Approaching Iapetus - what makes it two-faced?

vogon13 · Sep 19, 2007

The best 'scratches' (IMO) are south of 'Landslide Crater' (Joan) seen in the first flyby. Possibility exists they are the result of crustal inflation on the flight path of the 'Joan' impactor. I am not sure the other chasms we are seeing are similarly engendered. <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 · Sep 19, 2007

WOW, that mosaic is just incredible. I have dowloaded & saved it. Antmartian, rlb2, swampcat & FranOntanaya now yourself, you members IMO produce better images than NASA / JPL themselves sometimes. The standard of images being posted (or linked to) on these threads is incredibly high. Very professional. For what is worth, heres a NASA / JPL image of Iapetus obtained on Friday 11th November 2005 showing the whole of Joan. Enlargement of Joan. My crappy attempt. <img src="/images/icons/rolleyes.gif" /> Hi Vogon, also do you think that some of the compressional features to the east of Joan are due to crustal compression from the impact? Another thing, is there any evidence of antipodal hills where the shock waves converged directly opposite Joan, like the 'Weird Terrain' on Mercury, directly opposite the Caloris Basin? Jupiter's Callisto lacks this, as there may be a deep underground liquid brine layer, that dampened out the shockwaves before they could converge opposite Valhalla. I need to really study the Iapetus imagery, to see if this has happened. It could reveal much about the interior. The 'smoother' terrain of the central portion of Joan, I think is a palimpsest (there are many of these on Jupiter's Ganymede & Callisto). Cannot say that I have noticed any on Rhea (maybe have not looked hard enough). <img src="/images/icons/tongue.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>

h2ouniverse · Sep 19, 2007

I've uploaded spin0's link: the kind of picture that is a reason for life in itself... (more briefly: wow) Thank you spin0 If Iapetus has cooled down very quickly, without full differentiation, the concentration of ammonia in the ice close to surface should be relatively high. And ammonia-rich ice breaks easily under thermoelastic stresses, with big sound waves, [a kind of glass state]. May it explain the scratches? Other explanation (as Vogon suggests), not incompatible given this glass-like behavior: the impact. There are similar lines, although less deep, on Callisto (concentric lines as waves around an impact crater). It would be interesting to see whether the scratches can be assimilated to arcs of concentric circles... Regards.

3488 · Sep 19, 2007

Hi Joel, Could well be IMO. I would think that it would be possible to map the Tiger Scratches, to see how they relate to known impact features, such as Joan. I am very familiar with the Galilean Moons of Jupiter as I have researched them thoroughly. I am not so familiar with Saturn's brood as yet, but this thread, along with the Enceladus & various Saturn / Titan / Cassini threads have helped me enormously. SDC IS a very good place to learn new things. BTW with Callisto, the inner 14 rings of Valhalla are overlapping, wide 'steps', where as the 11 on the outside are graben (sunken valleys) instead. This was not noticeable until the Galileo close encounters (although Voyager 1 did image them but not at sufficient resolution). If possible to map Iapetus's 'Tiger Scratches', it will be interesting to compare. BTW APOD for Wednesday 19th September 2007, of the Voyager Mountains. 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>

h2ouniverse · Sep 19, 2007

Hi Andrew, Thank you for the detailed explanation for Callisto. Do you have a sketch of the cross-section of the Valhalla rings? Regards

brellis · Sep 19, 2007

Great mosaic spin0 <img src="/images/icons/cool.gif" /> Fascinating discussion you's are having about what makes Iapetus tick. I'm enjoying every moment of it! <div class="Discussion_UserSignature"> I'm a recovering optimist - things could be better. </div>

h2ouniverse · Sep 19, 2007

Andrew, I just realized you had a lready a post about Callisto at 5:17. Actually you posted at 5:17 as I was preparing a post linked to Vogon's post (finally sent at 5:35). A coincidence that we both thought to Callisto at the same moment!!

3488 · Sep 19, 2007

Hi Joel, I have PM'd you with a whole load of Valhalla Callisto stuff. It is just that I can see certain parallels between Iapetus & Callisto. Hi brellis, I am enjoying this very much too & hope that other members of SDC feel that my input is worthwhile. 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>

3488 · Sep 20, 2007

Iapetus from 1,664,006 kilometers. Iapetus here looks like a one eyed Cyclops with an ear!!!!! Anyway, Iapetus is now looking a bit small to Cassini. Just waiting for the SAR imagery & other stuff to be released. 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>

h2ouniverse · Sep 26, 2007

Hi Andrew, I saw your Valhalla images. Thanks. Well, it's true that there are steps on Callisto that do not look like the cracks on Iapetus. But there are also "cracks" more Iapetus-like, at least viewed from far... Regards.

