RAW TRANSCRIPT -- NOT YET REVIEWED FOR CORRECTIONS BY CASSINI PERSONNEL

**FTF-NASA (US)**

**Moderator: Trina Ray**

**October 29, 2007**

**1:00 pm CT**

Man: Pass code is 3832523. Customer is NASA. Moderator of the call is
Ms. Trina Ray, scheduled for Tuesday, October 30, 2007 at 1:00 PM
Central Time. The ID is 1865320.

Man: Welcome and thank you for standing by. At this time, I'd like
inform all parties that today's conference call is being recorded. If
you have any objections, you may disconnect at this time.

And now, I turn this conference call with Ms. Trina Ray. You may begin.

Trina Ray: Thank you.

Well, welcome everyone to the CHARM telecom for October, "Probing the
Mysteries of Iapetus."

This is a really, really exciting presentation that we have for you
today. We had just an absolutely fabulous targeted Iapetus flyby just, I
guess, over a month ago or so. And very, very exciting one of the only
times that we'll see this body in the mission and the extended mission.
So it was very exciting and we have really a terrific set of scientists
who are joining us here today. The presentation is online at its normal
spot at saturn.jpl.nasa.gov, and we will probably go to full two hours,
I would suspect having five scientists online. And with we'll turn it
over to -- you're first, Amanda or...?

(Amanda): Yes, I'll give a brief into to the Iapetus situation.

Trina Ray: Okay.

(Amanda): And before we get into the results from this flyby. Right. So
on page 2, I'll go ahead and jump in here with what we knew about
Iapetus going into the September 2007 flyby. We have known for a long
time since the discovery of Iapetus, in fact, that it has this really
dramatic albedo dichotomy. So one hemisphere is very dark and one
hemisphere is quite bright, and it's the leading hemisphere that is
dark. And that is because Iapetus is tightly locked so the one
hemisphere is always taking the same direction, and that's the
hemisphere that stays in the direction of motion in the Iapetus' orbit.
And that's the very dark one, and nobody's known and a lot of theories
have been floating around about why that one hemisphere will be so dark
and the other is so bright.

And I think, especially Tillman is going to talk more about some of
these different theories in his sections. I won't go into the different
theories too much right now, but basically the big two theories with
that is either it's exogenic - it's coming in from some external source
and coating on the surface, coating the leading hemisphere \-- or it's
endogenic, so it is somehow coming from within the Iapetus, and being
emplaced from within by some geologic process.

So just in general the Iapetus, it's the third largest moon of Saturn,
and as I mentioned, it's tightly locked. The orbital periods -- orbits
way out past hyperion and the orbital period is about 79 days and so,
and that's pretty slow, and that ends up being a very important detail
here. More about from (John Spencer).

So the flyby that we're going to be mostly talking about today happened
on September 10 and that was out targeted flyby. But we did have a flyby
of Iapetus that was more distant and it wasn't an officially a targeted
flyby. Back on December 31, 2004 and that was at about 123,000 km
altitude which is still pretty good. I mean it's definitely still much
closer than we've gotten other than this targeted flyby. And it gave us
a really good view of that dark leading hemisphere, that low albedo
leading hemisphere and also the bright north polar region of the leading
hemisphere.

On the next slide, page 3, you can see some of the key images that came
out of that flyby and the really good views that we've got of this
equatorial ridge which were hinted at. The ridges were hinted at in
Voyager images but this has really illuminated the presence of this
equatorial ridge that's within the dark terrain on that leading
hemisphere right at the equator. And closer up images of that north
polar region really sort of display this pattern that is really
consistent with ballistic emplacement of dark material from some
external source and this is shown through this sort of streaky pattern
that's seen.

And bright rims of craters that are facing the north polar direction, so
they're in the sort of protective zone where if the dark material is
coming in from outside, then maybe those would be zones where you
wouldn't expect a material to land.

So on the next slide, what we're saying here is that -- okay, so maybe
this stuff is exogenic, but there is more to the story , and that's --
this is really what we're learning from this recent targeted flyby. The
flyby in September was inbound over the unilluminated low albedo
hemisphere, and so this is a really good opportunity to do radar
imaging. And in particular, we've got very good views of the bright dark
boundary on the anti-Saturnian hemisphere, and so this is another
opportunity to really see what the relationship between the dark and
bright terrain, and it can give us more clues about what's going on and
why the dark material is there and where it might be coming from.

