Hi,
CASSINI has transmitted 184 pics (!) over the last days.
Here five takeouts, 3-4x enlargement:
They certainly took enough images this time around. There must be at least a hundred new ones.
[Edit: oops, 184; didn't read the above post carefully the first time.]
At the end of November, Cassini will be a bit over two million kilometres from Iapetus. That hardly even qualifies as a "distant encounter" -- it's really just plain "distant".
Nonetheless, looking at the Solar System Simulator for dates around November 25th, any images taken around this time will probably be nice to look at, because they should show a bit more of the trailing, light-coloured part of the Saturn-facing hemisphere, Roncevaux Terra, than we have seen before. (Of course, we've seen some of it relatively close-up in Saturnshine during the New Year's 2005 distant flyby.) Cassini will be near apastron then, so there should be a bit of free time for taking pictures of Iapetus.
We haven't seen much of this part of Iapetus in previous Cassini images. My impression (correct me if I'm wrong) is that this is due to the geometry of Cassini's orbit around Saturn, up to the present time. Whenever Cassini is well placed to photograph the trailing side of Iapetus, it will normally also be very close to Saturn, which means that other things would naturally take priority over getting fuzzy pictures of a moon three million kilometres away.
I just used the Solay System simulator and I have the following:
Date: November 27, 2006
Time: 00 hours (UT)
Distance: 2.008 million km
A full disk view of the Saturn facing hemisphere of Iapetus at 12km/pxl
I'm sure with multiple images and super ehancement, we can fill in a imaging gap of Iapetus
in the high northern latitudes at better than the 9km/pxl that Voyager 2 achived in 1981.
Hi,
here what you're talking about:
I can't wait to see that!
[something went wrong here]
I created the same image with Xplanet and Steve Albers' map:
I think that super-resolution processing may be needed to pull any nice looking images out of this. But that would have to wait for the PDS release (Stacking the "raw" jpegs will help compensate for compression artifacts, but does litttle else to improve resolution.
Hi again,
new release in the NASA/JPL image gallery - 'Duotone Moon':
Date: 2006-09-06
Distance: ~2.2 mio km
Resolution: 13 km/pxl
Bye.
I used NASA's space simulator a lot in the past, but I think their maps aren't quite as good as Steve Albers' maps.
As TritonAntares said, the key is that the illumination conditions will be different. This "flyby" may be useful for albedo mapping.
Hi!
The lower left image is the same as the one I made a while ago, using stretched color, but toned down to better match the approximate true color. The contrast is stronger in my composite so darker details aren't very visible, though: http://static.flickr.com/105/281244148_a2b17953f1_o.png.
There's also the http://ciclops.org/view.php?id=624 showing the same image sequence in stretched color.
Hi!
CASSINI took another few Iapetus images about 10 days ago,
here 3 of them:
That recent small sequence is really striking to me; Iapetus looks a lot like a CD or DVD!
In fact...is this significant or coincidental? It looks like the dark area subtends a suspiciously well-defined angular area in this view (90 deg of the total spherical area of Iapetus?), which in turn would seem to argue for external deposition from some source. In any case, the geometry of the dark area is remarkable.
I suspect a thermo-reactive gas is introduced into the Iapetan environment at a fixed point in its' orbit about Saturn. Most likely when Iapetus traverses the Saturnian magnetotail.
The gas persists in the vicinity of Iapetus, and in equatorial to the midlatitudes the Iapetan surface temperatures are sufficient for the gas to 'tholinize' and coat the surface. The gas is used up (or dissipates into the void) in less than the ~80 days it takes for Iapetus to return to the place in it's orbit where the gas is replenished, thus, we do not see the darkening extending further around in longitude than we do.
That there is some 'ponding' of the gas in low areas seems apparent, there is some darkening outside of the main areal extent of Cassini Regio in the lower latitudes.
Additionally, the more directly perpendicularly sunward facing segments of crater bowls north and south of Cassini Regio also show the darkening, as expected, the local heating conditions being sufficient for the chemical staining reaction to occur.
The gas also appears to interact with Hyperion. Quantities of it appear to pond in the craters, and when the chaotic rotation of Hyperion causes the sun to shine perpendicularly into a given crater, the crater bowl reflects enough solar radiation onto the crater floor to make a local warm spot. The gas reacts, and we get dark crater bottoms all over Hyperion.
The same basic mechanism, a thermo-reactive gas being introduce into the Hyperionian and Iapetan environments, explains the dark areas of each moon.
That is both an interesting and highly creative hypothesis, Tasp. Skeptical questions must follow, though:
1. What is the nature of this thermoreactive gas? I presume that it is being scattered off of Saturn's upper atmosphere somehow.
