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Posted by: jasedm Nov 6 2006, 11:42 AM

On September 9th 2004, Nasa announced the possible discovery of two new Saturnian moons, spotted by Carl Murray, from pictures taken just prior to Cassini orbit insertion. Both appear to orbit within 1000 kilometres of the F-ring. In the intervening two years, as far as I'm aware, there have been no follow-up press releases on these possible objects. Does anybody have any subsequent information on these? Possibly (as stated in the release) they were just short-lived agglomerations of ring material, although diameters were quoted as being in the region of 4-5 km

Posted by: pat Nov 7 2006, 11:05 AM

QUOTE (jasedm @ Nov 6 2006, 11:42 AM)

On September 9th 2004, Nasa announced the possible discovery of two new Saturnian moons, spotted by Carl Murray, from pictures taken just prior to Cassini orbit insertion. Both appear to orbit within 1000 kilometres of the F-ring. In the intervening two years, as far as I'm aware, there have been no follow-up press releases on these possible objects. Does anybody have any subsequent information on these? Possibly (as stated in the release) they were just short-lived agglomerations of ring material, although diameters were quoted as being in the region of 4-5 km

There have been no new press releases about these or indeed any new F ring bodies since S/2004 S 6. The ISS team appears to have decided to stop anouncing satellite candidates in the F ring region presumably until they are reasonably sure that they are long lived objects and are reliably able to track them and predict their positions.

Posted by: jasedm Nov 7 2006, 09:56 PM

Thanks Pat - what you say makes sense. It's obviously a lot harder to track objects washed in the 'glare' of the rings than, say Methone, Pallene or Polydeuces (all a comparable size to that estimated for the F-ring candidates) which have all been pretty accurately orbit-determined now. Also I suppose that to be close enough means near periapsis, when demand is highest on the instruments and time is shortest.
There seems to be so much dynamism between the orbits of Prometheus and Pandora, I wouldn't be surprised (allowing for at least two more sizeable moonlets) if there's another example of Janus/Epimetheus orbit swapping going on in there, not to mention other orbital complications connected with the F-ring itself.
I'd love to see (towards the end of an extended mission), some very close observations of this portion of the ring system over a period of a few weeks, aiming to resolve anything down to a hundred metres or so in diameter.

Posted by: jasedm Apr 1 2008, 09:00 PM

Some raw images of the rings taken just prior to periapse have been posted on the Cassini website. I'm aware of the pitfalls of seeing blobs in the raws, and interpreting them as moons, or clumps of material, but this one looks very moonlet-like to me.......

Cosmic ray hit? - this is a similar contrast to the surrounding scene
Fortuitous appearance of background star in the gap? - this batch of images tends to have the background stars slightly smeared
Dust speck on lens? - mmmm...

I've cropped it from http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS39/N00104534.jpg and contrast enhanced slightly

ADMIN CONVERTED JPG ATTACHED

Posted by: jasedm Apr 17 2008, 05:27 PM

No dissent here, so I'm presuming I'm not imagining this - trouble is there was (I think) just the one frame, so it's almost impossible to confirm.
I'm still convinced that rubble is responsible for clearing out most of the observed gaps rather than gravitational resonances.

Posted by: ngunn Apr 17 2008, 07:26 PM

I couldn't (can't) get your attached image to open. Maybe no dissent means others couldn't either. I think I see what you mean in the uncropped original you linked to but I'm not sure.

Posted by: Bill Harris Apr 17 2008, 09:01 PM

The image file has the incorrect extension. It's named snowball.jpeg when the filetype is a .psd .

--Bill

Posted by: jasedm Apr 18 2008, 08:03 PM

Thanks admin for fixing the file extension - the cropped image shows this much more clearly.
It appears that the widest gap in the original image is the Huygens gap (with a small embedded ringlet), and the smaller gaps are exterior to this, at about 120,000km from Saturn's centre. This is obviously well inside the Roche limit - I wonder how far the tensile strength of ice would prevent tidal disruption?

Posted by: tallbear Apr 18 2008, 08:17 PM

QUOTE (jasedm @ Apr 18 2008, 01:03 PM)

Thanks admin for fixing the file extension - the cropped image shows this much more clearly.
It appears that the widest gap in the original image is the Huygens gap (with a small embedded ringlet), and the smaller gaps are exterior to this, at about 120,000km from Saturn's centre. This is obviously well inside the Roche limit - I wonder how far the tensile strength of ice would prevent tidal disruption?

before you all get way too excited......It's a star.....
just about perfectly placed.... but that's what it is.....

T

Posted by: jasedm Apr 18 2008, 08:40 PM

Quel dommage! - totally agree Tallbear that is near-perfect placement in the gap - must have caused a little ripple of excitement over at Ciclops though...
Oh well, back to the drawing board.....

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