And of course, we also got really good equatorial ridge views because it
was the path had its closes approach over a very low latitude near the
equator and again on that anti-Saturnian boundary region. So what we're
finding is that thermal segregation is very important, and (John
Spencer) is going to talk about that next. And then we'll have imaging
results from Tillman Denk and John will then talk about the serious
results. (Roger Clark) will talk about (unintelligible). I'll come back
and talk about the (unintelligible) results. And then we'll have (Steve
Auster) talking about the really interesting radar.

So why don't we go to (John Spencer) now for page 5?

(John Spencer): Okay. Thanks, Amanda. Can everyone hear me okay?

(Amanda): Yup.

(John Spencer): All right. So I'm to just say a little bit sort of a
theoretical introduction as to what thermal segregation is and why we
think it's important on Iapetus and explains quite a lot of what we see
in the images in the other data that we've got.

So on slide number 6 that's entitled, "Ice Sublimation on Iapetus." All
of Saturn's moons, you think have ice on their surfaces, I'm not sure
about Titan, but does probably does too, and think they're pretty cold
at Saturn's difference from the Sun, and so on most of the moons, the
ice is really hard frozen. And it acts like a rock and really there's
not very much happens to it. But Iapetus is an exception as its surface
can get pretty warm compared to the other moons for two reasons really.
One is that it's a very dark surface which absorbs most incoming
sunlight.

Yikes, excuse me.

And the other reason is that Iapetus rotates very slowly and that means
that the surface has a lot of time to heat up during the day. And so you
get dark terrains on other moons like Phoebe for example but don't get
nearly as warm as Iapetus because Phoebe rotates a lot faster and it
doesn't get as warm during the day. And so an Iapetus crossed the
critical threshold where ice becomes mobile; it can mobile. It can
evaporate, or technically we say sublime because that's the technical
term for ice that turns from solid to a vapor without melting first.
(Unintelligible) to evaporation. And once it evaporates, it can rise off
the surface and fall down somewhere else and move around and that can
happen on a global scale.

So the next slide, which I guess on slide 7 now, that talks about
localized movement of thermal segregation which is really a very simple
process. And it's one I've been thinking about for a long time and the
figure her is from I can assume my dissertation from 1987, and it's
really just -- it's kind of instability where if you have a (dirty iced)
surface under any kind of temperature variation on the surface that
could be due to some areas being a little bit darker than other or some
areas being a little shadier than others, any kind of discrepancy in
terms of temperatures, you're going to get this discrepancy in
evaporation rate because the ice is going to evaporate faster. And I say
evaporate, you're going to get the ice evaporating and the dirt is just
left behind on the surface. And so the evaporation darkened surface
makes it warmer that increases the evaporation and in the same way any
region that is brighter than average is going to get more ice falling
down on its surface that it can evaporate itself, and it's going to
accumulate ice so cooler regions tend to get dried when they get cooler
still. And it's a runaway process and eventually, you get to the point
where the regions that were originally a little bit darker now are
completely dark. They're completely covered in -- there's not ice at all
and they're very warm and then the regions that were a little bit
colder, now are covered in fresh ice and are much brighter and colder
still. So the surface just automatically sorts itself out into bright
and dark terrain.

This is just a theoretical idea in 1987, but when we flew past Jupiter's
moons with the Galileo spacecraft in the 1990s, this is now on the next
slide, I guess we're going to slide number 8 now. Then we saw that
indeed they substituted that (unintelligible) would appear to be thermal
segregation. So this is a close up picture of Callisto seen on the
Galileo orbit. And most of the surface is very dark and appears not to
have any water ice. And this (unintelligible) covered in an at least
thin layer of -- detecting the ice underneath from sublimation.

And then scattered across the surface from the top scalable in this case
bright regions where all the ice that's evaporated has condensed and
this comes straight to everything inside the blackhole white and not
much of anything and between. And I'd tell (unintelligible). This seems
to have happened on Iapetus as well.

But this is just local movement of ice, but this will happen on a global
scale as well particularly on Iapetus where the gravity is relatively
love and water molecules that evaporate on the surface can go hundreds
of kilometers before they condense again so ice can move around quite
rapidly on the surface.

