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Dawn Survey Orbit Phase, First orbital phase
tasp
post Aug 1 2011, 06:46 PM
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My first thought about the cracks was we are seeing crustal sloughing into the crater hole. (it's big, for sure, but technically, the missing segment of Vesta is a hole) The tensile strength of the materials surrounding the crater would need to be checked for consistency this idea. Also, the segments between the cracks would be subject to compressive effects as the assemblage creeped (oozed? shifted?) downslope. Not sure I see anything that might be like that at this resolution in the images.
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john_s
post Aug 1 2011, 07:34 PM
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QUOTE (siravan @ Aug 1 2011, 12:03 PM) *
In the Enceladus case, change of the axis of rotation can be explained based on polhode phenomenon. But that needs an energy dissipation mechanism, which for Enceladus is based on the tidal lock (as also the possible 'ocean'). But for a free solid body like Vesta, what is the dissipation mechanism?


Large Vesta-sized bodies will settle fairly quickly into stable rotation about the minimum moment of inertia after their rotation is perturbed, due to internal frictional dissipation - tumbling will produce internal stresses that will cause motion along fractures, etc., that will dissipate energy and damp out the tumbling (Burns and Safronov 1973).

John
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t_oner
post Aug 1 2011, 07:54 PM
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Here is a quick smoothing of the rotation clip. I had to compress a lot it due to 1 MB limit.
Attached File(s)
Attached File  vesta_smooth_rotation.avi ( 1008.84K ) Number of downloads: 898
 
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machi
post Aug 1 2011, 08:30 PM
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Excellent!
Beautiful rotation wheel.gif rolleyes.gif


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Phil Stooke
post Aug 1 2011, 08:36 PM
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The color image is up on the photojournal now.

Phil

http://photojournal.jpl.nasa.gov/catalog/PIA14325


PS before getting too carried away with explanations of grooves, let's consider the other grooved bodies - will the explanation work more generally?


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jasedm
post Aug 1 2011, 08:49 PM
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Composed of completely different stuff I know, but it looks remarkably Miranda-esque to me
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antipode
post Aug 1 2011, 09:18 PM
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The crater count looks low over the impact area - I guess that makes sense, what is it - a billion years old?
Seems to be several sites of mass wasting/downslope movement. And those dark areas are fascinating!

Very very rugged, very very cool. Might be a good place for a lightweight instrumented penetrator (if we ever visit again!)!
Although Ceres is the main course, this is a fantastic entree...

P
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ugordan
post Aug 1 2011, 09:22 PM
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QUOTE (Tayfun Íner @ Aug 1 2011, 09:54 PM) *
Here is a quick smoothing of the rotation clip.

Very nice!


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nprev
post Aug 1 2011, 11:23 PM
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Fantastic, Tayfun!!!

Man...there's a LOT of interesting features on this little world!


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elakdawalla
post Aug 1 2011, 11:30 PM
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QUOTE (Explorer1 @ Aug 1 2011, 09:58 AM) *
There will still be PDS releases, right?

It may be a long wait. I asked about this after the press briefing, and Marc thought that the PDS timeline was 6 months....AFTER they leave Vesta. sad.gif

In the meantime, I have now decomposed the high-resolution version of the animation into its component frames. Here you go, guys; have fun.
http://planetary.s3.amazonaws.com/misc/Vesta_rotating.zip
Attached image(s)
Attached Image
 


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volcanopele
post Aug 1 2011, 11:39 PM
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Lol, I got to about frame28 before I noticed your message. Oh well. I will work up a few anaglyphs if and when I find my red-blue glasses. I know it is here somewhere.


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nprev
post Aug 2 2011, 12:40 AM
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Mrs. nprev's comment on the movie:

"Huh. Looks like biscuit. Even has lines around the middle like biscuit!"

laugh.gif, but insightful. The grooves sure look like compressional features to me from the south polar impact.


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MarkG
post Aug 2 2011, 01:04 AM
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What can make a series of long, straight grooves along the equator of an isolated self-gravitating body?
Debris collapse into extension cracks is one possibility. But what would cause straight cracks at the thickest part of the body?
In the South Pole impact, as the debris was blasting away, the center of mass of Vesta became shifted towards its North Pole, and the area around the crater rim became very high ground. The result static force on the equatorial region would have been compressive.
However, the dynamic situation would have been different. In solids, compression waves travel faster than shear waves, and the bulk (2/3) of the momentum transfer (apart from vaporization heating) from the impact would be transferred by the shear waves, especially an angular momentum change.
With Vesta getting its bell rung so hard, the equator could have been the mega null/shear zone between torsional resonance modes. With debris falling on/in/around the cracks and partially filling them, we could end up with the current distribution.
With limited information coming from Dawn, they'll just have to put up with theories from the bleachers (cheap seats for the Brits).
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Phil Stooke
post Aug 2 2011, 01:45 AM
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Despite the Dawn team wanting this to be a very primitive body dating back to the Dawn of the solar system, there's no particular reason why it could not have been larger at a very early date and to have lost a lot of mass though large impacts to become what we see today. I only suggest this to say that the grooves may be explained by events whose records are no longer visible to us. It's like Phobos - everybody wanted the grooves to be the result of Stickney despite the fact they have no geometric relationship to it at all. At least we can lay the old story of Mars ejecta to rest at last!

Phil


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Gladstoner
post Aug 2 2011, 01:58 AM
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Wow. It looks like baling wire is holding the asteroid together.... smile.gif

It never ceases to amaze me how new types of features keep showing up on these newly explored worlds.

Speaking of new features, this little image artifact

[attachment=25052:Vesta_blemish.JPG]

looks a lot like Tsiolkovskiy on the moon:

[attachment=25053:R3440097...vsky_SPL.jpg]
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