Saturn Has Auroras Too, and They're Beautiful

Auroras are pretty incredible phenomena, wherein charged particles from the Sun collide with atoms in the upper layers of the atmosphere, producing incredible light displays. But they're not limited to Earth: Last year NASA managed to see the light display from auroras on Saturn with two spacecraft in two different wavelengths. The images were released this week, and they're beautiful. Better yet, the images are helping scientists understand how outbursts from the Sun interact with the ringed planet.

NASA has a lot of eyes in the sky at the moment, and they all see in different wavelengths. Last April and May, the agency turned some of those eyes on Saturn. The Hubble Space Telescope and the Cassini spacecraft both watched the aurora, the latter had a front row seat from inside Saturn’s system.

The first set of images are ultraviolet images from Hubble showing an active aurora dancing around Saturn’s north pole. The level of activity was high in early April then calmed down before picking up again towards the end of May. A second set of ultraviolet images shows an aurora around the north pole up close. It was taken by the Cassini spacecraft just six Saturn radii (about 220,000 miles) away. The last set of images were taken in the infrared and they show a more quiet aurora around the souther pole again as seen by Cassini.

The views are striking, but more importantly they tell scientists a lot about the ringed planet, particularly the images from Cassini. Using the spacecraft’s ultraviolet imaging spectrometer from such a close position, its images show scientists the changing patterns of faint emissions produced during the light storm. These images also allowed scientists to link changes in the auroras to fluctuations to solar activity.

Ultraviolet images from Cassini suggests that Saturn’s bright auroral storms may be rooted in connections between the planet’s magnetic field lines, the same process that can cause storms in the magnetic bubble that surrounds the Earth. The images also showed scientists a persistent bright patch of the aurora rotating in step with its moon Mimas, almost as though it was tidally locked to the satellite. This isn’t the first time auroral light has been linked to a moon. Previous imaging of auroral storms have shown bright spots linked to the moon Enceladus.

"This is our best look yet at the rapidly changing patterns of auroral emission," said Wayne Pryor, one of Cassini’s co-investigator from Central Arizona College. "Some bright spots come and go from image to image. Other bright features persist and rotate around the pole, but at a rate slower than Saturn's rotation."

This new data is also shedding light on mysteries about the giant planet’s atmosphere. "Scientists have wondered why the high atmospheres of Saturn and other gas giants are heated far beyond what might normally be expected by their distance from the sun," said Sarah Badman, a Cassini visual and infrared mapping spectrometer team member from  Lancaster University in England. "By looking at these long sequences of images taken by different instruments, we can discover where the aurora heats the atmosphere as the particles dive into it and how long the cooking occurs.”

Some of the clues are in the colors of the auroras as seen in the visible light spectrum. On Earth, we see auroras that look to be stretched vertically coloured green at the bottom and red at the top. Images from Cassini showed similarly vertically shaped aurora on Saturn but with different colors: red at the bottom and purple at the top. The difference in colour is a hint about the atmospheric composition. The auroras on Earth are dominated by excited nitrogen and oxygen molecules while on Saturn the auroras are dominated by excited hydrogen molecules.

"While we expected to see some red in Saturn's aurora because hydrogen emits some red light when it gets excited, we also knew there could be color variations depending on the energies of the charged particles bombarding the atmosphere and the density of the atmosphere," Ulyana Dyudina, an imaging team associate at the California Institute of Technology. "We were thrilled to learn about this colorful display that no one had seen before."

Scientists hope additional Cassini data will explain how clouds of charged particles move around the planet as it spins, how these clouds interact with solar material. And now is the perfect time to be looking. We’re currently at the peak of a solar cycle meaning the Sun is at its most active. Which means there’s more work to do.

Scientists are still analyzing data gathered at the same time by ground-based telescopes, which will hopefully explain how particles are ionized in Saturn's upper atmosphere. This will be a huge step in understanding Saturn. Scientists have been observing Saturn from the ground for years, and having an understanding of what’s going on with that planet’s atmosphere will help them separate the disturbances of our own atmosphere from events happening on Saturn.