And the next slide, slide number 9, shows the model that I produced a
couple of years ago. To explain the results from the first flyby of
Iapetus that (Amanda) was talking about, there we noticed that Iapetus
is not a simple case of a bright hemisphere and a dark hemisphere. The
arrows on text have gotten a little out of alignment here, but the copy
mid showed what will happen if Iapetus were simply through a cloud of
dark material and the side that face (unintelligible) and the opposite
would stay bright and you get that simple two-tone appearance in that
top right figure.

But things aren't so simple on Iapetus. The actual Iapetus, the bright
material extends over the poles and the dark material extends around the
equator, so instead of having two simple hemispheres, it's like the two
-- it's almost like the seam in a tennis ball where you have the bright
stuff wrapping around the or from the dark stuff wrapping around
equator. And this is something that can be explained by thermal ice
migration, and after we came up with model and after the last flyby, we
got some email from (Mendez) who was researcher back in the 1970s and
here I thought of this -- back in 1974, indeed there was an abstract
published by (unintelligible) of thermal sublimation of ice on Iapetus
could be possibly an explanation for its appearance. So this is not a
new idea, but we've developed it in more detail.

Now the next slide shows how I tested this idea quantitatively and so I
had a simple model where I assumed that the Iapetus is covered in ice.
But then you darken the leading side, the side that faces forward and
(unintelligible) by in-falling dark material. And so then the ice can
evaporate and recondense elsewhere and you track where all the molecules
go. And in this model, I assumed that evaporation shut off when just
about a millimeter value evaporated or sublime. And this could be
because you've exhausted the ice layer on the skin.

And so next few slides, starting on slide number 11, just show how this
model would work. There's a bunch of panels here, they're the main ones
to pay attention to though to talk to. Each of which is a map of
Iapetus, with latitude and longitude and the one on the left shows a
thickness of frost. This is at the beginning of the model where you're
having a uniform thickness of frost everywhere so every new thing looks
kind of grey.

And then the upper right mark shows the albedo where we have a
dark-leading hemisphere centered at 90 degrees longitude in the bright
streaming hemispheres centered at 270 degrees. Well this is the setup.
Maybe other parts simply a slightest (unintelligible) across from pole
to pole or along the equator show the thickness of the frost as the
model progresses.

Slide number 12 shows that in a very short time because the ice is dark
and can evaporate pretty easily in only 60,000 years. You started to
burn off the dark ice from the leading side centered on 90 longitude.
(Unintelligible) produced a bad patch but we could just cover it in the
\-- and as you progress by number 13,14,15, which gets up to 50 million
years. You can see that dark area expanding. The ice is reconventing the
other pole. It's making the pole brighter and what is expanding more
along the equator because of course it's warmer than it is towards the
pole. So you're getting this oval, dark patch but is gradually growing.
By the time you get to 90 million years or 89.92 in this exact
simulation on line number 16.

You're starting to evaporate a little bit of ice from the equatorial
region on the leading side as well. And when you compare this albedo
pattern in the upper right to the actual map of Iapetus in the lower
right you see was actually pretty I can -- we product the distribution
the bright and dark terrain on Iapetus. So this was a clue even by -
before the latest flyby that indeed temperatures and the migration of
ice around the surface was pretty important on Iapetus and control in
terms of what was happening there.

And you noticed, I don't show any images beyond the 89 millimeters. We
run the model further. And beyond that point, the model stops looking
like Iapetus because of the ice disappears from low latitude on the
training side as well around 270 degrees longitude, and that has not
happened on Iapetus.

And I think that's what - what\'s that telling us is that the process
that's happening is happening - things are being renewed, more ice is
being added to the system, maybe being dug up from underneath by impact
or something like that to replenish the ice on about 100-mill year time
scale, so things reaches sort of equilibrium over that time scale.

So but that's kind of only we don't have an exact model of that. But run
through this point, the model works very well. So that's what I showed.

And the next slide, Number 17 is just a conclusion from this part of the
talk saying that we think ice migration is important on Iapetus both
because we see local - some of segregation as demo will show. And we -
because of the shape of the light, dark boundaries much very well will
buy this kind of model.

And because of this (unintelligible), one of the predictions from this
model is that there is no ice at all in the dark terrain, it's just too
warm and it\'s completely evaporated from those regions and that's
something we can test using (unintelligible).

