A New Type of Aurora Found on Saturn Resolves a Planetary Mystery

Earth’s northern and southern lights—the results of a rendezvous between magnetic fields, energized particles from the Solar, and our planet’s atmospheric admixture—are wondrous spectacles. However Earth doesn’t maintain a monopoly on auroras. They exist on different worlds with magnetic fields, together with Saturn, whose auroral glow shimmers within the infrared and ultraviolet.

Now, as revealed by a latest research printed within the journal Geophysical Analysis Letters, scientists have found an aurora on that ringed world that’s not like some other. Like Earth’s, Saturn’s northern lights are fueled by a bathe of energized particles from the heavens. However a few of its auroras solely make an look when screaming winds shoot throughout the north pole—a bit like a gust of air stirring up a cosmic bonfire.

“To my data, [this is the] first time an aurora pushed by atmospheric winds has been detected,” says Rosie Johnson, an area physics researcher at Aberystwyth College in Wales who isn’t concerned with the research. “It’s a extremely nice outcome!”

It additionally occurs to be a revelation that took place whereas scientists puzzled over a seemingly innocuous query: Why can’t we work out how lengthy a day lasts on Saturn? Because it seems, it solely took 40 years, a spacecraft with a demise want, ice volcanoes, and a telescope atop a Hawaiian mountain to seek out out.

Earth makes it straightforward to measure how lengthy a day lasts: 24 hours. That’s as a result of our planet is roofed in readily identifiable, mounted landmarks. All an extraterrestrial viewer must do is tag a kind of, anticipate it to rotate out of sight after which return to view, and voilà: That’s how lengthy it takes Earth to make one full rotation on its axis.

You possibly can’t do that for worlds the place the surfaces are obfuscated by thick gaseous veils, like Jupiter, Saturn, Uranus, and Neptune. Fortuitously, all of them have magnetic fields rooted to their geologic hearts, shields that defend their atmospheres from being stripped away by the photo voltaic wind. These magnetic fields have charged particles scooting up and down them, emitting radio pulses as they go. As planets rotate, so do their magnetic fields, which take this radio pulse sign alongside for the experience.

Consider these planets like radio “lighthouses”—after they make one full rotation, so does the radio beam sweeping from them. A distant observer can “see” a shiny radio sign spinning round within the darkness. “You are able to do this for Uranus and Neptune. It’s additionally been finished for the Earth. It really works,” says James O’Donoghue, a planetary astronomer on the Japan Aerospace Exploration Company and coauthor of the brand new research.

Not so for Saturn.

Ever for the reason that two Voyager probes took a detailed take a look at Saturn within the early Nineteen Eighties, numerous spacecraft have tried measuring the spin of its radio lighthouse to find out the size of a Saturnian day. However each time it has been measured, the size of a day appears to vary, with values ranging between 10.5 Earth hours to 10.9 Earth hours. The Cassini spacecraft, which entered Saturn’s orbit in 2004 and stayed there till 2017, realized extra about this resplendent fuel large than some other mechanical customer—however it nonetheless couldn’t work out how lengthy a day was. “It simply discovered extra issues,” says O’Donoghue.

Video: James O’Donoghue

What did grow to be clear throughout its tenure, although, was that Saturn appeared to have three completely different radio lighthouses. The majority of the planet had one, however its north and south poles every possessed their very own, spinning at completely different charges. That will need to have been why the size of Saturn’s day appeared to maintain altering.

However why does Saturn have a number of lighthouses? “Lots of people had theories. It was a kind of late-night pub discussions, you understand,” says Tom Stallard, a planetary astronomer on the College of Leicester and a co-author of the brand new research. Some individuals thought it had one thing to do with the way in which the planet’s magnetic subject was being generated. Others puzzled if the reply was hiding inside Saturn’s tempestuous environment.