Ever since NASA’s Voyager 1 spacecraft flew past Jupiter in March, 1979, scientists have wondered about the origin of Jupiter’s lightning. That encounter confirmed the existence of Jovian lightning, which had been theorised for centuries. But when the venerable explorer hurtled by, the data showed that the lightning-associated radio signals didn’t match the details of the radio signals produced by lightning here at Earth.
In a new paper published in astronomy journal Nature, scientists from NASA’s Juno mission describe the ways in which lightning on Jupiter is actually analogous to Earth’s lightning. Although, in some ways, the two types of lightning are polar opposites.
“But until Juno, all the lightning signals recorded by spacecraft [Voyagers 1 and 2, Galileo, Cassini] were limited to either visual detections or from the kilohertz range of the radio spectrum, despite a search for signals in the megahertz range. Many theories were offered up to explain it, but no one theory could ever get traction as the answer,” said Shannon Brown of NASA’s Jet Propulsion Laboratory, a Juno scientist and lead author of the paper published in Nature and Nature Astronomy respectively.
Enter Juno, which has been orbiting Jupiter since July 4, 2016. “In the data from our first eight flybys, Juno’s MWR detected 377 lightning discharges,” said Brown. “They were recorded in the megahertz as well as gigahertz range, which is what you can find with terrestrial lightning emissions. 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.”
While the revelation showed how Jupiter lightning is similar to Earth’s, the new paper also notes that where these lightning bolts flash on each planet is actually quite different. “Jupiter lightning distribution is inside out relative to Earth,” said Brown. “There is a lot of activity near Jupiter’s poles but none near the equator.”
In a second Juno lightning paper published in Nature Astronomy, Ivana Kolmašová and colleagues, presented the largest database of lightning-generated low-frequency radio emissions around Jupiter (whistlers) to date.
The team recorded over 1,600 of the signals, compared to just 167 collected by Voyager 1. Together, these findings represent the most detailed and comprehensive look at Jupiter's lightning to date, and provide important clues to figuring out the complex dynamics hidden by the planet's opaque layers of stormy clouds.