2. Why do no other moons but Iapetus & Hyperion exhibit any apparent effects from this environmental condition? Probable minor compositional differences do not seem adequate. Additionally, this thermoreactive agent would presumably have a relatively high molecular weight, and therefore its transport throughout the region would not necessarily be confined to the outer limits of Saturn's magnetosphere in accordance with magnetic current flow patterns.
Sorry; I am not trying to put you on the spot at all...just trying to flesh out this most interesting thought of yours, which would have never occurred to me!
The gas comes from Titan's atmosphere. This implies only objects exterior to Titan's orbit will experience the darkening as there is no transport mechanism running from Titan inward.
The atmospheric gases of Titan contain carban and nitrogen and hydrogen. The thermosensitive chemical reaction (way out of my schooling here) might be a polymerization of those Titanian gases. I suspect the orange color of Titan and the rich brown of Iapetus are derived from similar compounds and elements.
I don't know if slow steady leakage of atmospheric gases from Titan is what is happening, or if big impact events on Titan liberate gases sporadically.
Maybe both processes have occured over the history of the solar system.
Hi!
CASSINI took another few Iapetus far distance images 3 days ago,
here a takeout:
Here's the http://space.jpl.nasa.gov/cgi-bin/wspace?tbody=608&vbody=-82&month=11&day=27&year=2006&hour=10&minute=00&fovmul=1&rfov=0.273&bfov=30&porbs=1&showsc=1 pixel size Iapetus will appear on Nov 27. Obviously not that useful except for low phase observations.
Hi once again,
CASSINI took another four Iapetus far distance images,
here a takeout:
Date: 2006-11-16
Distance: 3.128.691 km
Filters: CL1 and CL2
View with Solar System Simulator:
Hi,
CASSINI took a series of 41 Iapetean far distance pics yesterday,
here a first takeout:
Hello again,
I always wondered about the dark patches in Iapetus' bright region Roncevaux Terra as seen on this map:
I would not know either. But we will know alot better after September 10, 2007 when Cassini will image this area with resolution as good as 200m per pixel!
Hi,
nice pic Phil - I didn't notice the 2 originals on the JPL/NASA page at all.
It'll may help to measure the depth of Snowman A and the hight of its central peak...
Have you tried to combine some of the Nov.27th images, probably getting some colored ones?
Bye.
Hallo,
one probably better resolved and enlarged pic of the last far-encounter http://saturn.jpl.nasa.gov/multimedia/images/image-details.cfm?imageID=2435.
Date: 2006-11-27
Distance: ~2 mio km
Resolution: 12 km/pixel
Sadly no color composite...
Bye.
Colour composite with Lightness channel consisting of 10 stacked images:
Is Roland the prominent crater at the 11 o'clock position?
My version made from one RVB picture (saturation at 200%) and 10 b&w stacked and added pictures. 200% approx. size.
Pink Iapetus, now that's something you don't see every day!
ugordan: "Pink Iapetus, now that's something you don't see every day!"
It's a Valentine!
Phil
Huh...that "yin-yang" aspect makes Iapetus look like one of the hemispherical views of Fritz Leiber's The Wanderer...art imitating life in yet another subtle way, albeit decades in advance.
Just struck me also how deep & pronounced all these craters are in comparison to those on the inner large icy moons. Is this difference perhaps due to fallout from Enceladus on the latter, as discussed on another thread, or are we seeing evidence of a thicker crust on Iapetus?
Hi,
I've just checked the JPL raw images page for new iapetean pics - and was successful:
189 new images between Feb.12th and 16th (!)
Looks like there has been a shadow casting show by saturn during this time on Iapetus...
Here some takeouts:
Confirmed
http://space.jpl.nasa.gov/cgi-bin/wspace?tbody=10&vbody=608&month=2&day=14&year=2007&hour=02&minute=00&fovmul=1&rfov=10&bfov=30&porbs=1&showsc=1
No way! Mega cool!
Stretched color snapshots at the start and near maximum eclipse:
Way nifty. Here's an animation of the February 14 set, magnified 2x. Note that since this is during an eclipse, the ones that aren't in eclipse are necessarily pretty much zero phase.
Actually, not necessarily zero phase. Remember this isn't the case where the observer is located on the body that's casting the shadow. I get a 14.5 degree phase from Cassini's vantage point at Feb 14, 02:00 UTC
Oops! Thanks for the correction. Glad I got it here before I posted the wrong thing in the blog
--Emily
I noticed the "darkened" images of Iapetus and wondered what had caused that -- it never even occurred to me that it might be Saturn's shadow. Neat.
Btw, I once (2006-03-14) posted this:
Interesting . . .
