Jupiter auroras
Jupiter's moons leave strange footprints on its auroras. Pictured, an image composite of two different Hubble observations. The auroras were photographed during a series of Hubble Space Telescope Imaging Spectrograph far-ultraviolet-light observations taking place as NASA's Juno spacecraft approaches and enters into orbit around Jupiter. The full-color disk of Jupiter in this image was separately photographed at a different time by Hubble's Outer Planet Atmospheres Legacy (OPAL) program, a long-term Hubble project that annually captures global maps of the outer planets. NASA, ESA, and J. Nichols (University of Leicester)

When it comes to sky-watching, none of us can deny the beauty of auroras that put up an amazing show on the poles of our planet. Streamers of green, red, blue, and purple light make a mesmerizing display, which many refer to as aurora borealis or northern lights and aurora australis or southern lights.

However, our Earth isn’t the only planet to produce these spectacular shows. The phenomenon is a result of sun’s electrically charged particles’ traveling down the magnetic field lines and interacting with the upper atmosphere, which means any planet hosting an atmosphere and magnetic field can witness the same.

“It's not very different from a neon lamp,” Alessandro Mura, a researcher at Italy’s National Institute for Astrophysics, told Newsweek. “Electrons hit the gas and excite it, then the gas shows some luminescence.”

Astronomers have already seen auroras on Jupiter and Saturn, but recently, Mura and colleagues scouring through the data captured by Juno — NASA’s spacecraft that has been orbiting Jupiter since 2012 — revealed light shows in Jovian skies are surrounded by strange “footprints” or small emission features associated with the gas giant's moons.

On Jupiter, the electrons producing auroras come from the magnetosphere, a layer of plasma and magnetic field surrounding the planet. Previous studies suggested the interaction between planet’s moons and magnetosphere formed some “footprints,” but they were not seen in detail until Juno’s infrared auroral mapper imaged the light show on the gas-giant.

“During Orbit 8 [in] September of 2017, we decided to look close, very, very close to the footprint of Io,” Mura told Space.com. “We were not expecting anything special, because so far there was no particular reason why to expect anything different than a big spot.”

However, the photographs revealed Jovian moon Io created evenly spaced bright spots — as big as the moon itself — that looked like a trail of swirling vortices in both hemispheres. They streaked for hundreds of kilometers and appeared to split into two arcs well below the main auroras.

The researchers also spotted that Galilean moon Ganymede, which is much bigger than Mercury in size, also generates double footprint on the auroras seen the planet. The features, separated by a distance of 100km, was never been seen before and according to the team, it can provide them with a measure into the moon’s own magnetosphere.

These features, as the researchers think, occur due to the orbital path of the moons in question. Both Io and Ganymede are so close to the planet that they travel through the magnetosphere. This movement triggers an interaction with the plasma and drives extra electrons contributing to the features seen in these images. They are not visible to the naked eye but can be detected by infrared and UV sensors, just like how Juno did.

That said, further observations from the spacecraft could help the team understand why the moons create their own different patterns like lo’s swirling trail.

“Io, being the closest [moon to Jupiter], has the most intense footprint,” Mura added. “Io is so close that tracing the magnetic field from Io to Jupiter is a very powerful tool to understanding the magnetic field.”