Cassini Shines in the Light of Saturn

Since its arrival at Saturn last June (see 07/01/2004 entry), the Cassini orbiter has achieved a string of phenomenal successes, and these just 15% of the way into its tour of Saturn’s rings, moons and magnetosphere (see JPL press release).  The prize has been publication of initial science results in Nature¹ and Science² – the cover stories in both.  A few of the more surprising and significant results are listed here.  These papers focus on Saturn’s atmosphere and rings, and the moons Phoebe and Iapetus.  We’ll have to wait for official scientific results from the Huygens probe (see 01/21/2005 entry) and the flybys of Titan.

• Aurora varialous:  Saturn’s auroras (picture) show unique spiral structures and persist unusually long.  Unexpectedly, they do not appear intermediate between those on Earth and Jupiter (see EurekAlert for summary).  Saturn’s aurora can brighten by a factor of 4, depending on solar wind activity.  Like the roar of a campfire in the wind, Saturn’s radio emissions increase when the solar wind blows harder (see explanation on EurekAlert).
• Ring spokes (picture) that were discovered by Voyager and detected by Hubble have not yet been seen by Cassini.  Apparently the phenomenon is a function of low sun angle.  If so, it may be a couple of years before Cassini can detect them.
• Ring irregularities:  At closest approach, Cassini was able to get the highest resolution scans across the rings ever taken (pictures).  These show unexplained irregularities in some narrow and broad rings.  Some may be due to non-Keplerian and non-resonance forces, such as shear stresses or undulations caused by meteoroid impacts (picture).
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