Approaching Iapetus - what makes it two-faced?

vogon13 · Aug 20, 2007

The only thing we will be discussing is how amazingly prescient I have been . . . . <div class="Discussion_UserSignature"> TPTB went to Dallas and all I got was Plucked !!So many people, so few recipes !!Let's clean up this stinkhole !! </div>

vogon13 · Aug 20, 2007

GAG !! <img src="/images/icons/tongue.gif" /> <img src="/images/icons/laugh.gif" /> <div class="Discussion_UserSignature"> TPTB went to Dallas and all I got was Plucked !!So many people, so few recipes !!Let's clean up this stinkhole !! </div>

Smersh · Aug 20, 2007

have this crazy idea that Iapetus is a "siamese twin"! Two moons that have bonded in the dim distant past while they were still in a semi-solid state and colliding at low speed. This would explain the ridge along the equator as well as the differce in appearance of the two halves. Sorry I'm late into this discussion, but in my opinion Iapetus is the most bizarre object in the Solar System, just because of that ridge. It is just as though two halves have been badly welded together and your "crazy idea" is as good an explanation as any I think. I'm really hoping that Cassini can throw some light on the reason for this feature. <div class="Discussion_UserSignature"> <h1 style="margin:0pt;font-size:12px">----------------------------------------------------- </h1>Lady Nancy Astor: "Winston, if you were my husband, I'd poison your tea." Churchill: "Nancy, if you were my wife, I'd drink it."Website / forums </div>

vogon13 · Aug 20, 2007

Well, how about that!! And I'm the only one. {yevaud has a custom jobbie, so for now, mine is unique.} Looks cool. [sniff] [lip quavers] <div class="Discussion_UserSignature"> TPTB went to Dallas and all I got was Plucked !!So many people, so few recipes !!Let's clean up this stinkhole !! </div>

Boris_Badenov · Aug 20, 2007

Congrats are in order!!!<img src="/images/icons/smile.gif" /><img src="/images/icons/smile.gif" /><img src="/images/icons/smile.gif" /> How do you plan to celebrate? Ummm, ahhh, after thinking about that for a moment, I don't think I want to know.<img src="/images/icons/crazy.gif" /> <div class="Discussion_UserSignature"> <div align="center">. </div><div align="center">Never roll in the mud with a pig. You'll both get dirty & the pig likes it.</div> </div>

brellis · Aug 20, 2007

congrats vogon - Local Group - now you have a galaxy for each of the voices in your head! <div class="Discussion_UserSignature"> I'm a recovering optimist - things could be better. </div>

robnissen · Aug 20, 2007

Of course now, you will have to obey your emperor!

3488 · Aug 21, 2007

Vogon IS the emperor!!!!!!!!!!!!!! <img src="/images/icons/laugh.gif" /> Congrats vogon13 to reaching Local Group. <img src="/images/icons/laugh.gif" /> 20 Days to Iapetus & counting. For those wondering why there have been no images from Cassini for the last few days, it is because Cassini & Saturn have been in Solar Conjunction, i.e on the far side of the Sun. Saturn to the upper left of the Sun. Both are in Leo the Lion. I think that bright star immediately to the upper left of the Sun is Regulus / Alpha Leonis. So no worries, there is nothing wrong. Andrew Brown. <div class="Discussion_UserSignature"> "I suddenly noticed an anomaly to the left of Io, just off the rim of that world. It was extremely large with respect to the overall size of Io and crescent shaped. It seemed unbelievable that something that big had not been visible before". Linda Morabito on discovering that the Jupiter moon Io was volcanically active. Friday 9th March 1979.http://www.launchphotography.com/ http://anthmartian.googlepages.com/thisislandearthhttp://web.me.com/meridianijournal </div>

MeteorWayne · Aug 21, 2007

Need to clarify that a bit. The brightest object in the scene is Mercury. Saturn is the one to the upper left of the sun. To the left of the sun is Regulus (alpha Leonis) If you go here you can select the full resolution (35MB) or 1/4 resolution (8MB) movie of the last week or so. Mercury is the bright object moving right to left. (Mag -1.4, 6 times s bright as Saturn) Both Regulus (Mag +1.4 )and Saturn (mag +0.6) are moving left to right, with Saturn leading. <div class="Discussion_UserSignature"> But the Krell forgot one thing John. Monsters. Monsters from the Id. I really, really, really, really miss the "first unread post" function </div>