Iapetus traversing the Saturnian shadow and the Saturnian magnetotail. Effluvia wafted from the Titanian atmosphere possibly lofting into Iapetus' space . . . .
This is probably an FAQ for the unhip (and please feel free to slap me if needed!), but will Cassini get any really good views of the dark/light border areas this September? Seems as if that's key for determining the origin of the Great Dark Splat...
Thanks, TA & Rob.
Main thing is that we need to examine the border region with as much high-res as possible. The outer edges of the deposit should provide some clues on exactly how this stuff was laid down. Abrupt or very gradual borders could indicate a radiational origin as Tasp suggests, while streaky, irregular borders would suggest either an eruptive origin or infall from somewhere else.
We might note a correlation between degree of darkening, altitude, and longitude in the light/dark coverage.
Seems like a mathematical model or simulation analyzing sun exposure (insolation), local slope, altitude, longitude, and the Iapetan parameters of ~80 day long 'days' and introduction of a gaseous discoloring agent at aphelion could be made. Program needs to be recursive, the darkening modifies the local temperature and facilitates further darkening.
Interesting if someone comes up with some random topology to run through the program to see if it generates Cassini Regio like stains on the object.
Or tackling the problem the other way round, someone (more capable with math than I) confirms images of Cassini Regio darkening does correlate with altitude, local slope, longitude, and insolation . . .
Hi,
I just http://photojournal.jpl.nasa.gov/catalog/PIA08902 that the Iapetuseclipse in february was actually caused by Saturn's rings:
Cool; didn't know that either, thanks!
Hmm. Anybody know exactly how much the illumination is cut down during these events? The total solar energy @ Saturn is only about 15 W/m^2. I can't tell how much loss happened during the Iapetus eclipse, but seems as if knowing that based on Cassini's imaging capabilities might provide some interesting data on the properties of the B-ring.
There was also some pre-Cassini info on the B-ring attenuation from the occultation of 28-Sagitarii in 1989 visible from Earth. I watched this visually in my 6" telescope and could see the star fluctuate in brightness. Perhaps there are more accurate measurements that were made?
Also, I believe there were stellar occultations of the rings observed by Voyager and Cassini.
In any case it might be challenging to measure the densest portion of the rings.
A Voyager watched a stellar occultation by the entire rings with the (partly crippled) Photo-Polarimiter instrument. With a very high data sample rate, it got radial sampling across the rings of a few ?10's? of meters... Astonishing structural detail. Cassini uses the UV instrument for this, I think. (Voyager also got UV occulation at lower resolution)
The radio science occultation data was limited ... INITIALLY ... to the kilometers-sized beam-spot of the diffraction pattern of the radio beam on the rings. .. That was until they processed the data with time/frequencey analysis much like the synthetic aperture radar processing and got nearly diffraction (and signal-to-noise) limited resolution in the rings. Note that the 2-frequency radio saw dramatic differences in ring opacity at S and X-band wavelengths.. directly due to different abundances of ring particles in the size range difference between the 2 wavelengths!
The B ring is highly opaque, and the shadow on Saturn is essentially truely black. Even multiple scattered light filtered-through the rings barely illuminates b-ring particles on the shadow side of the rings in the most opaque areas, even in long exposures
Today I was looking at a rendering I created this morning, I noticed a weird spot on Saturn:
It apears to be a shadow of Iapetus, traversing Saturn's disk!
Cool! This is no doubt on Cassini's imaging todo list.
You can see that using the Solar System Simulator too. Just enter "Iapetus seen from Saturn" for 6:50 UTC March 27th.
It looks like a near-miss in the Simulator, but that's just because it's off Saturn's centre a bit. Looks like roughly 10% of the Sun's light was blocked during this transit, at any particular spot under the penumbra.
I hate to burst everyone's bubble, but no images of that are planned. Sorry. Would have been cool though.
From the latest PDS batch, here's an approx. natural color composite of Iapetus from June 2006 and alongside it a view from November 2005 showing almost the same hemisphere, but with different illumination:
http://m1.freeshare.us/view/?130fs65107.png
Both images magnified 2x from original pixel scales.
Let me just mention the far encounter later this month -
finally a chance to see another form of shadow casting at the Snowman as Iapetus left side is now in dark...
Here's a stereo view that gives a pretty good idea of the Snowman/Moat topography.
http://mysite.verizon.net/vzepeq2k/iapetus/id3.html
Michael
No, it really is November 2005. The January 2006 encounter was more distant, in fact I've got the entire sequence assembled into an image and an animation. It can be found http://www.flickr.com/photos/ugordan/345441934/.
