Cassini Flies Through Saturn’s Aurora

by Nancy Atkinson on September 24, 2010

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Saturn’s mysterious aurora has fascinated astronomers and space enthusiasts since it was first observed back in 1979. Now, the Cassini spacecraft has made the first observations from within the giant radio aurora of Saturn. The spacecraft flew through an active auroral region in 2008, and scientists say there are both similarities and contrasts between the radio auroral emissions generated at Saturn and those at Earth. Additionally, Cassini’s visual and infrared mapping spectrometer instrument (VIMS) took data to create a new movie (above) showing Saturn’s shimmering aurora over a two-day period. All this new data are helping scientists understand what drives some of the solar system’s most impressive light shows.

Cassini crossed the radio aurora of Saturn on 17 October 2008, at a distance of 4 Saturn's radii above the atmosphere. These radio emissions, generated by fast electrons, are strongly beamed. They were characterised by simultaneous observations of three different experiments. Credit: NASA/JPL/University of Iowa/CNES/Observatoire de Paris

“So far, this is a unique event,” said Dr. Laurent Lamy at the European Planetary Science Congress in Rome this week. “Whereas the source region of Earth’s radio aurora has been studied by many missions, this is our first opportunity to observe the equivalent region at Saturn from the inside. From this single encounter, we have been able to build up a detailed snapshot of auroral activity using three of Cassini’s instruments. This gives us a fascinating insight into the processes that are generating Saturn’s radio aurora.”

See an animation created from the radio instrument on Cassini at this link. On the left hand side are the radio sources as seen from Cassini. The right hand side shows the projection of the radio sources down onto the southern pole of the planet. Credit: NASA/JPL/University of Iowa/CNES/Observatoire de Paris

Separately, Tom Stallard, lead scientist on a joint VIMS and Cassini magnetometer collaboration, presented the VIMS movie at the conference.

Source: European Planetary Science Congress

In the movie, the aurora phenomenon clearly varies significantly over the course of a Saturnian day, which lasts around 10 hours 47 minutes. On the noon and midnight sides (left and right sides of the images, respectively), the aurora can be seen to brighten significantly for periods of several hours, suggesting the brightening is connected with the angle of the sun. Other features can be seen to rotate with the planet, reappearing at the same time and the same place on the second day, suggesting that these are directly controlled by the orientation of Saturn’s magnetic field.

Image of Saturn’s aurora seen at ultraviolet wavelengths. The spiral shape seen here is similar to the distorted radio aurora visualised by the team and also indicates enhanced auroral activity. Credit: ESA/NASA/Hubble

“Saturn’s auroras are very complex and we are only just beginning to understand all the factors involved,” Stallard said. “This study will provide a broader view of the wide variety of different auroral features that can be seen, and will allow us to better understand what controls these changes in appearance.”
Auroras on Saturn occur in a process similar to Earth’s northern and southern lights. Particles from the solar wind are channeled by Saturn’s magnetic field toward the planet’s poles, where they interact with electrically charged gas (plasma) in the upper atmosphere and emit light. At Saturn, however, auroral features can also be caused by electromagnetic waves generated when the planet’s moons move through the plasma that fills Saturn’s magnetosphere.

This false-color composite image shows Saturn’s rings and southern hemisphere. The composite image was made from 65 individual observations by Cassini’s visual and infrared mapping spectrometer in the near-infrared portion of the light spectrum on Nov. 1, 2008. Credit: NASA/JPL/University of Arizona

About 

Nancy Atkinson is Universe Today's Senior Editor. She also is the host of the NASA Lunar Science Institute podcast and works with Astronomy Cast. Nancy is also a NASA/JPL Solar System Ambassador.

Aqua September 24, 2010 at 8:27 AM

Very interesting! In a related(?) story: Today, NASA Science chatted up a finding from the Stereo spacecraft that indicates that CME’s from Sol are ‘steered’ back into the sun’s equatorial plane by magnetic field lines which more or less ‘direct’ energy to the plane of the solar system’s planets.

http://science.nasa.gov/science-news/science-at-nasa/2010/21sep_zigzag/

THAT story seems to indicate that Saturn’s rings may also be ‘shepherded’ into their extremely flat orientation not only by gravitational forces but also by Saturn’s very ‘rotationally aligned’ magnetic field? Superconducting cryogenic ice particles anyone?

Aqua September 25, 2010 at 8:50 AM

The link, “See the animation created from the radio instrument on Cassini at this link” does not work… Instead one sees “Error 404″

Aqua September 25, 2010 at 8:57 AM

In the second image, by NASA/JPL/University of Iowa/CNES/Observatoire de Paris, the Huygens Titan probe is shown still attached to Cassini…. which is not the configuration on 17 October 2008.

Oh well… in a perfect world there would be several ‘Cassini-like’ missions at Jupiter, Saturn, Uranus and Neptune!

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