June 12 2007 Icy Moons (rev 46) |
June 12 2007 Icy Moons (rev 46) |
Jun 6 2007, 07:35 AM
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Senior Member Group: Members Posts: 1887 Joined: 20-November 04 From: Iowa Member No.: 110 |
Rev 46 description available at CICLOPS
http://ciclops.org/view.php?id=3245 Some highlights: Cassini will observe Mimas, the innermost of the mid-sized icy satellites of Saturn June 12, Cassini makes one of its closest passes of the small, inner satellite Atlas, at a distance of only 38,000 km (24,000 mi). With an average diameter of only 31 km (19 mi), Atlas is one of the smallest moons of Saturn. Atlas will only appear to be 120 pixels across (at the equator). However, these images may still provide important clues about the formation of one of the most distinguishing aspects of the tiny satellite: its equatorial bulge. The bulge is thought to have been created by material from Saturn’s A ring being deposited preferentially along the equator of the satellite. A number of observations are dedicated to observing some of Saturn's small moons, in order to refine scientists' estimates of their orbital paths. These sequences include observations of some of Saturn's outer satellites, such as Paaliaq, Hati, and S/2004 S13 I've seen a few of these small outer moons listed recently on the raw image page. They search tool only shows them from the last few orbits. Is this something new they are doing or have they been previously listed as Sky? |
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Jun 7 2007, 07:01 PM
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Member Group: Members Posts: 655 Joined: 22-January 06 Member No.: 655 |
I think it's a recent decision to attempt to pin down the orbital dynamics of some of the newly discovered moons. To my knowledge the mission so far hasn't included any observations of these captured rocks. But out at apoapsis, it strikes me as a good use of the spacecraft's time.
It's a shame no observations are planned on this orbit of Prometheus - the only named moon so far not imaged appreciably better than Voyager managed. I believe the spacecraft comes within 65,000km of Prometheus on June 12th - evidently better opportunities are available later on (including a sub 50,000km pass on June 28th this year). |
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Jun 7 2007, 07:13 PM
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Senior Member Group: Moderator Posts: 3233 Joined: 11-February 04 From: Tucson, AZ Member No.: 23 |
Sorry, no dice AFAIK for Prometheus. The June 12 encounter unfortunately occurs at the same time as the Atlas encounter, and the Rocks/Rings folks chose to image Atlas. The June 28 encounter occurs a very high phase angle. Can't check to see if observations are still planned, but at C/A, you would only see a thin crescent.
EDIT: LOL, I found another good reason why there is no imaging during June 12 encounter: Prometheus is in eclipse at the time. -------------------- &@^^!% Jim! I'm a geologist, not a physicist!
The Gish Bar Times - A Blog all about Jupiter's Moon Io |
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Jun 7 2007, 08:09 PM
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#4
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Member Group: Members Posts: 655 Joined: 22-January 06 Member No.: 655 |
Right decision I think to go for Atlas on this orbit VP, if that was the choice. There's only one closer pass to Atlas (including the EM), but many more opportunities for imaging Prometheus close up and at a decent phase angle.
Must be a difficult job being a mission planner sometimes!! |
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Jun 13 2007, 09:19 AM
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#5
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Senior Member Group: Members Posts: 1276 Joined: 25-November 04 Member No.: 114 |
Some distant looks at Mimas. http://saturn1.jpl.nasa.gov/multimedia/ima...0&storedQ=0
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Jun 13 2007, 09:36 AM
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Senior Member Group: Members Posts: 3648 Joined: 1-October 05 From: Croatia Member No.: 523 |
Atlas images are in. It doesn't look very saucer-shaped in this geometry.
http://saturn1.jpl.nasa.gov/multimedia/ima...iImageID=113545 Pretty noisy, too. -------------------- |
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Jun 13 2007, 10:07 AM
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Member Group: Members Posts: 241 Joined: 16-May 06 From: Geneva, Switzerland Member No.: 773 |
Amazing !!