The distant approach images from November and January are pretty similar, but if you look closer the January images show more of the Snowman in sunlight.
That November 2005 image is interesting for another reason. Look at the 8 o'clock position on Iapetus' limb. You can see one of the large basins in profile. This one isn't normally as easy to pick out as some of the others.
It looks to me like the upcoming April 15th shots of Iapetus might have a chance of catching the big Roncevaux Terra basin in a similar profile.
Hi,
here some infos about the upcoming far-encounter:
april 15 -> 2 clear und 19 color images
april 17 -> 1 clear, 6 color and 3 WAC-images
april 18 -> 2 clear, 34 color and 2 WAC-images
april 21 -> 2 clear, 6 color and 2 WAC-images
Resolution (NAC) will be about 14 km/pxl.
Bye.
More food, Iapetus hounds:
http://saturn.jpl.nasa.gov/multimedia/images/raw/raw-images-details.cfm?feiImageID=107531
For fans of Roncevaux Terra, the first set of Iapetus images from this very distant encounter are now up.
As I'd hoped, it looks as if the big trailing-side basin can be seen in profile as a "flat spot" on the moon's limb at about the 4:00 position. There seems to be a central peak visible.
There are also a couple of dark spots visible that may not have been seen before. And (once again) we get a tantalizingly fuzzy look at the Snowman crater system.
No sign of the bellyband on the moon's limb -- but 2.2 million kilometres is very long-range -- it may just not be that high at that particular point. We'll find out in a few months.
Ahh,
there they are...
Here two takeouts, ~3x enlarged:
This is a composite of four of the new images. I recall that stereo viewing of Voyager images of this northern bright area revealed apparently tectonic lineaments in this area - probably one of the old NASA TM reports on the geology and geophysics program.
Phil
If I'm not mistaken all these features show up very well on the Iapetus mosaic map on CiCLOPS. The big basin complex lower centre at about longitude 320 and the ones up north at about longitude 0. If I'm totally wrong please tell me gently.
Iapetus is a relatively small part of the image thus the image is more likey to get overstretched by the algorithm they are using. Thats what appears to have happened to the bright patches which are located in the area which is receiving the maximum sunlight.
Thanks for the composite, Phil.
In addition to the poorly known parts of Iapetus that are near its limb on this sequence of photos, we're also getting a much better look at some topography on the terminator. There are a couple of big craters on the northern terminator that have been hinted at in previous images but for one reason or another just haven't been very visible before now.
Over the course of the next few days these craters will become more visible. Cassini seems to be "chasing" Iapetus for the time being -- it will maintain about this distance for the next week or so. Perfect time for shooting stereo pairs!
Info on upcoming Iapetus imaging on Rev 43 'looking ahead' on Ciclops now.
More images appearing now.
So,
next series arrived...
Here two further takeouts, ~4x enlarged:
Iapetus, the http://en.wikipedia.org/wiki/Yin_and_yang moon
I'd rather say 'tennis ball moon'- more three dimensional and less philosophical baggage.
TritonAntares I've just created a cross-eye stereo pair from two of your recent images by photocopying them at 50 and 42 percent to match the sizes. It took only a minute to do and works a treat.
Hi,
next pics are online...
A takeout, ~4x enlarged:
My version of that latest set, 4 images merged, showing the giant basin on the terminator.
Phil
Wow - those two make a beautiful stereo pair (but you have to place them diagonally).
It looks like the big landslide basin has a subdued inner ring, or am I imagining things?
Hi again,
let me mention tomorrows far encounter of Iapetus:
And I can tell you the images of Iapetus taken on July 3 are in and ready for use.
Yep, the big basin is nicely visible -- and what's more, it's noticeably lighter in colour than the surrounding area.
That's got to have ramifications for some of the origin theories of Cassini Regio.
So, could ejecta from the big southern basin have covered up a pre-existing dark equatorial band that originally bisected Roncevaux Terra? (Theory number 7,234.)
Michael
Here's a composite of four frames, enlarged and contrast-adjusted.
Hi once again,
additional 12 pics will be transmitted on July 8th showing regions a little bit more eastern under a slightly lower resolution.
This basin really appears strange - bright and without contrast. Even its central peak is not visible.
Looks like one of those depressions of a golf ball...
I never expected it looking like this!
Bye.
This is a weird one.
The lack of bright craters in Cassini Regio indicates that the darkening process there is recent, or perhaps even ongoing.
However, the images of the RT basin from October 2004 clearly show that it is surrounded by other, smaller craters. So it must be pretty ancient (as its size would imply). It's hard to imagine how a recent darkening process could spare this basin, but affect other areas at the same latitude.
