Cassini Celebrates 10 Years in Space

The Cassini team is reveling in the outpouring of public praise for the mission.  Launched on October 15, 1997, Cassini-Huygens has spent ten years in space and is over three fourths the way through its prime mission, to explore the Saturn system, its rings, moons, magnetic field and the large moon Titan (see ESA and NASA).
    Scientific discoveries continue to pour in.  Unless the spacecraft fails or funding is cut off, there is no end in sight for one of the most successful outer planet missions in history.  The Cassini Imaging Team has posted a gallery of recent hi-res color images at Ciclops.org.  One picture in particular seems suitable for the occasion: a dazzling rainbow on the rings caused by the “opposition effect” of sun glint on icy ring particles (also posted by JPL).
    Several recent discoveries were reported in the literature:

1. Tropical Titan:  the University of Chicago described Titan as a tropical moon – in its own way.  Despite the -290 degree chill, Titan has an atmosphere saturated with methane that acts like the humidifier and moisturizer for this bizarre world.  At that temperature, in fact, methane is even more volatile than water is on Earth.  EurekAlert even gave the weather forecast: “Morning forecast on Titan calls for widespread methane drizzle off Xanadu.”  See also another EurekAlert article that says the European Southern Observatory shares credit for this discovery.
2. Southern Lakes:  The latest radar swath taken by Cassini across Titan’s southern latitudes revealed some lakes there, too – but fewer, apparently, because it is summertime in the south.  If the mission continues for several more years, scientists are eager to see if the southern lakes grow and the northern lakes dry up as summer shifts northward.  See the JPL press release for a montage of the northern lakes and a shot of the southern lake; see also European Space Agency.
3. Runaway Iapetus:  Preliminary explanations for the black-and-white case of Iapetus are starting to come in after last month’s close flyby (see 09/13/2007).  Some scientists think, according to a JPL press release, that solar heating leads to a process called thermal segregation.  The water ice in the more-absorbent dark material sublimates and re-deposits on the cold white parts – a runaway and irreversible effect.  This may explain why dark material tends to puddle in the bottoms of craters or hang on crater walls facing the equator.  They believe the dark material is only about a foot deep.  Whatever the explanation, the amazing images of Iapetus from the September 10 flyby are sure to occupy scientists for years to come.
4. The Ancient Mountains of Iapetus:  Because the mysterious mountain ridge on Iapetus is heavily cratered, scientists assume it is ancient.  They are ruling out theories that a ring collapsed onto the surface, because it would not explain apparent tectonic features associated with the ridge.  See the JPL press release.
5. Jet Blue:  A lovely limb shot of Enceladus with its geyser plumes colored blue was released in another JPL press release.  Imaging team scientists Jason Spitale and Carolyn Porco were able to line up the plumes with the tiger stripes.  Their results, published in Nature last week,¹ suggest that more hot spots will be found in future flybys.
   

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   1.  Spitale and Porco, “Association of the jets of Enceladus with the warmest regions on its south-polar fractures,” Nature 449, 695-697 (11 October 2007) | doi:10.1038/nature06217.

Like Jupiter (10/15/2007), Saturn was filled with surprises.  Nothing in the Saturn system requires billions of years; many things require mere thousands.  A lot of needless cerebral horsepower is expended trying to keep apparently young phenomena going for unnecessary eons.  We can enjoy the show without the mythology.