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Rev 141 - Nov 20-Dec 10, 2010 - Hyperion and Enceladus E12
jasedm
post Nov 22 2010, 02:34 PM
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The latest article has been up a few days, and goodies include a doppler-tracking pass over Enceladus' northern hemisphere, a search for Rhea co-orbitals, and the first reasonable-range imaging of Hyperion for five years.
The article doesn't state whether a different hemisphere will be on view than that imaged during the targeted flyby in '05, but I suppose it would be very unlucky if this was the case.

Images from the Hyperion encounter should be comparable to this:




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Holder of the Tw...
post Nov 22 2010, 03:42 PM
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The rotation of Hyperion is chaotic, so it may not be possible to predict how it will be oriented very far in advance.
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Hungry4info
post Nov 29 2010, 01:17 AM
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Hyperion images are down.
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nprev
post Nov 29 2010, 01:21 AM
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Thank you, Hungry. Always good to see new views of our favorite celestial sponge! tongue.gif

Speaking of new views, has Hyperion's spin state been decisively resolved yet? I remember some buzz a few years back that it may be chaotic, but have heard nothing further for quite some time now.


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Hungry4info
post Nov 29 2010, 01:36 AM
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Any time smile.gif.
Hyperion's rotation axis was found to be chaotic from ground-based photometry after the Voyager encounters. Something to do with Titan being nearby?


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nprev
post Nov 29 2010, 01:45 AM
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Yeah, it does get pretty close to The Big Guy, and that'd do it!

So, Cassini planners aren't completely sure what they're going to see during each of these encounters. Interesting. I wonder if there's any attempt to see if the spin-axis precession might be "stochastic" instead of straight-up chaotic (if you know what I mean) given that we can now resolve & record the relative positions of small-scale surface features during these encounters.


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Hungry4info
post Nov 29 2010, 01:48 AM
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I was wondering the same thing and did some digging earlier and came across this paper, which seemed to rule that out.

The chaotic rotation of Hyperion
QUOTE
As tidal dissipation drives Hyperion's spin toward a nearly synchronous value, Hyperion necessarily enters the large chaotic zone. At this point Hyperion becomes attitude unstable and begins to tumble. Capture from the chaotic state into the synchronous or state is impossible since they are also attitude unstable. The 3/2 state does not exist. Capture into the stable 2 state is possible, but improbable. It is expected that Hyperion will be found tumbling chaotically.


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Phil Stooke
post Nov 29 2010, 02:20 AM
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Hyperion's rotation has also been modelled as a slow long axis rotation with large precession, like the nucleus of Halley's comet and asteroid Toutatis:

Hyperion: Rotation, Shape, and Geology from Voyager Images
Icarus, Volume 117, Issue 1, September 1995, Pages 128-148
P. C. Thomas, G. J. Black and P. D. Nicholson


This would be complex but predictable, not chaotic.

Phil


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tedstryk
post Nov 29 2010, 03:06 AM
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Glad to see Cassini back at work. These images of Hyperion are phenomenal!


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Ian R
post Nov 29 2010, 06:52 AM
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Here's an early morning crack at a GRN/IR/UV colour composite:

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JohnVV
post Nov 29 2010, 08:49 AM
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it is looking like i am going to need to add some new images to my map of Hyperion
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john_s
post Nov 29 2010, 03:10 PM
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QUOTE (Phil Stooke @ Nov 29 2010, 02:20 AM) *
...This would be complex but predictable, not chaotic.


The latest analysis of Hyperion's rotation was presented at the 2010 DPS meeting in October. The precession of the spin axis is not behaving as expected, perhaps due to internal inhomogeneities. So we still don't have a good rotational model for Hyperion. And to nit-pick, there isn't a clear distinction between "predictable" and "chaotic" - "chaotic" behavior is always predictable in theory, given perfect knowledge of initial conditions- it's just that tiny changes in initial conditions translate to large variations in future behavior.

[edit] I should add that it's my understanding that for Hyperion the rate at which its rotation would diverge from predictions (if we had a good enough understanding of its current behavior to make predictions) is fairly slow (many months?), so while it's truly chaotic it's less chaotic than many other systems, such as the Earth's weather.

John
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Phil Stooke
post Nov 29 2010, 08:36 PM
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Thanks - I hadn't seen that abstract.

Phil


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ugordan
post Nov 29 2010, 08:38 PM
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Looks like the remaining Hyperion images have been dumped onto the raw pages.


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ZLD
post Nov 29 2010, 09:14 PM
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Did a little bit of processing on some of the new data and came up with this:

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This is a false color image using the IR1, GRN and UV3 filters.


Also, it looks like a few images of Titan were actually snapped. A good range of filters were used including Red, GRN, BL1. After a little processing it produced this:

Attached Image


I'm sure someone can do better than this with the data. These were done in a really short time (less than 20m). It looks like a great flyby movie could be done of Hyperion as well.
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