NASA’s Juno spacecraft orbiting Jupiter has solved a decades-old mystery by revealing that lightning strikes on the gas giant are similar to those on Earth to some extent.

Ever since the space agency’s Voyager spacecraft whizzed past the gas giant, scientists have noted evidence of lightning on Jupiter. The phenomenon, which has been theorized for centuries, prompted a number of questions including the origin of the lightning and how it is different from Earth, considering the unearthly nature of the gas giants.

Lightning on Jupiter
This artist’s concept of lightning distribution in Jupiter’s northern hemisphere incorporates a JunoCam image with artistic embellishments. Data from NASA’s Juno mission indicates that most of the lightning activity on Jupiter is near its poles. NASA/JPL-Caltech/SwRI/JunoCam

The mystery remained unsolved for almost 40 years because every spacecraft that flew by Jupiter during this period — Voyagers 1 and 2, Galileo, Cassini — recorded radio waves that didn’t match those produced by lightning on Earth.

“No matter what planet you’re on, lightning bolts act like radio transmitters — sending out radio waves when they flash across a sky,” Shannon Brown of NASA’s Jet Propulsion Laboratory and the lead author of the latest work said in a statement. The scientists expected to see low as well as high-energy radio emissions, like that on Earth, but there was no sign of the latter in the data.

“Many theories were offered up to explain it, but no one theory could ever get traction as the answer,” Brown said of the problem.

However, all of that changed completely when Juno, NASA’s latest mission to understand the turbulent environment of Jupiter, completed eight close flybys of the gassy planet. The spacecraft’s Microwave Radiometer, aka MWR instrument, detected as many as 377 lightning discharges during its orbit and found signs of the radio waves that had been undetected until now.

“They were recorded in the megahertz as well as gigahertz range [of the radio spectrum], which is what you can find with terrestrial lightning emissions,” Brown added. “We think the reason we are the only ones who can see it is because Juno is flying closer to the lighting than ever before, and we are searching at a radio frequency that passes easily through Jupiter’s ionosphere.”

Among other things, researchers from the Czech Academy of Sciences also found that lightning on the planet occurs just as frequently on Earth — another similarity. In another paper related to the findings from Juno, the researchers noted that the spacecraft’s Waves instrument detected six times more lightning than Voyager, with as many as four lightning strikes per second, just like the rate observed on Earth.

“Our unique orbit allows our spacecraft to fly closer to Jupiter than any other spacecraft in history, so the signal strength of what the planet is radiating out is a thousand times stronger,” Scott Bolton, Juno’s principal investigator, said in the statement. “Also, our microwave and plasma wave instruments are state-of-the-art, allowing us to pick out even weak lightning signals from the cacophony of radio emissions from Jupiter. “

That said, it is worth noting that while the nature and frequency of lightning strikes on Jupiter is more similar to Earth’s than scientists thought, the location of the phenomenon is completely different. On Earth, lightning bolts congregate near the equator, but in the Jovian environment, the same happens closer to the poles, more so in the northern hemisphere. “These findings could help to improve our understanding of the composition, circulation, and energy flows on Jupiter,” Brown concluded.

The findings could further get elaborated as Juno continues its work around Jupiter. The spacecraft will continue to orbit the planet till the early 2020s and is set to begin its 13th flyby of Jovian cloud tops next month.