3488 · Aug 21, 2007

Sorry MeteorWayne, I did suspect that bright spot might have been Mercury, but looked too close. The scale of the image threw me a bit. Thanks for clarifying that MeteorWayne. ------------------------------------------------------------------------------------------------- Anyway an update on Iapetus from the NASA / JPL Planetary Photojournal. Original Caption Released with Image: As the Cassini spacecraft sets up for its September 2007 close encounter with the two-toned moon Iapetus, the spacecraft is seeing more of the moon's bright, trailing hemisphere. This is a region Cassini has seen relatively little of until recently. The September encounter will provide high resolution images of this region, including the large crater seen here at about the five o'clock position. North on Iapetus (1,468 kilometers, or 912 miles across) is up and rotated about 5 degrees to the right. The image was taken using a spectral filter sensitive to wavelengths of ultraviolet light centered at 338 nanometers. The view was acquired with the Cassini spacecraft narrow-angle camera on July 3, 2007. The view was acquired at a distance of approximately 2.2 million kilometers (1.4 million miles) from Iapetus and at a Sun-Iapetus-spacecraft, or phase, angle of 53 degrees. Image scale is 13 kilometers (8 miles) per pixel. The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo. For more information about the Cassini-Huygens mission visit <div class="Discussion_UserSignature"> "I suddenly noticed an anomaly to the left of Io, just off the rim of that world. It was extremely large with respect to the overall size of Io and crescent shaped. It seemed unbelievable that something that big had not been visible before". Linda Morabito on discovering that the Jupiter moon Io was volcanically active. Friday 9th March 1979.http://www.launchphotography.com/ http://anthmartian.googlepages.com/thisislandearthhttp://web.me.com/meridianijournal </div>

h2ouniverse · Aug 21, 2007

Hi Andrew and all, Andrew you asked for my bet: I am still betting on the collapsed ring scenario. I would personnally prefer any scenario involving big crack and upsurge of liquid water, but not very likely given the aspect of the moon (no other crack visible). Also the fact that it is just on a half and on the leading hemisphere tends to rule out internal contraints. But we will see. I doubt btw that the fly-by will be enough to solve the mystery. Best regards.

h2ouniverse · Aug 21, 2007

In reply to "Iapetus is the most bizarre object in the Solar System" I would place 2003EL61, with its 3D ellipsoidal shape and assumed 4h rotation period higher in the bizarreness ranking. Provided that they have not mistaken a 8h-period of a 2-spotted surface with a 4h-period. Regards.

MeteorWayne · Aug 21, 2007

That's a good choice. IMHO, though, almost every object in the Solar System seems to be unique. Are any two "objects" (snowflakes <img src="/images/icons/smile.gif" /> ) identical? Of course not. Each unique Gas Giant, Ice Giant, Rocky planet, Dwarf Planet, Asteroid, KBO Comet, KBO, Sedna, Oort cloud comet adds to our knowledge of one stellar environment. OK, it's ours, and we get to examine it close up. That's a good foundation for understanding new discoveries. Every new planet discovered around another star adds to our understanding of how things really work. This is a great time to be alive <img src="/images/icons/smile.gif" /> <div class="Discussion_UserSignature"> But the Krell forgot one thing John. Monsters. Monsters from the Id. I really, really, really, really miss the "first unread post" function </div>

vogon13 · Aug 21, 2007

I've also been contemplating the final few orbits of (hypothetical) ring material about Iapetus prior to it's emplacemnt onto the ridge system. As mentioned earlier, the final orbits time out at just under 3 hours, and the speed is ~1550 km/ hr. In 3 hours, what changes in the vicinity of Iapetus ?? As it turns out, not much. Iapetus takes nearly 80 days to orbit Saturn, Titan takes ~16 days. Jupiter passes sunward at intervals over 30 years. So tidal variation interactions, over 3 hours, amount to not very much at all. The gist of this is, if a given ring particle passed over a particular high spot on the Iapetan surface at an altitude of precisely 1 meter, 3 hours later, it is going to pass over that spot again at very nearly that precise altitude again, barring dissipation (or more correctly, redistribution) in the ring itself of orbital energy. Depending on the relative intensity of the 'bump process' (described earlier in this thread, and in greater clarity in the excellent The New Solar System book chapter on planetary rings) the given decay of the specific particle's altitude might be miniscule, from one orbit to the next. Where it really gets interesting is in that final orbit. A given particle can clear a pinnacle on the Iapetan surface by any tiny increment you care to imagine, even microns. But if the particle contacts that point, we are instantly in a new regime. Bumping an adjacent particle in the ring can only transfer tiny amounts of energy between the particles due to their almost identical speed. Contacting the surface, where the full speed differential of ~1550 km/hr is apparent, even in a glancing fashion, will sap significant energy from the orbiting ring particle. In a glancing contact, the ring particle will potentially be set to rotating, possibly causing it to disrupt should it's mechanical strength be low. The particle might shatter from the contact too, if the contact is anythi <div class="Discussion_UserSignature"> TPTB went to Dallas and all I got was Plucked !!So many people, so few recipes !!Let's clean up this stinkhole !! </div>

