred every 27 minutes:

  • The first thing that happens is a little vibration of the magnetic field.
  • The vibration triggers electromagnetic ion cyclotron (EMIC) waves, also known as electromagnetic emissions, in the magnetosphere.
  • Those waves carry particles that surf their way toward the atmosphere, where they get dumped.
  • When those particles smash into the atmosphere, they produce X-rays
An illustration of the chain of events that lead to Jupiter’s powerful, bright auroras. Dunn et. al

“Honestly, since 2017 I've been looking at these datasets and trying to work out what's going on because there's so much crazy stuff,” Dunn says. “But after those four years, we can piece together this whole chain of events.”

Here’s the background — Auroras are colorful displays of light that shine in the sky when the Sun’s charged particles interact with a planet’s atmosphere.

On Earth, we have the aurora borealis (also known as the northern lights) and the aurora australis (the southern lights). The aurora borealis shines within the Arctic Circle, while the aurora australis shines casts across the Antarctic Circle.

Other planets in the Solar System also experience auroras. Jupiter, Saturn, Uranus, and Neptune all produce these colorful displays, while aurora-like phenomena created by slightly different forces have been spotted on Mars.

Jupiter has the brightest auroras in the Solar System. On both Earth and Jupiter, auroras are linked to charged particles in the planet’s magnetosphere — the region that surrounds a planet affected by its magnetic field.

But Jupiter’s magnetic field is about 20,000 times stronger than that of Earth’s.

Jupiter’s aurora resembles the same phenomenon over Earth’s polar regions.NASA/Newsmakers

“Jupiter is just a whole different beast [compared] to the Earth,” Dunn says.

Jupiter’s lights are also affected by a combination of the planet spinning really quickly — a day on Jupiter is only 10 hours long — and volcanic material pumped out by Jupiter’s moon Io.

“The rapid rotation, the really strong magnetic field and all of this volcanic stuff that IO is pumping out just like swells and blows Jupiter's magnetosphere to this crazy size,” Dunn says. “It’s a huge structure and there are so many crazy things going on.”

Why this discovery matters — Understanding a planet’s auroras helps scientists understand its magnetic field.

“The signature of magnetic fields is the northern lights on the planet,” Dunn says. “You can tell what processes are going on in that magnetic field and in the space environment around the planet.”

The Galileo spacecraft captured this image of a storm brewing on Jupiter in 1998.JPL/NASA/Getty Images

Magnetic fields are crucial to sustaining life on a planet. Earth’s strong magnetic field helps the planet sustain liquid water on its surface, making it possible for life to thrive.

As scientists hunt for habitable planets across the cosmos, magnetic fields are at the top of the list of requirements for said habitability.

What’s next — With the upcoming launch of the James Webb Space Telescope, scientists are hoping to get a better look at Jupiter’s auroras — as well as the auroras of Saturn, Uranus, and Neptune.

Dunn is also hoping for a future mission to Jupiter that uses an X-ray instrument to observe the auroras up close.

“Just seeing a planet in a whole new shade of light would reveal so many things that we just didn't even know about Jupiter,” he says.

Abstract: Jupiter’s rapidly rotating, strong magnetic field provides a natural laboratory that is key to understanding the dynamics of high-energy plasmas. Spectacular auroral x-ray flares are diagnostic of the most energetic processes governing magnetospheres but seemingly unique to Jupiter. Since their discovery 40 years ago, the processes that produce Jupiter’s x-ray flares have remained unknown. Here, we report simultaneous in situ satellite and space-based telescope observations that reveal the processes that produce Jupiter’s x-ray flares, showing surprising similarities to terrestrial ion aurora. Planetary-scale electromagnetic waves are observed to modulate electromagnetic ion cyclotron waves, periodically causing heavy ions to precipitate and produce Jupiter’s x-ray pulses. Our findings show that ion aurorae share common mechanisms across planetary systems, despite temporal, spatial, and energetic scales varying by orders of magnitude.
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