[X] My Assistant

[dilo]

Most recent narrow-field images of Enceladus, reported in the "raw images"section of Cassini homepage, are very interesting but also pretty strange...
Images link are reported below and were taken on February 17 using the CL1 and CL2 with increasing exposure time.

http://saturn.jpl.nasa.gov/multimedia/imag...eiImageID=32337
http://saturn.jpl.nasa.gov/multimedia/imag...eiImageID=32338
filtershttp://saturn.jpl.nasa.gov/multimedia/images/raw/raw-images-details.cfm?feiImageID=32339

Looking in particular to first one, sky is bright while Enceladus darkside still black. Apparently, the only possible explaination is that background is the dark side of Saturn atmosphere, but the presence of a star trail below the satellite demonstrate that, incredibly, background is the sky (see first attached image, which is the sun the 3 images associated with RGB channels). I don't know encounter geometry and I will appreciate very much if anyone can help me...
Anyway, the interesting thing is the bright halo near the bottom of Enceladus, clearly showed in the second attached image (an elaboration made strating from first and last image). Could this be the plume produced by some geologic activity (like an iceberg/volcano)?
Regards...

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[dilo]

I used space simulator (http://space.jpl.nasa.gov/) in order to reproduce the geometry of the scene (see attached). Based on the apparent size of Enceladus (near 5.5’, knowing the size of narrow field cam = 21’), image was taken about 12.15UTC, almost 9 hours after the flyby; simulated illumination from Sun and Saturn are consistent with image (phase angles of 153 and 157deg respectively) and the only possible explaination for the sky birightness is the presence of E-ring material, mostly located behind Enceladus (which is darker).
These conclusions are supported by informations reported in the final part of following article:
http://www.newscientist.com/article.ns?id=dn7029
Here is made also clear mention of “ice geysers” as probable cause of continuous surface changes. These ice crystal partially escape the weak gravity, forming the planet's tenuous E ring, as suggested by scientists. “They are looking out for volcanic plumes on the moon's horizon, where they would be easiest to spot against the inky blackness of space”. This is exactly what observed!

PS: Please, can someone explain me how to include an image directly inside the message post, instead to use attachments? Thanks…

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