Tuesday, June 28, 2005

New Pandora Image: Off Pandora's Shoulder

Continuing the series of small, inner satellite images started yesterday with Janus, CICLOPS has released this view of Pandora. Pandora orbits just outside the F ring. This image was discussed here earlier when it was taken last month. Very few craters are seen in this view, though that could be a result of the relatively low phase angle, as numerous craters were noted in Voyager images of this satellite. This image has a resolution of 2 km/pixel, though it has been magnified 2x to improve feature visibility.


Blogger Bruce Moomaw said...

Interesting abstract from the July "Icarus":

"Rotational dynamics of planetary satellites: A survey of regular and
chaotic behavior

V.V. Kouprianov and I.I. Shevchenko

Pulkovo Observatory of the Russian Academy of Sciences

"The problem of observability of chaotic regimes in the rotation of
planetary satellites is studied. The analysis is based on the inertial and orbital data available for all satellites discovered up to now. The Lyapunov
spectra of the spatial chaotic rotation and the full range of variation of the spin rate are computed numerically by integrating the equations of the
rotational motion; the initial data are taken inside the main chaotic layer near the separatrices of synchronous resonance in phase space. The model of a triaxial satellite in a fixed elliptic orbit is adopted. A short Lyapunov time along with a large range of variation of the spin rate are used as criteria for observability of the chaotic motion. Independently, analysis of
stability of the synchronous state with respect to tilting the axis of
rotation provides a test for the physical opportunity for a satellite to rotate chaotically. Finally, a calculation of the times of despinning due to tidal evolution shows whether a satellite's spin could evolve close to the synchronous state. Apart from Hyperion, already known to rotate chaotically, only Prometheus and Pandora, the 16th and 17th satellites of Saturn, pass
all these four tests."

Have Cassini's photos provided any information yet on the rotation of
Prometheus and Pandora, Jason?

6/29/2005 11:01:00 AM  
Anonymous Phil Stooke said...

I don't know if Jason replied privately to you, Bruce... and bear in mind I don't know anything about what the Cassini teams are up to, but I would be surprised - very surprised - if Cassini had yet made enough observations of these two moons to say anything new about their rotation.

I would also be very surprised indeed if they turned out to be in anything but a very stable synchronous rotation. This close in, and with such elongated shapes (Prometheus especially), braking into synchronous rotation should be quite effective, though admittedly their close passes might excite a bit of libration.

I would expect that a lot of observations sufficient to pin down the orientation of the long axis at different times would be needed to say anything with certainty here. Actually stereo would be really useful, so if I could plan the observations I would try to space out the pics a bit more during these close passes, to get some stereo separation. But this isn't really my area! Just blethering.


6/30/2005 06:47:00 AM  
Blogger Bruce Moomaw said...

Actually, in the case of Prometheus we can probably confirm that -- in every one of several photos I've seen of it from Cassini (and one from Voyager 2), its long axis has indeed been pointing straight toward Saturn. In the case of Pandora, however, the photos I've seen so far have been unclear on the subject.

6/30/2005 03:06:00 PM  
Blogger Jason said...

Unfortunately, I don't really know. I haven't been paying too much attention to the discussions on small satellite rotational dynamics.

7/01/2005 01:01:00 PM  

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