Smersh · Aug 22, 2007

Am I right in that I had the dubious honour of being sandwiched between your 16,383rd and 16,384th posts here? <div class="Discussion_UserSignature"> <h1 style="margin:0pt;font-size:12px">----------------------------------------------------- </h1>Lady Nancy Astor: "Winston, if you were my husband, I'd poison your tea." Churchill: "Nancy, if you were my wife, I'd drink it."Website / forums </div>

vogon13 · Aug 22, 2007

16,383 was made in Free Space. So you were not the filling in a vogon sandwich. <img src="/images/icons/tongue.gif" /> <div class="Discussion_UserSignature"> TPTB went to Dallas and all I got was Plucked !!So many people, so few recipes !!Let's clean up this stinkhole !! </div>

3488 · Aug 22, 2007

Hi vogon13. Yes will be true if the mountain ridge indeed id a collapsed ring. If so, than it will look very smooth at high resolution, unless pitted by tiny impact craters. If it is, they will be deep, a bit like some of the craters on hyperion, only very much smaller. If there are cryovolcanic flows & the ridge is of internal origin, than this encounter will definately answer that question. I agree with you though & I expect the ridge to look fairly featureless. Do you think it will show banding or be completely featureless?? I think that Smaersh will be extremely disappointed to learn that he is not the filling in a Vogon sandwich!!!! <img src="/images/icons/laugh.gif" /> Andrew Brown. <div class="Discussion_UserSignature"> "I suddenly noticed an anomaly to the left of Io, just off the rim of that world. It was extremely large with respect to the overall size of Io and crescent shaped. It seemed unbelievable that something that big had not been visible before". Linda Morabito on discovering that the Jupiter moon Io was volcanically active. Friday 9th March 1979.http://www.launchphotography.com/ http://anthmartian.googlepages.com/thisislandearthhttp://web.me.com/meridianijournal </div>

jaxtraw · Aug 22, 2007

Probably pointlessly irrelevant here, but I just worked out on the back of a handy *** packet that the kinetic energy of ring particles impacting (based on vogon13's statement of their velocity) would be around 92kj/kg. Or 92 Jg-1, whatever. So whether they'd melt on impact or not would be dependent on what the ring was made out of, and what temperature it was at. For instance a water ice particle at say -200C wouldn't melt entirely on impact since water ice would require 4.3J/g/degree K. Not sure whether it's relevant or not. I'm just thinking about whether there'd be some structure left or not, kind of thing. Feel free to ridicule my feeble attempts at physics here <img src="/images/icons/smile.gif" />

vogon13 · Aug 22, 2007

I have observed high speed photography of (apparently 0F) ice cubes contacting a surface at various angles at ~500 km/hr. Instantaneous pulverization occurs, and amazingly to me (at least) the contact surface did not apear 'wetted'. Appreciate someone doing some math around here. The precise velocity of the ring particles at contact is 1547 km/hr, and there is a small decrease in speed with altitude. Additionally, a rotating Iapetus will affect the touch down speed somewhat. In today's era, the speed of the Iapetan surface (with respect to the fixed stars) is <5 km/hr. For a ring system emplaced 3.7 billion years ago, if Iapetus had not yet achieved tide lock with Saturn, that number is larger. Perhaps significantly larger. While not specifically address in the New Solar System planetary ring chapter, I gather the ring is 'required' to form in a prograde orbit, regardless of the original configuration of the nascent ring materials, so all these velocities subtract from the 1550 number. <div class="Discussion_UserSignature"> TPTB went to Dallas and all I got was Plucked !!So many people, so few recipes !!Let's clean up this stinkhole !! </div>

jaxtraw · Aug 23, 2007

Well, I just realised I forgot the latent heat of fusion (bit rusty, heh). 92kj/kg doesn't even come close, so water ice may smash when it hits the "heap" but it won't melt. So we ought to see a pile of powdered ice <img src="/images/icons/laugh.gif" />