A couple of possible explanations pop up:
(1) The darkening process in Cassini Regio is different from the one in Roncevaux Terra, at least in most places. If I'm not mistaken, this has been suggested by the Cassini team.
(2) The composition of Iapetus varies with depth, with deeper material being less susceptible to darkening, and the Roncevaux Terra basin is the only one that is deep enough for this effect to be visible.
(3) Far less likely: There has been a recent impact near the middle of the Roncevaux Terra basin that has resurfaced it out to the rim with brighter material. (I don't believe this for a minute, but it's technically possible.)
Iapetus continues to confound attempts to explain it. At least September 10th is coming up. We'll just have to pray that nothing bad happens to Cassini in the next two months.
The images of Iapetus from July 8 are now in and ready to view.
Here's my version, consisting of 12 stacked images, plus a simple histogram stretch:
Hello again,
a question to be answered - which is the largest of the great basins, and what about their actual diameters?
Once again by the low-tech expedient of printing off, sliding around and glueing together I have a nice cross-eye stereo pair made from Ian R's composite above and Phil Stooke's one in post 106. It's not perfect but it works. The big bright crater definitely has a near rim and a far rim.
Anyone fancy doing it properly?
I think I might go out on a limb so to speak and illustrate my question. If you compare the two images I'm linking to you can see the first one is the existing map. The second is just the new image mapped onto hopefully the same projection. If this is correct (a big if), then the eastern edge of the basin in the new image corresponds to the central "peaks" in the basin on the previous map, kind of a double basin? If it really is one basin, then I'll be doing some refitting of the images (such as the Voyager image) to the map (it wouldn't be the first time). Where does Occam's razor lie here?
http://laps.noaa.gov/albers/sos/saturn/iapetus/iapetus_rgb_cyl_www_1k.tif
http://laps.noaa.gov/albers/sos/saturn/iapetus/iapetus_rgb_cyl.tif.0
I'm fairly confident there is no double rim, and the problem is in the reprojection, perhaps spread over both sides of the gap. The apparent crater on the east rim of the new basin fits nicely in a shadow space in the old image if things are shifted a bit.
Phil
I'll be interested to see whether things will shift enough to fully account for the offset I'm now seeing. Here are two more links. The first image is a new preliminary map with all the old and new images added. The second is the ISS map that I'm using for comparison. There are some differences though I've yet to see enough of an obvious difference that would fill the gap.
http://laps.noaa.gov/albers/sos/saturn/iapetus/iapetus_rgb_cyl.1-29.jpg
http://laps.noaa.gov/albers/sos/saturn/iapetus/iapetus_ssi_1k.jpg
One more reason to wait until September
Steve,
Could your problems be caused by the fact that Iapteus isn't perfectly spherical? I imagine that might cause some significant distortions in your image reprojections.
Ian.
Ian,
That is a possibility to consider. This might be kind of in mid-stream, as for some of the key images I've switched from a spherical assumption to using a triaxial ellipsoid that has been recently published. Hopefully my software is doing that with enough accuracy. However much of the projection error associated with assuming a perfect sphere ends up being in the north-south direction, at least for images with a sub-spacecraft point near the equator. Most of the offset I'm seeing with the basin is in the east-west direction.
The older image with the shadowed version of the basin (Oct 2004) was projected assuming a sphere, so I am thinking of redoing that one. This was released from CICLOPS with a grid overlay so I was assuming things were fairly accurately done. Another thing is that I see the Voyager image may also need to be switched over to a triaxial ellipsoid and that is a key connecting image. Perhaps this being a polar view will show more of a shift?
Hi,
http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS31/N00086061.jpg available now:
Date: most likely today
Distance: ?
Maybe someone can pump more information out of it ?
Bye.
Rob's image in post #125 is a good one to consider also. I redid my fit using the triaxial ellipsoid and allowing for a little scrunching just south of the bellyband on the western side. You can see my fit at this URL:
http://laps.noaa.gov/albers/sos/saturn/iapetus/ortho13_gridded.jpg
The western limb of this image is still quite a distance away from the Ronceveaux Terra basin. My new fit agrees pretty closely with the older one though I have an offset in both a few degrees to the NW of the ISS map. So every correction that can be made will help though there's still quite some ways to go before I can make the RT basin inconsistency go away. I think that my map agrees with the ISS map (post #122) reasonably well for the Snowman craters and with the gridded ISS image for the Voyager mountains. Perhaps one of them may have to move significantly to really close the basin gap. The Voyager mountain agreement is illustrated at this URL:
http://laps.noaa.gov/albers/sos/saturn/iapetus/ortho11_gridded.jpg
In the middle pair of images the lower one is the ISS fit and the upper one is my (still spherical) fit.
