Jupiter Puts on a Light Show For Juno

Jupiter boasts some of the most spectacular auroras in the solar system—vast, super-energetic fields of light that are permanently on display and bigger than planet Earth.

Lately, scientists say, the Jovian lights have been even more magnificent than usual. Researchers are matching up ultraviolet imagery taken by the Hubble telescope with data from spacecraft Juno, which is set to enter Jupiter’s orbit next week. Their goal is to better understand how the solar wind affects the planet’s auroras.

“These auroras are very dramatic and among the most active I have ever seen,” said Jonathan Nichols, an astronomist at the University of Leicester, in a statement on Thursday. “It almost seems as if Jupiter is throwing a firework party for the imminent arrival of Juno.”

The latest images build on an earlier collection of photos taken since Jupiter’s auroras were first discovered in 1979. “Some months ago, we thought we had some idea of what planets were like,” the planetary scientist Laurence Soderblom told newspapers at the time, “and we discovered how narrow our vision really was.”

Scientists already know that Jupiter’s auroras are caused by more than just solar storms. The planet’s gigantic magnetosphere also brightens the otherworldly lights with a constant stream of mega-intense charged particles. And all this is happening on a huge scale. Think of it this way: If Jupiter’s enormous magnetic field were visible to the eye, scientists say, it would appear from Earth to be the same size as the sun—even though it is five times farther away.

Jupiter also snags some additional charged particles from Io, one of its volcano-strewn moons. The gravitational tension between Jupiter and Io causes volcanic reactions on the moon, which then spews bursts of electrically charged atoms into space, further feeding Jupiter’s auroras.

If all goes as planned in the coming months, Juno will soon transmit a trove of information back to Earth that may help reveal more detail about the mechanics of Jupiter’s dazzling lights.

If it were possible to stand on the surface of the planet and look up, Jupiter’s auroras would ignite the entire sky. That is, of course, if you could see in ultraviolet. Mathias Jäger, a spokesman for ESA and Hubble, put it to me this way: “With the naked eye, the auroras would barley be visible—if at all.”

Then again, Juno may be able to catch a rare glimpse of Jupiter’s lights without ultraviolet assistance. ​If it does, they’re likely to appear red in color.

“We can't see the visible auroras from Earth as the planet's disc is too bright, but they've been observed in the night side by Galileo,” Nichols told me, referring to the spacecraft that traveled to Jupiter in the 1990s. “Hopefully Juno will get a great view from a vantage point above the poles!”