3488 · Aug 23, 2007

I suspect that is what Cassini will reveal on: Monday 10th September 2007. Cannot wait. Andrew Brown. <div class="Discussion_UserSignature"> "I suddenly noticed an anomaly to the left of Io, just off the rim of that world. It was extremely large with respect to the overall size of Io and crescent shaped. It seemed unbelievable that something that big had not been visible before". Linda Morabito on discovering that the Jupiter moon Io was volcanically active. Friday 9th March 1979.http://www.launchphotography.com/ http://anthmartian.googlepages.com/thisislandearthhttp://web.me.com/meridianijournal </div>

vogon13 · Aug 27, 2007

I note that the 8/18/2007 edition of Science News has our little Iapetus as the cover article! Article goes over what we know to date and sets the stage for the upcoming 9/9/2007 encounter. I note they reiterated the Matson, Castillo-Rogez concept. The difficulties with applying their idea to Iapetus remains an internal process to Iapetus being 'aware' of the precise location of the equator and it's 'ability' (sorry to anthropomorphize so much) to generate precisely (less subsequent cratering damage) identical diverging subsidiary ridges north and south of the main equatorial structure, and have all three ridge structures delineate exact great circle paths about Iapetus. <div class="Discussion_UserSignature"> TPTB went to Dallas and all I got was Plucked !!So many people, so few recipes !!Let's clean up this stinkhole !! </div>

vogon13 · Aug 27, 2007

Science News also mentions Ip's article in Geophysical Research Letters (2006) {I am assuming Ip has been able to revise and extend his ideas since then.} Notably, his thought that the ring would 'precipitate' 360 degrees about the equator. I recall having a similar idea early on, and it just isn't feasible to have that scenario generate anything like the ridge we see. The 'ah-ha' moment for me was to imagine thousands of ATSP satellites in orbit about our moon, and 'watching' (minds eye) them all decay their orbits. Where do they preferentially strike the surface ?? THE HIGH SPOTS !!!! And then we just contemplate what happens when the entire ring system encounters a fixed obstruction on the equator. Plinko !!, you get a ridge stretching away from the contact spot, decreasing in height as you go down range. The 'angle of repose' of the materials emplaced (just thought of this) will also 'relax' as you go down range due to the 'splat effect' at the contact point having more time to work on the (horizontal) debris plume as it hurtles downrange, and it spreads slightly north/south as you go. The angle of repose of the sides of the ridge (both north and south slopes) changes smoothly (steadily decreasing) from the high end to low, and is exactly symmetrical on the north and south surfaces I am not qualified as a mathematician to judge the resulting sloping ridge with smoothly varying side surface slopes as a 'horizontal Gaussian splat', but that is just what it is. Inclined elements of the ring system (or conversely, a slight deflection of the Iapetan rotation axis during emplacement) will generate precisely symmetrical, diverging 'sub ridges' (the notorious off ramps) that also follow great circle paths about Iapetus. And this is exactly what we see. Sweet. <div class="Discussion_UserSignature"> TPTB went to Dallas and all I got was Plucked !!So many people, so few recipes !!Let's clean up this stinkhole !! </div>

3488 · Aug 27, 2007

Thanks vogon13. Please keep us updated. I will ask the moderators if this can be made a stickie. Cassini is doing well & all looks good for the encounter on the 10th September. We WILL have much to talk about then. I think the collapsed ring theory IS the correct one. Cheers vogon13. Andrew Brown. <div class="Discussion_UserSignature"> "I suddenly noticed an anomaly to the left of Io, just off the rim of that world. It was extremely large with respect to the overall size of Io and crescent shaped. It seemed unbelievable that something that big had not been visible before". Linda Morabito on discovering that the Jupiter moon Io was volcanically active. Friday 9th March 1979.http://www.launchphotography.com/ http://anthmartian.googlepages.com/thisislandearthhttp://web.me.com/meridianijournal </div>

brellis · Aug 27, 2007

with this ring, I thee ... may I have the ring please? woops <img src="/images/icons/laugh.gif" /> <div class="Discussion_UserSignature"> I'm a recovering optimist - things could be better. </div>

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