And so, I\'ll come back in a little while and I\'ll talk about the
temperature measurements we actually got and how they compared to this
model. But that's it from me for now and I guess Tilmann is going to
tell you about the images next.

Tilmann Denk: Okay. Hey, Trina.

Trina Ray: Yeah. We can hear you know, (Thomas).

Tilmann Denk: Thank you. Okay.

Okay. Good morning and many thanks for joining us. My name is Tilmann
Denk and I\'m working at a quiet University in Berlin in Germany. And
one of my major tasks in the past was imaging observation, planning of
the recent Iapetus flyby and just the data enhance now, I have to find
out what it all means what we can see there and this is still at the
beginning, but I will tell you a little bit about the process that we
have done so far.

Let\'s go to view graph 20 now, title trailing side of Iapetus. It shows
a 15-panel mosaic of the trailing side of Iapetus. The big base in the
south that you can see there is about 480 kilometers in diameter and
this is almost the size of the moon Enceladus.

Big basins are quite common on Iapetus. In this case here on the
trailing site, a very unusual property is in addition, that an older
basin of similar size has been partly destroyed by a later impact.

And immediately west of these two basins, there\'s an area with an
unusual (unintelligible) texture. It might be possible that this was
formed by the impact itself. Then going further north towards this
terminator, we can see some tectonic structure, several linear features
might be related to large impacts, but this has to be studied in detail
before we can say something conclusive here.

In the right or eastern part of the image, the dark-bright transition
terrain is visible very clearly. We knew from previous low resolution
data that this is a really complex area, but in the new images, it looks
even more complicated that we thought it is.

Near the equator, we see lots of dark flow craters and interesting, this
piece can be detected all around Iapetus (globe) at low latitude. So
there is this effect that (John) has just described that his model does
not described very well is at least in some parts be visible.

To the very east reach can be seen in the dark terrain while rising
behind the horizon and the bright, what's just left of the reach our
mountains, this bright area the has already been recognized in Voyager
data.

So let\'s go to the next view graph.

This is Number 21. The equatorial reach as seen in New Year's Eve 2005
data just to the right and in the most recent high phase images.

The Letter A as you can see in both (index) indicates an identical
location and you can also see this in the next view graph, 22. Here,
our - we used from the right angle camera taking in the 40 minutes
before closest approach. The letter indicates areas in the picture and
the resolution is about 300 meters per pixel in the very left frame and
about 100 meters in the right one, northeast to the right for all three
and rest is up here.

The reach more quality changes this longitude further to the east. This
is the left image between the Letters A and B. The roof of the reach
looks very flat while it changes into a sharp ring just west of the
position B or a little bit up of the letter B. It also changes into
isolated mountains there instead of a continuous reach as it is before.

Two of them appear quite tall of these isolated mountains then only a
few rather flat ones follow up to the large mountain visible in extra
horizon of the middle image. Here, the top ring looks again different.
Its shape appears now more rounded.

Then view graph 23, this should be a movie. Unfortunately, it\'s not one
in the PDF. So we have to skip that. Let\'s go to 24.

This view graph shows this area, again, back from the other direction.
West is now thought bottom and east is up the arrow. The red arrow shows
the mountain labeled C in the earlier view graph and the continuous
reach is now visible at the horizon and the mountain just the bright
west on flank - flanks in the center of the image is the one that was
visible at the (limp) in the middle image in the view graph 22.

So next view graph, 25, this is the eastern most of a group of mountains
that you have already recognized in (Y22) data. The top right full cloak
image is the whiter image that shows the mountains at the (limp) and the
arrow show the viewing directions of the new Cassini images.

The blue one, the blue arrow shows the west most view at a high face
angle. That's the right image. The yellow arrow shows a (yellow) phase,
more an (ADR) looking view. That's the image at the left. From the
whiter images, we believe that the mountains are fully bright but
Cassini base are showing out that only the rest on flanks have bright
patches and the major part of the surface of the mountains - of these
mountains that we are detected in a whiter data are still dark.

Next view graph, 26. I would ask the equatorial reach proceed on the
trailing site in the western direction. This was one of the main
questions for the flyby and we knew that a few bright mountains are
located near the center of the entire set on point. You can see the
circles - the right three circles there correlated to mountains that we
have known that exist. And that the Cassini data now, especially the
stereo data, this means this data of the same terrain taken from
different viewing directions to allow three angulation and the
production of digital terrain models.

