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Posted by: jasedm Aug 29 2006, 09:06 PM

Great orbit coming up.......
Titan on 7th September, followed on the 9th, by Enceladus from ~ 40,000km (not a great phase angle though) Any coverage will overlap that of the best Voyager 2 mosaic (Sarandib Planitia etc) but in much better detail.
Also, Cassini passes less than 12,000km from Methone later on that day (closest approach in the whole mission) - really hope the mission planners managed to retarget some frames to image the little blighter on this orbit.

Can't wait!!

Posted by: volcanopele Aug 29 2006, 09:24 PM

The Enceladus opportunity looks really nice, a nice high phase view over the trailing hemisphere. In terms of mapping, this won't really cover anything we haven't seen before, though the few extra degrees of latitude the sub-solar point has increased by since last March may help.

Unfortunately, we will miss Methone. Not all that surprising considering the dinky size of Methone and the tight scheduling around periapse for Cassini.

Posted by: jasedm Aug 29 2006, 09:50 PM

Shame about Methone - Cassini barrels past just a couple of Titan-diameters away.
Still, another opportunity comes up next June I believe to capture some pics of her at a similar range.

Posted by: volcanopele Aug 29 2006, 09:52 PM

Do you happen to know the phase angle of that encounter? Such an encounter would be best for shape determination. Even at 15,000 km, Methone would only be about 33 pixels across.

Posted by: jasedm Aug 29 2006, 10:01 PM

Phase angle will be 115 degrees, and the range 12,646km on the 27th June next year.

Posted by: volcanopele Aug 29 2006, 10:13 PM

hmm... at that distance Methone would be ~40 pixels across, assuming a diameter of 3 km. it might still be worth it, despite the phase angle. Not sure what the Saturn-shine potential would be (remember the recent Helene images that were high phase, but would help with shape modeling due to saturn-shine.

Posted by: Big_Gazza Aug 30 2006, 01:00 PM

Jason,

Will this encounter be favourable to dark-side imaging courtesy of Saturn-shine? If so, it seems that a good chunk of poorly-imaged terrain would be imaged. The Dione encounter last rev was a good one for Saturn-shine, although no new coverage was obtained.

Generally speaking, do any of the remainder of the primary mission Enceladus encounters provide good coverage of the poorly-imaged region 120 deg to 30 deg longitude? For some reason, this area makes me think of the planet Hoth from The Empire Strikes back...

Cheers,
Gary

Posted by: angel1801 Aug 30 2006, 02:12 PM

On September 25, we will see this poorly imaged area from about 286,000km. For better, wait until 2007 when we get more close looks on September 30, May 27 or June 28. The May 27 and June 28 encounters image this area from about 90,000km.

Posted by: scalbers Sep 7 2006, 06:26 PM

I like the prospects for both Enceladus encouters this month. I wonder exactly what time the image (attached to post #2) is for? From some Celestia animations that I've done I'm wondering if the sub-solar point should be flipped by 180 degrees longitude or something of that nature?

Posted by: volcanopele Sep 7 2006, 07:52 PM

scalbers, the graphic represents the non-targeted encounter on Saturday. The central lat and lon, as well illumination, are based from planning files for the observation (the start of it IIRC). There is some lag time between Cassini C/A and the start of the observation. We don't start taking images until we are about 60,000 km from Enceladus, outbound. That might account for the differences you note.

Big_Gazza, Saturn-shine is definitely in the cards for the observation, but whether it will be any better than what we got on Rev11, covering about the same area, I'm not sure. Unlike the Dione images from last month, the exposure times aren't set specifically to get good saturn-shine observations, unfortunately, similar to the stuff we got in Rev11, where the Saturn-shine contrast wasn't very good. We will just have to see.

angel1801, no ISS observations are planned for the Sept. 25 NT encounter.

