On July 5th, 2016 NASA's Jupiter probe arrived at the gas giant and began its four-year mission to study it. Since 1995 the Galileo probe has studied the system. The images and data it has sent back to Earth have revealed a lot about Jupiter.

Astronomers have been able to learn more about how Jupiter's moons interact with its atmosphere, and how the gas giant experiences the Northern and Southern lights. A team of researchers from the Southwest Research Institute observed how the streams of electrons from the largest moon in the solar system leave a footprint.

They looked at the data obtained by Juno on November 8th, 2020, when it passed through the intense beam of electrons that travel along the magnetic field line. They were able to gain new insight into the mysterious processes that create the shimmering lights by studying the particle population along this beam. The paper about their research was published.

Artist’s concept of aurorae on Ganymede – auroral belt shifting may indicate a subsurface saline ocean. Credit: NASA/ESA

The lead author of a paper outlining the results was a member of the Juno mission team. He explained in a recent press release.

“Jupiter’s most massive moons each create their own auroras on Jupiter’s north and south poles. Each auroral footprint, as we call them, is magnetically connected to their respective moon, kind of like a magnetic leash connected to the moon glowing on Jupiter itself.”

Solar particles reaching Earth's magnetosphere cause the Aurora Borealis and the Southern Lights. These particles are funneled by magnetic field lines towards the polar regions of Earth, where they produce dazzling displays of light. The situation is similar for Jupiter, where the electrons in the magnetosphere interact with the Molecules in its atmosphere.

Jupiter's atmosphere is more intense than Earth's, and its largest moons (Io, Europa, and Callisto) also experience the same. Dr. Jamey Szalay is a space physics research scientist.

“Prior to Juno, we knew that these emissions can be quite complex, ranging from a single auroral spot to multiple spots, which sometimes trail an auroral curtain that we called the footprint tail. Juno, flying extremely close to Jupiter, revealed these auroral spots to be even more complex than previously thought.”

The Juno mission’s instruments. Credit: NASA/SwRI

The role played by Ganymede in this activity is of particular interest because of its unique characteristic. Every moon in the Solar System has its own magnetic field. Similar to how a dynamo effect in Earth's interior leads to Earth's magnetosphere, the magnetic field on Ganymede is believed to be the result of tidal flexing.

Waves that accelerate electrons along the gas giant's magnetic field lines are created by the interaction between the smaller magnetosphere with Jupiter. The mission is able to study the particle environment using its Jovian Auroral Distributions Experiment (JADE), Ultraviolet Spectrometer (UVS), and Fluxgate.

JADE measured the electrons traveling along the magnetic field lines. The UV light it created when it reached Jupiter's atmosphere was measured in this way. The previous measurements showed that large magnetic perturbations accompanied the electron beams, but this time they didn't.

The findings might confirm a theory that has been around for a decade. The theory says that the multi-spot dance of the footprints is caused by the accelerated electrons along the beam. The end date for the mission was extended by NASA in January of 2021.

The JUpiter Icy Moons Explorer (JUICE) is scheduled to launch in 2023 and arrive around Jupiter in 2031. The mission will focus on the island of Ganymede. The next four years will be devoted to studying Europa exclusively, as NASA's Europa Clipper mission arrives around Jupiter.

The Jupiter-Ganymede relationship will be further explored by the extended mission from the European Space Agency.

Further reading on the topic.