With such, data we can now see that these isolated mountains extend at
low - at least costs 245 degrees longitude, so there are at least four
more such mountains.

Direct cross shows the center of the trailing site. This is point of the
surface located exactly opposite to the direction of motion of Iapetus.
And there is still a small area - about 300 kilometers wide where we do
not know so far if the reach of mountains extends in this area because
we do not have stereo data for this area.

So that to the west, become closer to the terminator and there\'s no
indication of unusual equatorial mountains in this region.

Next one, 27.

This extent of a reach can be traced over about 70 degrees around
Iapetus' circumference. The appearance of the reach around the whole
slope shows that this view graph, Number 27, here, you can see where we
have an equatorial reach on Iapetus and where it is missing.

The green bar shows that the reach or at least isolated mountains are
there. The red bar shows extent of reach of mountains. There are areas
like between about 340 degrees west and 50 degrees west where one can
argue that an ancient reach might have been destroyed by a giant impact.

But in other areas like between 270 and 330 degrees west in particular,
there\'s no obvious large impact structure visible. And so, this means
that our tentative answer of the question, is the reach ever spent fully
around Iapetus cloak, is we don't know yet. But maybe we can find out.

Then the next view graph, 28, dark and bright. This is often important
topic on Iapetus and the new images show almost no gray areas, only
either dark or bright areas. This is suggestive that the process that
creates the dark (blanket) must be very efficient in removing or
covering the bright ice and for me, this is one of the major reasons why
I believe that John Spencer's model with this thermal segregation is
really an important one for the surface of Iapetus.

Next one, 29.

The equator was facing slopes about at least as low latitude. And
whenever you look in this image, most of the dark terrain is correlated
with slopes that are facing to the left and to left is to the equator in
this case.

It is also very interesting that the amount of dark terrain is reduced
to further south - the further south we go. This is another indicator
that a thermal effect plays a significant role on the surface of
Iapetus. So the closer to the (unintelligible) it isn\'t the left dark
material is visible on the surface.

Then the next number, 30, as mentioned before, (unintelligible) this
behavior of (unintelligible) dark slopes were already obtained in data
of the 2004 non-targeted flyby. And there, you can also see some
(striation) in the upper image, but this is actually an illusion.

This is not really a true surface property. This is an illumination
effect that indicates that there is maybe the material coming from an
area closer to the equator. But actually, this is - the illumination,
you can always see the dark shadow then the bright crater flow and then
the brownish greater (rim patent) and this points exactly to the sun. So
we have always the same brightness (patent) view in the crater and this
is indicative also that it\'s always - the equator was facing slope that
(unintelligible) and in the bottom picture, you can see that the bright
rims are facing to the pole.

Then the next one is 31, bright spots in the dark terrain. This is not a
topic that we want to explore with the imaging data. What we - we
searched for them already in the 2004 data where we had about 800 meters
per pixel spatial resolution and to be - we could not see any obvious
bright (ejector) in this dark terrain. So this means we couldn't find
any bright hole down to about half a kilometer in size. The (index)
shows about 4-kilometer space resolution and today you can also see that
at the equatorial area. There\'s no dark - bright spots in the dark
terrain and this is only visible at higher latitudes, but there again it
is the pole that's facing slopes of craters that show this property.

Then next, the view graph 32, in the data from the recent flyby, this
changed the spatial resolution down to about 10 meters per pixel. We
could see several bright spots and many bright craters that indicate
that's the darkening process is ongoing today. The bright object in here
is the most prominent that we have found, the corresponding crater is
about 60 meters in diameter. Since a 60-meter size crater is less than
10 meters deep, we can infer from these images that the dark layer
should not be - should be no more than a couple of meters thick.

Next one, 33, now I will switch to the global brightness dichotomy
question. This list shows my pre-Cassini view of the literature, and I
will not go through this in detail. This would take too much time. But
most attendance received the second group which assumes that a process
bringing in material from outside causes an alteration of the surface,
but none of these ideas that are listed here received fully acceptance.

Next one, 34, this view graph summarizes our current view following the
most recent flyby and it contains properties and processes more or less
unique to Iapetus and they are combination leads to the unique
brightness dichotomy.