Posted by: volcanopele Sep 10 2006, 07:21 AM

Some interesting new images just came down. Enceladus (and Rhea, I think) images come down tomorrow evening. Included in tonight's downlink:

Daphnis and the wakes it leaves on the edges of the Keeler Gap. Not a Rings person, but even I find that impressive!!:
http://saturn.jpl.nasa.gov/multimedia/images/raw/raw-images-details.cfm?feiImageID=82561

A Couple of ringlets in the Encke Gap:
http://saturn.jpl.nasa.gov/multimedia/images/raw/raw-images-details.cfm?feiImageID=82562

Full Iapetus:
http://saturn.jpl.nasa.gov/multimedia/images/raw/raw-images-details.cfm?feiImageID=82504

Opnav Rhea:
http://saturn.jpl.nasa.gov/multimedia/images/raw/raw-images-details.cfm?feiImageID=82345

Cresent view of Mimas (and Herschel crater):
http://saturn.jpl.nasa.gov/multimedia/images/raw/raw-images-details.cfm?feiImageID=82344

Dione (Dido crater very prominent):
http://saturn.jpl.nasa.gov/multimedia/images/raw/raw-images-details.cfm?feiImageID=82343

Leading hemisphere Enceladus:
http://saturn.jpl.nasa.gov/multimedia/images/raw/raw-images-details.cfm?feiImageID=82346
http://saturn.jpl.nasa.gov/multimedia/images/raw/raw-images-details.cfm?feiImageID=82342

Aldebaran behind rings (shadow of Saturn at bottom):
http://saturn.jpl.nasa.gov/multimedia/images/raw/raw-images-details.cfm?feiImageID=82602

Posted by: Myran Sep 10 2006, 07:51 AM

Well thank you fo rthe heads up volcanopele. And yes those waves after Daphnis are easily seen, are the waves on the inner side of the ring the direction this moonlet are heading and on the outside on the trailing side?

Or should I say.....'Remember guys that you get the news here first.' Well its not unusual that we do!

Posted by: Phil Stooke Sep 10 2006, 02:17 PM

On the inner side, the particles ahead of the moon are a-shakin', because they are moving faster, overtaking, and set dancing by the moon as they pass it.

On the outer side, the particles behind the moon are dancing because they move slower than the moon. As the little moon overtakes them they are set moving in and out, while the particles ahead of the moon have not yet been affected.

Phil

PS I edited this... when I first wrote it I said it the other way round. I forgot we are looking at the iluminated south side of the rings, and particles are moving clockwise (top to bottom here).

Posted by: Myran Sep 10 2006, 09:48 PM

Thank you for the correction Phil.....

Edit: No correction needed. Perhaps what I said wasnt entirely clear.

(Edited since my post would just cause confusion if left unaltered)

Posted by: volcanopele Sep 11 2006, 03:28 AM

Here be the Enceladus images:

View over the northern trailing hemisphere:
http://saturn.jpl.nasa.gov/multimedia/images/raw/raw-images-details.cfm?feiImageID=82705

Full-disk view of Enceladus:
http://saturn.jpl.nasa.gov/multimedia/images/raw/raw-images-details.cfm?feiImageID=82731

Tethys:
http://saturn.jpl.nasa.gov/multimedia/images/raw/raw-images-details.cfm?feiImageID=82716

Posted by: Ian R Sep 11 2006, 02:47 PM

I'm sure that this view would make a nice comparison to the Voyager 2 imagery:

Ian.

Posted by: angel1801 Sep 11 2006, 03:25 PM

I have observed that the image of Tethys contained in http://saturn.jpl.nasa.gov/multimedia/imag...eiImageID=82716 is virtually the same as a Tethys shot taken on October 28, 2004 from an almost same distance but with a little more latitude.

Posted by: jasedm Mar 11 2008, 09:46 AM

Not sure where to post this, so have plumped for this thread as it mentions shape-determination issues for Methone.
A few interesting images of this tiny moon have just been posted on the raw images pages, but they are more than just basic opnavs, as it appears that the moon's orbit has now been determined sufficiently-well to allow the frames to be fairly long exposure ones, tracking the moon in it's orbit, and consequently show a discernible disc.
Does anybody know the exposure times, distance from the moon (9th March was the date quoted, so distance must be in the region of 1.2million km), and Methone's diameter (I've seen figures varying from 1.6km to 4km quoted)
The frames are http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS38/N00103667.jpg,and http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS38/N00103655.jpg
Maybe the range is still too distant, but it appears on this evidence that Methone is at least roughly spherical.

Posted by: ugordan Mar 11 2008, 10:45 AM

I don't think you can say that with much confidence when looking at the two images. The moon was obviously unresolved and the circular impression you get is the camera's point spread function at work. It looks like Methone was overexposed in the images as well.