I just saw TA's new image so I'll think about that one as well. I see on the raw images page that there's no date or distance info so I wonder if the central longitude has shifted since the July 8 images?
Regardless, it is always best to use the triaxial ellipsoid radii than assuming a spherical body, particularly for Iapetus! However, keep in mind that the region we are looking at now has been pretty poorly mapped before and the DLR map may not be a good fit, yet. Hopefully, after September's flyby, we will have some better results on the control point network and the triaxial ellipsoid shape.
Could another component of the "basin gap" be that a broad basin rim shows up as shading on the eastern slopes of the (broad) rim in some lighting and as shading on the western slopes in opposite lighting?
http://www.phys.ncku.edu.tw/~astrolab/mirrors/apod/image/0211/mareOrientale_lunarOrbiter4_c1.jpg
With Mare Orientale on the Moon, for example, lighting from the east will show the eastern rim mainly as a shadow to the west of the highest level. Lighting from the west will show a shadow to the east of the highest level. This could amount to some 50-100 km perhaps if a basin's rims were really broad.
So,
yet http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS31/N00086061.jpg is online:
Date: most likely yesterday
Distance: ?
2x enlarged
Maybe someone can pump more information out of the original ?
Bye.
Looking through all the images of this far encounter I took notice of a dark structure at the eastern rim of the new bright basin in southern Roncevaux Terra:
Interesting to look in more detail at structures on the eastern side of the basin. Was it Ian who earlier composed the stacked image for July 8? This appears to show some of the features better than the single image I used in my test map. Would it be OK if I were to try using your stacked image instead to see if it shows things better?
The crescent image is one I've yet to use much in mapping, this might be interesting to give a try and see how it fits in.
It might be easier in some ways to wait until September to see how the basin images fit, yet I'll indulge a bit more in my wild speculation about the potential basin gap that I see. Following up on my mention of the crater Hamon, I will check again how it fits between the Voyager image and the July 8 views. Then using the Voyager image to fit features to the Oct 2004 imagery for the Voyager mountains and environs I think one can come up with a reasonable solution for the location of the basin (or dare I suggest basins ).
Going one tentative step further, my experimental map I think had the location of the rim feature T/A is circling to coincide with the apparent "central peaks" in the Oct 2004 imagery...
Steve, you're more than welcome to use the stacked image!
Thanks much Ian. Hopefully I'll have some time to try it during this week - given my day job and such.
Regarding the thin crescent image (and hidden answers) T/A showed from post #134, it seems to actually show a hint of a second rim in the interior of the basin, judging by the indentation in the terminator. This inner rim might not be concentric with the outer one. There is also less of a suggestion of central peaks compared with the adjacent wider crescent image to its left. This all makes me wonder further how the thin crescent image would show up if projected onto the map and if it would help in clarifying my hypothesis - in this context meaning two overlapping basins or at least an extra ring on the eastern side.
These two view of Iapetus was made from 13 and 15 pictures by stacking and quadrupling resolution with giotto 2 software.
In the phto of 18. April 2007 there seems to be a bright feature at the southwestern terminator, maybe a central peak?
I think it can be seen in the photo of 08. July 2007, too.
Harkeppler
...
Difficult to say which one exactly Hamon is, I believe this dark structure:
Nice illustration T/A. In some ways this looks possible, yet I'm thinking Hamon is the rightmost red circle you have marked in the July 8 image. Note the cross shaped pattern of craters of which I think Hamon is on the western wing.
The feature circled in green on the July 8 image may not be visible on the map you're showing, however I think I can see it in the original Voyager image.
Greetings,
I'm in the midst of reviving my mapping efforts with the thin crescent image from Oct 2004 (post #134 lower right). My initial assessment is that the mapped image indeed seems to show the double nature of the basin (see post #137) in a way that is reasonably consistent with my mapping of the July 8 imagery (thanks again Ian), the Voyager imagery, and the other Oct 2004 imagery. I think there are enough matching features between the various images (best seen when mapped individually and blinked) to show a good enough solution. The shadowing effects with the new crescent image are also pretty dramatic.
Here's a look at the current map in progress:
http://laps.noaa.gov/albers/sos/saturn/iapetus/iapetus_rgb_cyl_070717b.jpg
I still have a bit of a shift to clean up in the longitude of Hamon (around 1.7 degrees) between the July 8 imagery and the Voyager image. However I think this wouldn't change the overall picture of the basin(s) since it/they are quite a bit larger.
New Iapetus article on the Cassini site:
http://saturn.jpl.nasa.gov/news/press-release-details.cfm?newsID=761
Apparently, it lived fast & died young...doesn't explain the dark patch, though.