We have first a synchronous rotation which gets the leading and the
trailing side. This is not uncommon for our satellites but for Iapetus,
it plays a significant role for the explanation of this brightness
dichotomy. Then second, we have a source of exogenic material that is
influencing the leading side but not really the trailing side. That's
possible due to the synchronous rotation. And what kind of source is
another question that is not directly related to Iapetus, but we can
assume that there is one and micro meteorites from interplanetary - from
the interplanetary space or my preferred version is that the outer moons
of Saturn are losing material and the richer crate moves - the material
from the retro crate moon is spiraling in and hitting Iapetus on the
leading side. These are two candidates.

Then third, the orbit of Iapetus is far out. And this is important
because it means that it\'s no big of obstacle like Titan that prevents
exogenic material to reach of the surface. This is off the case to
Hyperion but not for the other regular moon of Saturn like Rhea for
instance. If material from outside is spiraling in then Titan would seep
up everything before it can reach Reach or Dione or the other, you know,
moons.

The next view graph, 35, this should be an animation but was -
unfortunately, it\'s one in the PDF. It was only one in the PowerPoint.

((Crosstalk))

Woman: I hope we can go back and access the PowerPoint, you know, later
on and then so they can see the animation.

Tillman Denk: Okay. But that's not that bad. It shows just a different
brightness enhancement of the dark and bright terrain and how the color
of the dark and the bright terrains correlated to the location. And the
surface indeed appears that the 180 degrees and the 0 degrees Meridians,
these are those that separates the leading the trailing side of Iapetus
that these are also a separator for all the color. The leading side has
a radar and slightly darker color throughout the poles from - poles to
the equator down to the other pole while the trailing site's color is a
little bit more greenish, whatever this means in detail. And that was
detected in the data from the imaging system in the last two years and
that's very interesting because it provides a link between two theories
that will probably explain the brightness dichotomy.

Then the next one, the continuation of the last one, the (12) points,
the very flow rotation of Iapetus. This is also a key it allows us pass
of the surface to get a temperature that is higher than anywhere else in
the Saturnian system and as (John) already explained this - the thermal
segregation process can only act on Iapetus or it only acting in a
global way on Iapetus and one reason is because it rotates so slow and
this allows the sun to stay on the surface for a very long time or about
40 days almost and just allow the temperature to go unusually high. So
it\'s been very low for sensing but for the Saturninan system, it\'s
very high temperature.

And then the fifth one, the dark blank and it\'s very thin. This is -
you can see it from the imaging data from this bright crater, rays for
instance and other from radar data that (Steve Auster) will say anything
about in one of the next presentations. And then finally, the thermal
segregation as an acting process proposed.

Then you go to the next view graph then you can see the story that we
want to propose how the brightness dichotomy on Iapetus is formed. There
is some gas from (unintelligible). This was proposed earlier by
(unintelligible) in 1974 and (unintelligible) in 2002. She was extending
the idea that Phoebe is the delivery body to the other (outer side of)
lights what makes more sense because the color of Phoebe doesn't really
match although (unintelligible) will argue why this might not be a
problem.

And then this feather light dust does not cause the brightness
dichotomy. It was proposed earlier but it causes the color dichotomy
that was detected in the ISF data. And this color dichotomy - this is
triggering so to speak a symmetry between the leading and the trailing
sides that the model by (John Spencer) is requiring for the thermal
redistribution so that the thermal segregation is acting in a very
excessive way on the leading side but only on the - let\'s say minor way
especially near the equator and the bottom of the crater and especially
on the slopes that are facing to the equator on the trailing side. And
the (rec) 49 data from ISF insists in particular nicely support this
scenario.

Then the last view graph shows pictures of Saturn. We also made some
images where I was thinking about a planetarium directors that might
like to show on their - (to tell us) how Saturn might look from Iapetus
and therefore we took about 34 hours before the flyby this image of
Saturn and also in the next view graph, you can see an image of Iapetus
that was taken at the same time and the spacecraft was approaching over
the (unintelligible) hemisphere. Iapetus is still visible as a crescent
by effect and the moons are visible as almost full glow.

Okay. And there is still some information on locations that you can find
the data of course in the pictures - on the Web site of the Cassini
imaging team and cyclops.org but we at the Free University of Berlin. I
also want to advertise our Web site a little bit. We also compiled all
the images of Iapetus, and we also have a site that shows the planning
in detail.

