NASA/JPL-Caltech/SwRI/JunoCam
This artist's concept of lightning distribution in Jupiter's northern hemisphere incorporates a Juno image with artistic embellishments.
- NASA's Juno spacecraft has made an astonishing discovery about Jupiter's lightning strikes: They're similar to Earth's.
- Jupiter's lightning is clustered in the polar regions, while Earth experiences lightning more frequently around the equator.
- It's a longstanding mystery that could only have been solved with Juno.
NASA's Juno probe has unraveled the mystery of Jupiter's lightning - a problem that has vexed astronomers for close to four decades.
While "Jovian Lightning" had been theorized for centuries, it wasn't until 1979 that NASA's Voyager 1 spacecraft flew by Jupiter and confirmed the gas giant experiences lightning.
Jupiter's lightning, however, appeared different than thunderstorms here on Earth. When lightning strikes, it acts like a radio transmitter, blasting radio waves with each strike, according to NASA. But the lightning recorded by Voyager 1, and subsequent missions by other NASA spacecraft, didn't match the usual frequency of terrestrial lightning, confounding scientists.
A new paper published by NASA's Juno team in the journal Nature has found that Jupiter's lightning is actually much more similar to Earth's than previously thought.
"Until Juno, all the lightning signals recorded by spacecraft were limited to either visual detections or from the kilohertz range of the radio spectrum, despite a search for signals in the megahertz range," Shannon Brown, a scientist at NASA's Jet Propulsion Laboratory and a lead author on the paper, said. "Many theories were offered up to explain it, but no one theory could ever get traction as the answer."
On Earth, radio waves associated with lightning are in the megahertz range. Before Juno - which has been orbiting Jupiter since the summer of 2016 and has more sensitive instruments than older probes - the lightning on Jupiter was only recorded in the kilohertz range.
According to Brown, Juno picked up radio signals from Jupiter's lightning in the megahertz range experienced on Earth.
"We think the reason we are the only ones who can see it is because Juno is flying closer to the lightning than ever before, and we are searching at a radio frequency that passes easily through Jupiter's ionosphere," Brown said.
The team's finding was corroborated in a second paper, also published in Nature.
There is a key difference between Jupiter's lightning and Earth's, however. On our planet, lightning storms are clustered in the tropical regions around the equator. That's because warm air allows moisture to rise more freely through the atmosphere, fueling the thunderstorms that produce lightning, according to NASA.
On Jupiter, lightning is clustered in the polar regions - it's "inside-out" relative to Earth, Brown said.
Though Jupiter receives 25 times less sunlight than Earth, the Sun's rays do still heat up the gas giant's equator more than the poles. The Sun's heat creates just enough stability in the upper atmosphere around Jupiter's equator to inhibit the rise of warm air, preventing lightning-bearing clouds from forming above the planet's equator.
Jupiter's poles, which aren't warmed by the Sun, have a less stable atmosphere, according to NASA, which allows warm gases to rise and create the recipe needed to produce lightning.
"These discoveries could only happen with Juno," Scott Bolton, another author on the paper said. "Our unique orbit allows our spacecraft to fly closer to Jupiter than any other spacecraft in history."
Luckily for the scientists, NASA is extending the Juno mission through July 2021.