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Posted by: pat May 25 2006, 02:49 PM

Well 44 images from the 2006 May 22 Polydeuces ~64,000 km flyby have hit the JPL raw images site.

e.g. http://saturn.jpl.nasa.gov/multimedia/images/raw/raw-images-details.cfm?feiImageID=76686

It very much looks like the stretching and conversion to JPEG for the images on this site have pretty much killed the original 12 bit images with Polydeuces now appearing to be overexposed. I'm pretty damn sure that the 12 bit VICAR images do NOT have an overexposed Polydeuces.

Posted by: jasedm May 25 2006, 04:35 PM

The range to target wasn't displayed (presumably they're not 100% sure of the orbital dynamics yet) and for a ~13km moon, it appears too small in the frame to have been imaged from ~ 64000km.
From that distance, the resolution should have been better than the calypso coverage, so either it's MUCH smaller than 13km in diameter, or, it was targeted from a much greater range (I'm guessing double that of closest approach)

Posted by: ugordan May 25 2006, 05:00 PM

Oh, they're pretty certain of its orbital dynamics by now. Look how well they nailed its position to the center of the frame. Like most moons, the orbit is probably pretty much circular so they know exactly how far Cassini passed by. The problem is the raw image site doesn't seem to want to display the distances to some (less major?) targets of interest.

Posted by: jasedm May 25 2006, 05:21 PM

Agreed Gordan, the boresight was almost 100% spang-on. It just seems that the only time (except when pointed at UNK or SKY ) that the distance isn't posted is when the target is a moon either confirmed by, or discovered by the Cassini team - that is, Daphnis, Polydeuces, Methone and Pallene. All other targets have ranges down to the last kilometer.

Posted by: pat May 26 2006, 11:44 AM

The 64,000 km distance was quoted by tallbear in the 'May 20 Icy Moon Imaging' thread

"The closest Polydeuces pass in the Prime Mission is on

2006-142T14:53:09.0 64057 km"

There are no publically realeased SPICE kernels for Daphnis, Polydeuces, Methone & Pallene hence the lack of distances for images targetted to these objects on the JPL raw site. Of course there are ephemerides that the Cassini Project is using for these objects that appear to be pretty damn accurate.

As for the size of Polydeuces and that 13 km diameter figure? The value is 3.5 km diameter in Porco et al. 2005. Science 307, 1226-1236. In the images the longest axis of Polydeuces is ~9-10 pixels. 9-10 NAC pixels at 64000 km corresponds to 3.46-3.84 km which is consistent with the Porco et al. value. I'm not sure where that 13 km figure came from. It was quoted by TritonAntares in the afore mentioned 'May 20 Icy Moon Imaging' thread and he possibly got it from the JPL Cassini saturn satellites page at http://saturn.jpl.nasa.gov/science/moons/moonDetails.cfm?pageID=19 . The JPL Saturn satellites page is cleary incorrect as the current definitive paper (for the diameter at least), that Porco et al. one in Science , gives 3.5 km diameter especially since the images agree with the value in the paper. Incidently the current best orbit paper for Polydeuces is Murray et al. 2005. Icarus 179, 222.

Posted by: TritonAntares May 26 2006, 06:01 PM

Hi Pat!

Sorry, I must admit to be the bad guy who posted this false dimension number of 13 km...
I carelessly got this info from the JPL Cassini saturn satellites page.

Nice your cleared this point with your above mentioned papers.
With 3,5 km diameter, Polydeuces will surely show no more than a larger dot at a minimum of 64.000 km.

Bye.