Okay. That's it. Thank you.

Trina Ray: Thank you, Tillman. Were there any questions because
Tillman's going to have to go after his talk here.

Okay. Well, with that, we'll go on to Dr. (Roger Clark). (Roger), have
you joined us?

(Roger Clark): Yes.

Trina Ray: Wonderful. Take it away.

(Roger Clark): Okay.

Let\'s see. Slide 41 is the title slide, and we can rapidly move on to
slide 42 which tells a little bit about the VIMS instrument, a Visual
and Infrared Mapping Spectrometer. The VIMS is an imaging system, all
the images on this slide are taken with the VIMS, and the difference
between here than a standard camera is we're spatial resolution
challenged. So we only have 64x64 pixels, so we have to take lots of
frames and mosaic them together to build up a big image.

But our advantage is in every pixel and every image that we take, we get
352 wavelengths and we get those all at the same time. Whereas with,
like the ISS camera which has great spatial resolution, they have to
move filters into place to get multiple wavelengths.

So it\'s a trade between spatial and spectral, and spectral allows us to
get compositional information which you\'ll see.

The spatial resolution of VIMS is similar to what you can see with your
eye if you\'re slightly myopic like 20-30 vision. So the images that you
see - if you were standing on a spacecraft from VIMS, the images you
would see would be similar to what you could see if you were standing
there, you know, like in a spacesuit of course.

Okay. Let\'s go to the next slide and slide 43, and it shows mosaics of
our Iapetus data from the Rev 49 flyby in three difference wavelengths,
and these are all in the infrared and I\'ll explain a little bit the
wavelengths on the next slide when I show a spectrum. So your eyes see
about from .4 to .7 microns in wavelength. So they use wavelengths 1.8
microns or way beyond what your eye can see and beyond what color
infrared film can see also.

So the 1.8 microns reflectance shows of hue very similar to invisible
and there\'s an ISS frame Iapetus there on the left to show for
comparison. And the dark material is dark and the bright material, the
IC regions are bright at 1.8 microns. But as we move further into the
infrared and to the - closer to the 3 micron regions, so there\'s a 2.65
micron reflectance. There, the ice is getting darker and the dark
material is getting brighter and then as you move even further to the
infrared, you\'ll see at the lower left frame at 5 microns, the so
called dark material is actually bright and the ice is very dark. In
fact, in the 4 to 5 micron region, ice in general is darker than
charcoal, so it\'s really quite dark. And then the bright material is
here more light gray in color if you could see at those wavelengths. And
then in the lower right is just a color composite of that so you see the
relationship going on as a function of reflectance.

So if you have infrared eyes, you could see something like this in terms
of color. Let\'s go to the next slide, Slide 44.

So this is a typical spectrum that we see from the VIMS. And again, your
eyes see over there just very left most portion of the plot from .4 to
.7 micron to approximately \-- basically where you see that hump in the
blue spectrum which is called the Rayleigh Scattering Peak. And this
Rayleigh Scattering Peak is quite important and I\'ll get back to in a
minute. First, looking at the blue spectrum at 1 ½ and 2 microns, there
are two big deep absorption bends due to water, H2O ice and then we go
into a big 3 microns ice band and then out beyond 4 microns, you can see
how dark the ice is. It\'s way down there just on the very bottom
reflecting only a couple of percent reflectance. And charcoal like on a
grill is maybe 4-5% reflectance. So this is quite a bit darker than
charcoal.

Also seen there is CO2 in 4 ¼ microns and we're seeing CO2 throughout
the Saturn system mainly in the dark material but it may be in the ice
also. We also see CO2 in the Jupiter system. So there may be a
connection here and we're trying to work on that.

Working from a long wavelength shorter, the next exciting thing there is
CH. We see a tiny trace hint of some CH bond. These are organic
molecules and we have a paper and press on that and I\'ll give the
reference to that in a sec. Then a little bit shorter is NH3 with a
question mark. The reason why we have a question mark there is that
right of that wavelength, our instrument has a filter gap between order
sorting filters from a grading and that causes some funny effects
sometimes. So we have a little bit of uncertainty in our calibration.
However, as the Iapetus data has come in and we had a team meeting last
week, I think I convinced most people in our team that this is the real
feature and we're mapping a real feature on the surface and that's a big
advantage to an imaging spectrometer is that we can see what are
artifacts and what are real by not just the shape of the spectrum but
that were mapping real things on the surface. And this ammonia band maps
in the dark material all over Iapetus.