It's from the rightmost image at this URL:
http://photojournal.jpl.nasa.gov/catalog/PIA06145
The face may be more challenging to pick out though due to foreshortening near the limb. Iapetus, yes full of mysteries
Hi once again,
http://saturn.jpl.nasa.gov/multimedia/images/raw/raw-images-details.cfm?feiImageID=116204 has been published:
Date: 2007-07-16
Distance: 3,239,597 km
Filters: CL1 and CL2
2x enlarged
Bye.
When this orbit's long-range full-disk sequence of Iapetus images is done, sombody should take the sequence and turn it into a little movie.
Greetings,
I thought I'd show a blinking GIF that helps illustrate the correspondence in features that I'm using in the map. There are three images, one is the full map I showed earlier, one subtracts out the Oct 2004 crescent image, and the third image has just the July 8 image from Ian. My take is that features line up rather well in BOTH eastern rims of the basin(s), as well as elsewhere. The fit between various images is generally around 2 degrees or better. I'll try and see if I can figure out how to annotate some of them (though I'll probably never get as good as T/A at that ).
http://laps.noaa.gov/albers/sos/saturn/iapetus/iapetus_blink_map.gif
It seems that there are indeed two overlaping big basins in south Roncevaux !
Marc.
Yes, I must admit that the more I look at this the more I find the basins (or basin rims) case to be compelling.
Something else I'm noticing today is that the area to the west of the Voyager mountains looks interesting, with the western extension of the peaks having a more continuous and wavy look.
http://laps.noaa.gov/albers/sos/saturn/iapetus/iapetus_rgb_cyl_070717b.jpg
Greetings T-A,
Good questions worth considering given the strange (or perhaps mysterious) appearance. For the wavy extension of the Voyager mountains, the original Voyager imagery had a somewhat similar appearance. I had at the time dismissed this as an artifact of the low resolution and being near the limb. The fact that the wavy appearance looks similar with higher resolution and less foreshortening (with Cassini - at least in the western portion of this feature as we move away from the limb) makes me think it is more real and therefore more intriguing. On the other hand the eastern portion of this feature in the original image is very near the limb and may be distorted in the map due to the higher elevation (a la mountain/bellyband extension). This is visible as a protuberance in the limb when I zoom way in on the http://photojournal.jpl.nasa.gov/catalog/PIA06145. The Voyager image is also being mapped for part of this feature so you're right that this is a puzzle. Hopefully we'll see how this jives with the much better imagery planned for September.
The whole region at the western terminus of the "wave" is somewhat chaotic (like things were stirred up somehow) and after all is at the base of the "dark triangle" . Note also that I updated the map on 7/25 to clean up the region in question compared to the version you are showing.
The wavy appearance of the easternmost basin rim is somewhat affected by foreshortening. I believe it is real however as evidenced in the blinking GIF (post #149) comparing two of the October 2004 images, as well as the latest version of my map online where you can see the matching rim features in how the two images are superimposed. The rim top features in the lower sun angle image match very nicely with the shadows inside the rim in the higher solar elevation (thinner crescent) image. The current map version is at this URL:
http://laps.noaa.gov/albers/sos/sos.html#IAPETUS
I kept trying to convince myself that traces of "white" extending eastwards from the end of Cassini Regio past the big crater toward the white mountains at the west end of the Regio were a continuation of the belly band. I still see little or no real "EVIDENCE" in the saturnlit part of that scene, but keep seeing disconnected blurry traces of white parallel to the equator in that area. The new image data, horribly blurry as they are, really do seem to show that the white-mountains or some other expression of the belly band do extend westwards into that area. This implies that the bellyband is essentially continuous, though it may have been trashed in places by later craters, like by that big basin in eastern Cassini R.
Just a quick look tonight at Where is Cassini Now? looks like that Iapetus will appear to go directly behind Saturn as seen from Cassini. Granted that Iapetus is about as far away as it can get, any chances for some imaging of this event?
Here's another movie of an "ancient" Cassini flyby of the moon. Sixteen stretched color frames taken between 2005-03-14 and 2005-03-30 were processed to better approximate natural color. Closest approach was around 1.3 million km. Magnified 2x. No new terrain visible, it shows the hemisphere Cassini saw over and over and over again, but I like movies so...
http://m1.freeshare.us/view/?163fs256963.gif
Edit: there's a bit of a stereo effect to be had, seen here between the 1st and 3rd image in both a cross-eye stereogram and color anaglyph:
http://m1.freeshare.us/view/?163fs290327.png
http://m1.freeshare.us/view/?163fs290043.png
Awesome! Gordan, you're a machine!
