Juno reveals details about lightning on Jupiter

Giant planet's lightning is concentrated at its poles.
By Laurel Kornfeld | Feb 09, 2019
NASA's Juno spacecraft has given scientists new insight into Jupiter's strange lightning, about which scientists theorized for centuries before Voyager 1 confirmed its existence during its 1979 flyby.

Juno's suite of sensitive science instruments, including its JunoCam camera and Microwave Radiometer Instrument (MWR), which records planetary emissions across several frequencies, observed lightning on Jupiter at close range, finding both similarities and differences compared with lightning on Earth.

While lightning always produces radio signals, the signals it generates on Jupiter do not match those generated by Earth's lightning.

"No matter what planet you're on, lightning bolts act like radio transmitters--sending out radio waves when they flash across the sky. 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," reported Juno scientist Shannon Brown of NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California.

MWR detected 377 discharges of lightning during Juno's first eight close flybys of Jupiter, she noted. As with lightning on Earth, emissions were produced in both the megahertz and gigahertz ranges. Unlike any other spacecraft, Juno is capable of detecting these emissions because it is flying very close to the planet and observing in a radio frequency that passes through its ionosphere, Brown said.

Unlike Earth, where lightning is most common at the equator, Jupiter has its lightning concentrated at its poles and non-existent at its equator. In both cases, the driving force is heat.

Earth's heat source is solar radiation, which is strongest at its tropics. Through the process of convection, warm tropical air rises, fueling the thunderstorms in which lightning occurs.

In contrast, Jupiter, which is five times further from the Sun than Earth, receives the majority of its heat from internal sources rather than from the Sun.

The giant planet receives 25 times less sunlight than does Earth. That sunlight generates the most heat at Jupiter's equator. But instead of causing warm air there to rise, solar radiation stabilizes the upper atmosphere in Jupiter's tropical regions, preventing the warm air from rising.

Jupiter's poles, which do not receive this warmth, lack this atmospheric stability, enabling warm gases to rise via convection and creating conditions favorable for lightning to occur.

"These findings could help improve our understanding of the composition, circulation, and energy flows on Jupiter," Brown emphasized.

Findings of the study have been published in the journal Nature.






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