Alien Aurora: Lysak, Sulaiman and Elliott find new plasma regime in Jupiter’s aurora

Professor Robert Lysak, Assistant Professor Ali Sulaiman and Researcher Sadie Elliott, of the School of Physics and Astronomy recently published a paper in Physics Review Letters, “New Plasma Regime in Jupiter’s Auroral Zones,” on the first-ever detailed observation and analysis of a new type of plasma wave in Jupiter’s auroral zone. Their findings were featured in an article in the New Scientist magazine, under the headline “Astronomers found a completely new type of plasma wave near Jupiter.”

Sulaiman and Elliott brought their expertise in observation to data from NASA’s Juno probe, which made its historic low orbit flight over Jupiter’s north pole. “James Webb (Space telescope) has given us some infrared images of the aurora, but Juno is the first spacecraft in a polar orbit around Jupiter,” Sulaiman says.  What the astronomers observed was an entirely new phenomenon in auroral physics which has mainly been based on examples tuned to the magnetic field of the Earth. Jupiter by comparison is vastly more magnetic, due to its large size, fast rotation, and complex interactions with its moons.  The dynamo in the interior of Jupiter generates a field many times larger than that of Earth. 

Fig 1.

The space around these magnetized planets is filled with superheated particles that form a plasma, a state of matter where extremes of temperature cause the atoms to break into electrons and ions. These particles are accelerated down toward the planet, where they ignite gases in the upper atmosphere (on Earth, Oxygen and Nitrogen) leading to their familiar blue and green colors. Jupiter’s upper atmosphere is very different from Earth's and its aurora tends to be invisible to the naked eye and can only be observed with UV and Infrared instruments. 

The observational astronomers turned to Lysak, one of the world’s leading experts on these mechanics for help in describing the alien aurora. Plasma can exhibit the behavior of a fluid in that it travels in a wave. Unlike fluids, plasmas can have their own magnetic field and are influenced by external fields as well. Lysak studies Alfven Waves, a discipline named after Hannes Alfven who in 1942 first theorized that plasma could be understood by combining fluid mechanics with Electromagnetic field theory.

The data showed that due to the extremely low density of the plasma in Jupiter’s polar region, the frequency of the plasma waves was very low especially compared to the frequency of similar waves on Earth, combined with Jupiter’s supercharged magnetic field system, Juno showed a type of wave unlike anything ever observed before.

Figure 2

Lysak used what he called “basic plasma theory” to unpack the problem and to explain how combination of low plasma density and strong magnetic fields led to the new type of wave.  At Earth, the aurora forms a typical donut pattern of auroral activity around the polar cap shown in figure 2b, while the polar cap itself is usually dark. The complex mechanics of the Jupiter’s magnetic field intermittently allow these particles to flood into the zone over the polar caps as shown in Figure 2a. 

Elliott’s part of the project was to study how the field lines interact with upgoing electrons from the field lines which cause the plasma to diffuse out to 30 -50 times the radius of the gas giant. These electrons play a role in exciting the new plasma wave mode.  The group hopes to be able to learn more about this phenomenon when Juno makes further passes around Jupiter. Unfortunately, the planned extended mission to Jupiter is doubtful given the uncertain state of funding of the American space program, but they have some hope that JUICE and Europa Clipper, due to arrive at Jupiter at the end of the decade, may be able to accommodate this research.