EPSC 2010 – Two days in the life of Saturn’s aurora
September 24, 2010

Two days in the life of Saturn’s aurora – the movie


A new animation and images showing Saturn’s shimmering aurora over two days is helping scientists understand what drives some of the Solar System’s most impressive light-shows. The movie is part of a new study of the entire catalogue of images of Saturn taken by Cassini’s visual and infrared mapping spectrometer (VIMS) instrument, which have been processed to extract auroral information.  Preliminary results will be presented by Dr Tom Stallard at the European Planetary Science Congress in Rome on Friday 24th September.

“Cassini’s instruments have been imaging the aurora in magnificent detail, but to understand the overall nature of the auroral region we need to make a huge number of observations – which can be difficult because Cassini observation time is in high demand.  However, there are VIMS observations of numerous other scientific targets that also include auroral information.  Sometimes the aurora can be clearly seen, sometimes we have to add multiple images together to produce a signal.  But as a whole, this wide set of observations will allow us to understand the aurora in general, rather than the beautiful specific cases that dedicated auroral observations allow,” said Stallard (University of Leicester, UK) who is part of an international team carrying out the study.

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

As with Earth’s Northern and Southern Lights, particles from the solar wind are channelled 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.  However, auroral features at Saturn can also be caused by electromagnetic waves generated when its moons move through the plasma that fills Saturn’s magnetosphere.

To date, Stallard and his colleagues have investigated around 1000 images from the 7000 that VIMS has taken to date of Saturn’s auroral region.

“Saturn’s aurora are very complex and we are only just beginning to understand all the factors involved.  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.” said Stallard.

Astronomers at the Royal Observatory, Greenwich, have also brought this new view of the ringed planet to the planetarium dome. The images and animations will be included in the interactive show “Meet the Neighbours” produced for the Peter Harrison Planetarium and be seen by audiences who choose to explore Saturn.

Dr Marek Kukula, Public Astronomer at the Royal Observatory, said “We’re very excited to be displaying these spectacular new images of Saturn in our planetarium. The Royal Observatory has 1.6 million visitors every year and we’re always keen to bring our audiences the very latest discoveries in space. We’re particularly pleased to be working so closely with Europe’s Planetary Science community.”


The videos and tiff files of the images can be downloaded from www.tomstallard.com/saturn.zip

All the images (and video) share the same false-colour scheme.
• Blue represents reflected sunlight that bounces off the rings and the ‘surface’ of Saturn – cloud layers that float at an air pressure similar to that found at the surface on Earth.  This is reflected sunlight near 1 micron and is useful here because it shows the direction of the Sun in each image.
• Green represents the auroral emission, a composite of several wavelengths (between 3-4 micron), from the H3+ molecule. This aurora glows about 1000km above the planet’s surface.
• Red represents the thermal emission from below the clouds (near 5 micron), the heat from the interior of Saturn showing the deeper weather systems of the planet (including the famous hexagon in the north).


Image 1: Composite image made up of 65 individual VIMS observations, each six minutes long (1 November 2008).  The mosaic shows the entire planet, including the rings as seen by Cassini from the south.  Credit: NASA/JPL/University of Leicester/University of Arizona


Image 2: Four composite views of Saturn taken on 24 May 2007.  Credit: NASA/JPL/University of Leicester/University of Arizona

Video 1:  Saturn’s auroral region over approximately 20 hours, just under two Saturnian days, from 2:15 p.m. UTC on Sept. 22, 2007 to 10:53 a.m. on Sept. 23, 2007. The spacecraft viewing angle stays the same, so that throughout the video, the blue of the reflected sunlight stays in the same place, but you can clearly see the planet’s interior (in red) rotating underneath.  The aurora can clearly be seen to vary significantly over the period of the observation.  On the noon and midnight sides (left and right, respectively) the aurora can be seen to brighten significantly for extended periods of several hours, suggesting the brightening is connected with the direction of the sun, whereas other features can clearly be seen to rotate with the underlying planet, suggesting that these are directly controlled by the direction of Saturn’s magnetic field. Credit: NASA/JPL/University of Leicester/University of Arizona
Download from www.tomstallard.com/saturn.zip

Video 2:  Like Video 1,  these images were taken between 2:15 p.m. UTC on Sept. 22, 2007 to 10:53 a.m. on Sept. 23, 2007. In this video, the two separate days are shown one above the other, with features from the planet’s interior (in red) lined up.  This clearly shows that the auroral emission follows a similar pattern on each day, with an auroral brightening rotating around with the planet. Credit: NASA/JPL/University of Leicester/University of Arizona.
Download from www.tomstallard.com/saturn.zip


The Visual and Infrared Mapping Spectrometer instrument (VIMS) is one of 12 instruments onboard NASA’s Cassini spacecraft.  The VIMS team is led by Robert H. Brown of the University of Arizona. The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. NASA’s Jet Propulsion Laboratory, Pasadena, Calif., manages the mission for NASA’s Science Mission Directorate, Washington, D.C.

VIMS homepage: http://wwwvims.lpl.arizona.edu/
Cassini homepages: http://www.nasa.gov/cassini and saturn.jpl.nasa.gov

EPSC 2010 is organised by Europlanet, a Research Infrastructure funded under the European Commission’s Framework 7 Programme, in association with the European Geosciences Union, with the support of the Italian National Institute for Astrophysics (INAF) and the INAF Institute of Physics of Interplanetary Space (IFSI) in Rome.  EPSC is the major meeting in Europe for planetary scientists. The 2010 programme comprises 48 sessions and workshops covering a wide range of planetary topics.
EPSC 2010 is taking place at the Angelicum Centre – Pontifical University of Saint Thomas Aquinas, Rome, Italy from Sunday 19 September to Friday 24 September 2010.
For further details, see the meeting website:

Europlanet Research RI is a major (€6 million) programme co-funded by the European Union under the Seventh Framework Programme of the European Commission.
Europlanet RI brings together the European planetary science community through a range of Networking Activities, aimed at fostering a culture of cooperation in the field of planetary sciences, Transnational Access Activities, providing European researchers with access to a range of laboratory and field site facilities tailored to the needs of planetary research, as well as on-line access to the available planetary science data, information and software tools, through the Integrated and Distributed Information Service.   These programmes are underpinned by Joint Research Activities, which are developing and improving the facilities, models, software tools and services offered by Europlanet
Europlanet Project website: http://www.europlanet-ri.eu/
Europlanet Outreach/Media website: http://www.europlanet-eu.org/

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