Hi,
let me just mention these three Iapetus far distance pics:
Btw., 9 additional far distance pics - including 3 showing Iapetus and Saturn - were updated on the http://saturn.jpl.nasa.gov/multimedia/images/raw/index.cfm.
Use 'Target Iapetus' for searching.
Bye.
Neat to see how things are setting up as we have 3 days or so until Cassini is farthest from Iapetus. During the next month we'll see the sunset terminator move from the eastern side of Cassini Regio to the western side as we transition from a gibbous to a crescent phase, as seen in this movie.
iapetus11.avi ( 291K )
: 292
We're closing in on Iapetus!
Images from yesterday are up!
There's a rather neat "zero" phase observation from September 9, 2006 at the PDS. Here's an animation of 10 clear filter frames showing the opposition effect (click to enlarge):
http://i108.photobucket.com/albums/n15/ugordan/Zero-Phase-Clear.gif
And an IR3/GRN/UV3 color version of 5 frames around the time of lowest phase:
Both are magnified 2x.
If you notice carefully, Cassini Regio doesn't show as big an effect as Roncevaux Terra does. What could that imply about surface characteristics? Coarser grained stuff in CR?
Or would the grainier (snowy) material be in Roncevaux Terra with more small shadowed areas between grains that help contribute to the opposition effect? I would surmise then that CR is less granular, perhaps more tarry or something. The actual size of the grains may be less important in deciding whether there's an opposition effect.
It's quite possible, I was just trying to spark some discussion. Zero phase behavior difference seen here could be pretty interesting. I'm not acquainted with photometry and backscattering properties of different materials. My comment was based on the fact powdery surfaces (very beaten up regolith) seem to show the strongest opposition effect. It could just as well be dependant on the specific materials. The shadowing effect is only a part of the equation, coherent backscatter (if that's what it's called) is I think more important at zero phase. These shots seem to suggest CR shows very little of that effect.
Gordan - these are interesting animations that you put together, and yes there are several factors that can contribute to the opposition effect. I think there was a post (by edstrick) mentioning the morphology of some features in Roncevaux Terra suggesting grainy snow, so the opposition effect may lend more support for this. He also suggested the dark terrain was granular though.
I wonder whether there is more of an opposition effect on the bright side of Iapetus compared with other icy satellites? There is a general discussion by Sanna Kaasalainen in this thesis, particularly in section 1.4.3 where Anne Verbischer is mentioned:
https://oa.doria.fi/bitstream/handle/10024/2893/backscat.pdf?sequence=1
And this paper might be interesting to read if I had a subscription:
http://pubs.nrc-cnrc.gc.ca/cgi-bin/rp/rp2_abst_e?cjp_p02-119_81_ns_nf_cjp
Beyond that, this gives me something to look for when walking around during the upcoming winter days.
Interesting PDF from a glance, thanks for the link. Regarding other icy moons, as far as I can see this is by far the lowest phase observation of any moon yet by Cassini (around 0.05 degrees minimum at disc center, comparable to the apparent angular diameter of the moon, 1.5'). I know there were some other low phase moon observations - Rhea comes to mind, but it was nowhere near this low a phase. Cassini did observe the rings at zero phase quite often, though. Earth-based observations such as the recent one are more favorable for catching several moons at the same time, but Cassini has the benefit of actually resolving the moons into discs.
Personally, I don't think Roncevaux Terra can come anywhere near Enceladus when it comes to the opposition surge. It's fairly bright albedo ice (comparable to Europa IIRC), but you can't beat the shiniest object in this stellar neighborhood. It might be interesting to compare it to Rhea on the other hand - similar albedos, but Rhea appears to be slightly dirtier.
Interesting. I would expect ice deposited as frost in a near vacuum to be very pure (hence bright), and in very small particles (hence high opposition surge) wherever it happened to be located. If Roncevaux is both less bright and shows less opposition surge than Enceladus I'd be inclined to attribute the differences to radiation damage rather than 'dirt' as such. That would be consistent with a very much lower deposition rate on Iapetus than on Enceladus - not unreasonable.
Below images from 17, 19 and 23 september together with simulated views (using Steve Albers' maps)
Nice views that you put together CAP-Team. One thing I'm working on is to try and soften the image edge on the map near the terminator in the vicinity of the central meridian in these views. One minor suggestion on the presentation would be to consider rotating the Celestia views (with certain keyboard controls) to match the orientation more closely.
It's interesting to backtrack to what we were looking at with the http://www.unmannedspaceflight.com/index.php?act=attach&type=post&id=11168 (Harkeppler in post #138) from a similar vantage point. For example the dark escarpment on the eastern rim of the western Claude basin was visible in those images.
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