March 28, 2007 | David F. Coppedge

Saturn Still Serving Surprises

The Cassini Spacecraft, three-fourths of the way into its 4-year prime mission, is not running out of new things to see.  Some of the latest discoveries are both awesome and strange.

  1. A Hex on the Pole:  As if the south pole of Saturn, with its earth-sized hurricane (picture) were not dramatic enough, the north pole seems determined to steal the thunder.  A bizarre hexagon-shaped feature was observed surrounding the pole that has scientists scratching their heads.  The press release at Jet Propulsion Laboratory (JPL) states that the structure, unique in the solar system, is a long-lived feature.  It’s not just a shallow cloud formation, either; the hexagonal shape extends 60 miles deep into the atmosphere.  How such a shape could form and endure in a fluid is a new and unexpected puzzle to solve.  Watch this short video of the hexagon in motion.
  2. The whole Enceladus:  Little Enceladus, the second sizeable moon beyond the rings, is like a planetary David tugging on Goliath’s beard.  This little moon, no bigger than the British Isles, amazed scientists when its south polar geysers were caught in action in 2005 (see 02/10/2007, 11/28/2005).  Now, scientists have found that this tiny erupting moon is influencing Saturn’s gigantic magnetic field.  It spurts out so many charged particles, it drags the plasma with it, causing slippage of the plasma disk.  The JPL press release explains, “In a David and Goliath story of Saturnian proportions, the little moon Enceladus is weighing down giant Saturn’s magnetic field so much that the field is rotating slower than the planet.”  As a result, this throws off measurements of the rotation rate of the magnetic field, a key parameter used to infer the planet’s inner rotation rate.  See also the Science Daily report.
        Little Enceladus made yesterday’s Astronomy Picture of the Day.  The output of the moon’s geysers are clearly seen feeding the E-ring around Saturn.  One wonders whether this is an unusual burst of activity, or a long-lived feature – and how long such a feature could live.  See our previous story from 03/13/2007.
  3. Tug of Warp:  Little moons around the F-ring of Saturn tug at the material in noticeable ways.  JPL issued this picture of Prometheus dragging material out of the ring, and breakaway clumps of material from previous passages of nearby moons.  The material may pass hands back and forth between the moons and the rings, but scientists are not sure; some of the embedded moonlets appear to have eccentric orbits and pass right through the F-ring at times.
  4. Missing pockmarks: wondered where all the craters went on Titan.  Cassini’s radar mapper has only examined about 10% of Titan’s surface, but only four clear craters have turned up – a “surprisingly small number” for a moon nearly the size of Mercury.  Either the craters are quickly erased or the surface is young.  “If Titan’s surface had the same density of craters that other Saturnian moons have, there should be thousands of craters,” remarked one member of the science team.
  5. Charming physics:  For those liking to delve deeper into the physics of Saturn, a new CHARM PDF file (Cassini-Huygens Analysis and Results of the Mission) was posted 3/27.  Dr. Claudia Alexander delivered a colorful Powerpoint presentation about science results from the magnetic field observations.  Click here for a list of previous CHARM presentations on other aspects of the Saturn system.  To see Dr. Alexander in action, click here for her latest videocast on mission status, and here for the archives.

To add to Cassini’s art gallery, a beautiful color picture of Saturn was taken with the large moon Rhea.  The Imaging Team has their own website with special features, like Saturn Golf, and the Planetary Society keeps a running blog of happenings.  Since 18 countries are involved in the mission, you can find additional Cassini-Huygens stories from a European perspective at the European Space Agency.  Even amateur scientists (and some pros with aliases) gather at the Unmanned Spaceflight forum to share their reactions and opinions.  Some even take the raw images and do amazing things with them, like this and this.  Anyone with imaging tools and some imagination can join the fun.  Our previous Cassini story was on 03/01/2007.
    Cassini is flying by Titan numerous times this year and next (see schedule), looking for more lakes and evidences of cryovolcanism, studying the atmosphere and mapping the surface with radar.  Some other big-news encounters are in the plans.  June 27 Cassini flies by Tethys at close range for the second time.  On August 30 there is a close flyby of Rhea.  On September 7, one of the most spectacular and waited-for moon encounters of the mission occurs: a flyby of Iapetus from only 932 miles (see latest image and 01/07/2005 story).  And, to top it all, next March 12 the spacecraft will attempt a daring plunge through the geyser plume of Enceladus from only 14 miles up –the closest encounter of the tour.  This will enable the instruments to collect samples of the material, precious data that will help scientists understand the processes at work in the smallest hyperactive globe in the solar system.  The prime tour ends with a “high dive” high-inclination sequence (August 31 to July 1) that should provide stunning views of the rings and the polar hexagon from above.
    The end of the prime mission (July 2008) may not be the grand finale; assuming Congress approves plans for an Extended Mission, and the spacecraft stays healthy, Cassini has enough fuel and power to continue to dazzle us with its Saturn postcards for two or three years – or more.

An amazing story.  Enjoy it while you can: a ringside seat on the most successful interplanetary tour ever.  It won’t feel the same when Cassini is in the history books; it’s much more fun to learn while it is happening.  Go Cassini!  Keep those bits coming, and fill our dishes with wonder.

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Categories: Physics, Solar System

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