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Rev166: May 11th - May 28th 2012, Tethys, Methone, Titan
ugordan
post May 24 2012, 06:11 PM
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I never cared much for the "total distance travelled" number. Isn't it really pretty meaningless when you think about it? What frame of reference was used? Cassini was cruising through the solar system for 7 years so one can assume the trajectory length centered around the Sun was what was measured. What happened when it entered the Saturnian system, did the statistic switch (and at which point?) to measuring the length of all the ellipses centered around the Saturn or still the heliocentric path?

It's also much easier to clock in billions of km if you're in the inner solar system. Speaking of which, how "far" did MESSENGER travel?


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john_s
post May 24 2012, 08:06 PM
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And how far have I travelled, sitting on my butt reading UMSF ? rolleyes.gif

John,
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jasedm
post May 24 2012, 08:53 PM
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QUOTE (ugordan @ May 24 2012, 07:11 PM) *
I never cared much for the "total distance travelled" number. Isn't it really pretty meaningless when you think about it? What frame of reference was used?


Uh ok... sorry.
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ugordan
post May 25 2012, 04:31 PM
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No need to apologize. To each his own.


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Greenish
post May 25 2012, 05:46 PM
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What is the orientation of Methone? Is the long axis pointed towards Saturn (similar to a gravity-gradient stabilized spacecraft)? If this is in fact a loose dust pile, is this the expected type of deformation?

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jasedm
post May 25 2012, 06:03 PM
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QUOTE (ugordan @ May 25 2012, 05:31 PM) *
No need to apologize. To each his own.


Indeed.
Thank you for your forbearance. In future I shall ensure I assiduously check the frames of reference employed, before posting such thoughtless frippery.
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ngunn
post May 25 2012, 09:26 PM
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QUOTE (Greenish @ May 25 2012, 06:46 PM) *
What is the orientation of Methone? Is the long axis pointed towards Saturn (similar to a gravity-gradient stabilized spacecraft)? If this is in fact a loose dust pile, is this the expected type of deformation?


I like replying to a first post because it gives me the chance to say: Helllo and welcome. smile.gif
I don't know the answer to your question, but it's a good question! My first guess is that material is deposited preferentially around the equator as is the case with Atlas so no reorientation is needed for that, in fact it's self-stabilising. That establishes an oblate ellipsoid with one short axis and two long ones. I'm not sure that the recent images imply a significant difference between the two axes in the equatorial plane, so it may not have 'a' long axis.
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volcanopele
post May 25 2012, 10:12 PM
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North is down in the raw images.


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Greenish
post May 26 2012, 04:04 AM
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QUOTE (ngunn @ May 25 2012, 04:26 PM) *
I like replying to a first post because it gives me the chance to say: Helllo and welcome. smile.gif
I don't know the answer to your question, but it's a good question! My first guess is that material is deposited preferentially around the equator as is the case with Atlas so no reorientation is needed for that, in fact it's self-stabilising. That establishes an oblate ellipsoid with one short axis and two long ones. I'm not sure that the recent images imply a significant difference between the two axes in the equatorial plane, so it may not have 'a' long axis.


Heh... I've been lurking a while, didn't realize it was actually my first. Thanks for the welcome. I've learned a lot here!

So Methone is shaped more like a Skittle than a football? That wasn't clear (to my uncalibrated eye) from the images, or comparisons others made to elongated asteroids, and I hadn't seen any actual 3-axis numbers, just a mean radius estimate. But it guess it would be a more expected shape for something that formed there versus being captured. I guess we'll see.
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rlorenz
post May 26 2012, 01:10 PM
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QUOTE (Greenish @ May 25 2012, 11:04 PM) *
So Methone is shaped more like a Skittle than a football?


Hmm. I suggest with an international audience skittle and football are poor words to use as shape descriptors.....

Skittle, upper case, as in the (US) candy means oblate spheroid (one short radius, two long) and could be referred to by the UK sweet named a Smartie (like US M&M ; I'm a big fan of food analogies in planetary science, by the way...)
but a skittle (lower case, UK useage) could refer to a bowling pin - a perhaps bi-lobed prolate spheroid (two short radii, one long)
rather like comet Borelly. So without catching the case of the leading character, it's a bit ambiguous.

And then there is football, which to much of the world means a sphere (or a convex-hulled truncated icosahedron leather approximation of the same) rather than the prolate ellipsoid which you actually mean in US useage..... ;-)

Maybe someone can make a cool montage of confectionery and sports goods, with the aspect ratios and end radii marked up - maybe there are even some 'universal' confections like (originally Italian) Tic-Tac's that are good analogs of planetary bodies...
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rlorenz
post May 26 2012, 01:12 PM
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QUOTE (rlorenz @ May 26 2012, 08:10 AM) *
Hmm. I suggest with an international audience .....


I can't believe I just mis-spelled usage, twice.
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Explorer1
post May 26 2012, 05:03 PM
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I think we would have noticed if Methone was as irregular as a bowling pin (like that dog-bone asteroid, Kleopatra?)

Or we can go with eggs, those are universal, right? wink.gif
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Stu
post May 26 2012, 05:30 PM
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Actually, when you said Skittle' this UK resident thought you were referring to the small, coloured-shell chewy sweet ('candy' in US usage...) wink.gif


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john_s
post May 26 2012, 07:32 PM
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QUOTE (volcanopele @ May 25 2012, 04:12 PM) *
North is down in the raw images.


We've been used to having north "Up" in the images, but now that the sun is north of the ring plane, post-equinox, it's easier to keep the spacecraft radiators in the shade (as they need to be) by flying "upside down". So north "down" will be more common for the rest of the mission.

John
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Greenish
post May 26 2012, 10:50 PM
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Probably not the best descriptors, the geometrical ones are better... compared to other forums this is not a lay audience nor a US-centric one.

To the point though, and not trying to be repetitive - I'd be interested if anyone can tell if it is prolate or oblate.
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