Friday, March 7, 2008

"Dust halo" or "ring" found around Saturn's moon Rhea?

There has nothing been seen by any camera on Cassini, so the evidence is all indirect yet intriguing: a paper in today's Science (319, 1380-4) talks about "solid material that can absorb magnetospheric particles" which "Rhea's magnetospheric interaction region, rather than being exclusively induced by sputtered gas and its products, likely contains". The evidence for that is the finding that "energetic electrons are depleted in the moon's vicinity" in combination with the "absence of a substantial exosphere" which one would have expected. But what's the absorber? "Combined observations from several instruments suggest that this material is in the form of grains and boulders up to several decimetres in size and orbits Rhea as an equatorial debris disk," continues the abstract: "Within this disk may reside denser, discrete rings or arcs of material." For the JPL (and the media) these possible rings are worth a headline, the LANL goes with the "dusty halo" from the paper's original title instead.

In other news the Large binocular telescope has achieved its first binocular light, taking celestial images using its twin side-by-side, 8.4-meter (27.6 foot) primary mirrors together. • A particularly deep image of Holmes at the CA nebula, showing more coma than typical images. • There are now 131 catalogued pieces of USA 193. • One can observe aurorae in daylight from space, using narrow UV filters. • And if you don't like it here: Perhaps there's a hole into another dimension in plain sight ...

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