CalliArcale · Oct 1, 2007

Since the flyby is over and there hasn't been any recent activity on this thread, I'm going to unpin it now. <div class="Discussion_UserSignature"> "People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff." -- The Tenth Doctor, "Blink" </div>

3488 · Oct 8, 2007

New Iapetus stuff. NASA / JPL Planetary Photojournal. Highest resolution mosaic. Heavily cratered Voyager Mountains. Voyager Mountains. Ultraviolet Iapetus. Water ice & CO2 ice on Iapetus. Water ice & CO2 ice properties on Iapetus. High resolution temperature strip on Iapetus. Complex Transition on Iapetus. Trailing Hemisphere of Iapetus. A complex surface on Iapetus. Transition Zone. 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>

anthmartian · Oct 8, 2007

Thanks loads for that. <img src="/images/icons/smile.gif" /> *is busy downloading* <div class="Discussion_UserSignature"> "Traveling through hyperspace ain't like dusting crops, boy! Without precise calculations we could fly right through a star, or bounce too close to a supernova and that'd end your trip real quick, wouldn't it?"Han Solo - 1977 - A long time ago in a galaxy far far away.... Click Here And jump over to my site. </div>

3488 · Oct 8, 2007

You are very welcome. <img src="/images/icons/laugh.gif" /> It is great to see the results from the encounter now becoming official, although here on SDC, we have already produced a fair few ourselves. <img src="/images/icons/laugh.gif" /> The warmest region on the Cassini Regio @ the equator / tropics is really 'warm', - 145 Celsius / 128 Kelvin. That is comparable to the average of the Galilean moons of Jupiter. The reason being that Iapetus is a slow spinner (approx 80 days) & a dark surface, absorbs what little solar energy there is. 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>

franontanaya · Oct 8, 2007

Very interesting. According to the spectrometer data, the ice in the V shaped area, slightly left of center on PIA08381, seems to have particularly less Rayleigh scattering (dirtier?) than everywhere else. <div class="Discussion_UserSignature"> </div>

brellis · Oct 9, 2007

NASA Article NASA scientists are on the trail of Iapetus' mysterious dark side, which seems to be home to a bizarre "runaway" process that is transporting vaporized water ice from the dark areas to the white areas of the Saturnian moon. This "thermal segregation" model may explain many details of the moon's strange and dramatically two-toned appearance, which have been revealed exquisitely in images collected during a recent close flyby of Iapetus by NASA's Cassini spacecraft. ... Using multiple instruments on Cassini, scientists are piecing together a complex story to explain the bright and dark faces of Iapetus. But yet to be fully understood is where the dark material is coming from. Is it native or from outside the moon? It has long been hypothesized that this material did not originate from within Iapetus, but instead was derived from other moons orbiting at a much greater distance from Saturn in a direction opposite to Iapetus. Scientists are now converging on the notion that the darkening process in fact began in this manner, and that thermal effects subsequently enhanced the contrast to what we see today. hmm. I think a piece is still missing from the puzzle. <div class="Discussion_UserSignature"> I'm a recovering optimist - things could be better. </div>

3488 · Oct 9, 2007

Hi FranOntanaya, I suspect that is what it is. If the ice is dirtier, there will be less Rayleigh scattering, as the particle size of the contaminents, will be too large, to allow for said Rayleigh scattering. Hi brellis, Which part of the puzzle is missing IYO? The distribution of the CO2 ice is interesting as it appears to be mostly on Cassini Regio. The general idea is that the contaminents are from Phoebe, but also suggested earlier by Vogon13, that some of it at least is from Titan's atmosphere (some caught by Hyperion too). I suspect both reasons apply here. 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>

tdamskov · Oct 9, 2007

This "thermal segregation" model may explain many details of the moon's strange and dramatically two-toned appearance, which have been revealed exquisitely in images collected during a recent close flyby of Iapetus by NASA's Cassini spacecraft. <blockquote>In reply to:<hr />hmm. I think a piece is still missing from the puzzle.<hr /></blockquote> I think you're right. The article presents the case as if it's basically solved and closed. Perhaps this is simply due to the way it's presented in the media, I can't quite tell. Personally I like this theory - on a general basis it fits neatly. The article basically claims that all the dark/light material is recent and covers the primeval mixed dirt/ice surface below. The mechanism that keeps the surface covered must be very busy at work since we see so little evidence of recent cratering. I would love to see something similar to the Deep Impact mission on Iapetus <img src="/images/icons/smile.gif" />