The surface is so smooth. Only few craters might be seen near the terminator. It seems completely covered by "ring snow". And where is the equatorial ridge ? Marc. |
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Jun 13 2007, 10:46 AM
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#8
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Senior Member Group: Members Posts: 3516 Joined: 4-November 05 From: North Wales Member No.: 542 |
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Jun 13 2007, 12:16 PM
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Junior Member Group: Members Posts: 76 Joined: 19-October 05 Member No.: 532 |
...A number of observations are dedicated to observing some of Saturn's small moons, in order to refine scientists' estimates of their orbital paths. These sequences include observations of some of Saturn's outer satellites, such as Paaliaq, Hati, and S/2004 S13 I've seen a few of these small outer moons listed recently on the raw image page. They search tool only shows them from the last few orbits. Is this something new they are doing or have they been previously listed as Sky? The outer irregulars have been imaged before and yes the target was listed as 'SKY' meaning that the target was a RA/dec coordinate. One of the German group on the Imaging Team has recently begun observing the outer irregulars to get photometry, rotation curves etc and the observation designs for these are specifically targetted to the satellite of interest hence the name appearing as the target. I think that the Cassini observation design software may have only recently been updated to accept the outer irregulars by name as valid targets. |
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Jun 13 2007, 12:26 PM
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#10
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Junior Member Group: Members Posts: 76 Joined: 19-October 05 Member No.: 532 |
Presumably around the perimeter of that image. Looking at these images it may be that it isn't an equatorial ridge at all but that Atlas is pear shaped with bulges at the equator at roughly the sub-Saturn point and 180 degrees from the sub-Saturn point (anti-Saturn point?). The geometry in the latest images has us looking almost straight 'down' onto the 'bulge' facing away from Saturn. It reminds me of satellite imagery looking down on a mountain. Possibly the 'bulge' is cone shaped. So maybe Atlas is roughly spherical with two large cones stuck on pointing towards and away from Saturn. |
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Jun 13 2007, 03:06 PM
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Senior Member Group: Moderator Posts: 3233 Joined: 11-February 04 From: Tucson, AZ Member No.: 23 |
We are looking down on the southern hemisphere of Atlas. The equatorial bulge is the smooth periphery of the image. The south pole is within the rougher bump seen at the center of the disk.
-------------------- &@^^!% Jim! I'm a geologist, not a physicist!
The Gish Bar Times - A Blog all about Jupiter's Moon Io |
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Jun 13 2007, 03:33 PM
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#12
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Junior Member Group: Members Posts: 76 Joined: 19-October 05 Member No.: 532 |
We are looking down on the southern hemisphere of Atlas. The equatorial bulge is the smooth periphery of the image. The south pole is within the rougher bump seen at the center of the disk. Yep, I typed before I'd actually done some work on the geometry. Volcanopele is right, we're pretty much looking down on the south pole so the images are entirely consistent with an equatorial bulge of newer, smoother material ontop an older more eroded ellipsoid. The 'saucer' is back and the 'lemon' out the window. Ah well, it was nice while it lasted. |
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Jun 13 2007, 03:37 PM
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Member Group: Members Posts: 241 Joined: 16-May 06 From: Geneva, Switzerland Member No.: 773 |
OK, thanks. Now I see the perspective.
We can imagine that the actual moon corresponds to the rough core, and the smooth belt to catched ring particules. Marc. |
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Jun 13 2007, 04:09 PM
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Lord Of The Uranian Rings Group: Members Posts: 798 Joined: 18-July 05 From: Plymouth, UK Member No.: 437 |
Here's a version of the picture created from several stacked images. The noise has been removed from each indivdual layer:
-------------------- |
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Jun 13 2007, 04:41 PM
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Administrator Group: Admin Posts: 5172 Joined: 4-August 05 From: Pasadena, CA, USA, Earth Member No.: 454 |
Why is there so much noise in the images -- is it just because we're real close to Saturn and there's lots of charged particles flying around?
I checked the tour page and it appears that periapsis this time around was at 2.7 Saturn radii. We haven't been this close to Saturn since Rev 14 (there was a nice Pandora flyby then, and I note those images were also noisy). --Emily -------------------- My website - My Patreon - @elakdawalla on Twitter - Please support unmannedspaceflight.com by donating here.
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