3488 · Oct 9, 2007

Hi tdamskov, Vogon13 & myself are going to try to convince NASA /JPL to get the Cassini Orbiter to impact Iapetus, at the end of the mission, into Cassini Regio. I will suggest that the Cassini spacecraft, transmit monochrome images, using the narrow angle camera, during said approach & transmit them in real time (bypassing the usual rigmarol of storing images onboard & transmitting them later). This will enable not only further science in the dying moments of the mission, but also to pinpoint the impact site precisely, so a future Saturn system / Titan craft, during approach can examine the area, using remote sensing, to see if the darkening is still happening & if so, at what rate. A Deep Impact type mission would work in theory, main problem though, is that Iapetus has a 2% surface gravity, where as Comet Tempel 1's surface gravity is what 1 in 250,000, or less, much easier to generate a large plume. IMO, in the case of Iapetus, the impactor would have to be very large, heavy & very fast to generate a meaningful plume, for the mother ship to examine. 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>

tdamskov · Oct 9, 2007

<blockquote>In reply to:<hr />Vogon13 & myself are going to try to convince NASA /JPL to get the Cassini Orbiter to impact Iapetus, at the end of the mission, into Cassini Regio. <hr /></blockquote> That sounds like an excellent idea. Compared to the Deep Impact mission, do you have an idea of the possible energy release by an impact of Cassini on Iapetus?

3488 · Oct 9, 2007

To be honest, I do not know. IMO it will be several times that of Deep Impact, Cassini is much more massive, but may not be travelling very fast however, as Cassini, is likely to be at Apokrone (furthest point in an orbit around Saturn). Having said that though, the gravity of Iapetus, may be enough for some acceleration prior to impact. What we are looking for is to create an impact crater, in a location & @ a time of our choosing. There are bound to be follow up missions to the Saturn system, most likely a dedicated Titan orbiter, which prior to arrival at Titan, could pass close to Iapetus & image the impact location, to see, if the fresh impact crater, has become darker, etc. I do not know if a Cassini spacecraft impact on Iapetus, would be visible to Hubble & / or Spitzer. I doubt it very much, but who knows. 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 · Oct 9, 2007

BBC Article New data from the Cassini spacecraft seems to confirm Iapetus is picking up dusty material on its bow front. But, say the mission's scientists, this material is then being warmed by the Sun's rays, making it go even darker as it loses water vapour. With this vapour then depositing itself as ice on whiter, colder areas of the satellite, there is a process in play on Iapetus which turns up the contrast - the dark, dirty regions get even darker; and the light, icy regions get lighter. Researchers say they still have some way to go to fully understand what is happening at this remarkable moon. In this article, it's not presented as "problem solved" - that was my concern about the previous article. <div class="Discussion_UserSignature"> I'm a recovering optimist - things could be better. </div>

vogon13 · Oct 10, 2007

More on impacting Iapetus: This Cassini crater is going to be around for a while, it might as well be located in a spot where we might like to put a rover mission after the next flyby/orbiter. I'm thinking not too far from the wedge ramp, and maybe near a black'white boundary, but not so close as to risk the impact in a white region. Additionally, some of the craters and their surroundings have a differing degree of saturation or tone in the black coloration, we might want to examine why there is a difference, and which we want to encrater. <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 · Oct 10, 2007

Additionally: it is looking more and more likely an inclined 'brim' on the outer edge of the Iapetan ring system was responsible for the symmetrical diverging attendent ridges. Many ideas have been explored (here and elsewhere) to explain the 'off ramps' and inclined elements in the ring seem likely to have formed (combination of Saturn proximity and the inclined Iapetan orbit) 'automatically' during the collapse to the Laplacian plane of the original impact lofted debris. 'Occam's Razor' gives this idea the nod as it is by far the simplest. {My very first post here on Iapetus, that I had snarkily suggested would be acclaimed as 'prescient', is actually somewhat beyond 'prescient' now, and is approaching eerily spooky.} <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>

paulscottanderson · Oct 10, 2007

According to the original Cassini press release, the collapsed ring theory is considered less likely now to explain the ridge: http://saturn.jpl.nasa.gov/news/press-release-details.cfm?newsID=779 "Some other mysteries are coming together. There are more data on the signature mountain ridge that gives Iapetus its "walnut" appearance. In some places it appears subdued. One big question that remains is why it does not go all the way around. Was it partially destroyed after it formed, or did it never extend all the way around the moon? Scientists have ruled out that it is a youthful feature because it is pitted with craters, indicating it is old. And the ridge looks too solid and competent to be the result of an equatorial ring around the moon collapsing onto its surface. The ring theory cannot explain features that look like tectonic structures in the new high resolution images." <div class="Discussion_UserSignature"> -----------------The Meridiani Journal a chronicle of planetary exploration web.me.com/meridianijournal </div>

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