And moving shorter - the big broad thing there at 3 microns is due to a
combination of things there. There can be some ice in there. There could
be some bound water and this is the region where in water, the OH
stretch fundamental occurs. The O and H chemical bond is stretching at
that wavelength and NH and ammonia stretches in that region too. So
there could be ammonia bound to minerals that contributes to this band
and because it\'s all smashed together into one big broad envelope
there, we can separate them at this time.

At shorter wavelengths, we see a lot of little small weak pictures there
around 2 to 2-1/2 microns, and we're working what exactly those are
caused by. Typically, they\'re hydrogen related either in like OH or NH
bonds and we see these kinds of things in minerals a lot. So they\'re
not unusual but until we know the specific wavelengths or can identify a
specific compound to them, we can\'t say much more. But once we can, it
might tell us something about the chemistry going on.

What we can say is it\'s out of this world because we don't have
anything like this in our databases at the moment.

So then going back to the visible part of the spectrum where the
Rayleigh Scattering Peak is - this is interesting because Rayleigh
Scattering in surfaces was not recognized prior to 2007. So it\'s a
relatively new discovery of the effect and it has some interesting
implications for the Saturn system. And one is that you only need a
fraction of a way percent up to maybe a couple of way percent of very
fine particles distributed, you know, uniformly and widely throughout
the ice. And you need that small amount, if you get too much then the
particle get too close together on average and the Rayleigh effect goes
away.

So Rayleigh Scattering occurs when the particles that are causing the
scattering are much less than the wavelength of light. And since we're
working with 1/2 micron wavelength here, they have to be much smaller
than 1/2 a wavelength or 1/2 micron in wavelength.

So and the Earth's sky is blue because of scattering off of molecules.
So typically, Rayleigh scattering is caused by particles much, much
smaller than the wavelength in the case - in this case in the Earth's
atmosphere, molecular size particles. But you get the effect to some
degree as you approach the wavelength and then above the wavelength and
the effect will go away.

So this Rayleigh peak tells us that we have very fine particles in
extent at the surface layer of the ice. But we're seeing this variable
throughout the surface of Iapetus and variable amounts on other objects
as well. All the satellites were seen it including some in Saturn's ring
all the way out to Phoebe. We see it nicely on Dione. We see it nicely
on some of the small moons like Epimethius.

So it\'s fairly common in the Saturn system. And what this is telling us
is there this very fine grain dust coming in and coating the surfaces of
all of these objects and that's telling us it\'s external to these
bodies. Now, there\'s still could be some material that some dark
material that is endogenic to the bodies. But predominantly, what we're
seeing optically has to be the exogenic.

Back to those two micron features, we're seeing those throughout the
Saturn system and other bodies also. We see this strongly on Phoebe and
we see them on Dione We see it in the F-ring.

So the same composition that's causing this stuff even though we don't
know the exact composition because the absorption bands are the same, we
know the composition is the same.

So we have the same composition, we have the same Rayleigh scattering
effect going on throughout the Saturn system, implying that this dust is
coming in and coating all these objects. So the question is, where is it
coming from?

Well, let's go on just a little bit here and go to slide 45.

This just shows a blowup of the three micron regions and shows the very
weak absorption band we're seeing for the organic compounds, tracing out
fractions of a percent. And these kinds of compounds do exist in like
comets and in the interstellar medium, so these are not unusual
molecules by any means, but it's at least chemically interesting that
they're there. And PAHs stand for polycyclic aromatic hydrocarbons.

Next slide.

Oh, and that's - that PAH is in a (unintelligible) paper which I think
is online now.

Okay, so going to slide 46, shows a map of the different compounds that
we're seeing, the CO2 which you can see is mapped in red and the color
composite image, and that's predominantly in the dark regions. The
bright areas correlate with the green H2O ice and that's pretty obvious
I think, (unintelligible) and fairly clean ice.

And then the blue is showing the Rayleigh scattering strengths. And what
this image shows is that as you move away from the equator, the ice is
getting cleaner. And this - what this means is water molecules are being
driven from the equator toward the poles so that we're getting cleaner
ice. So it's covering up some of the dark - these fine dark (grants).
And that supports (John Spencer's) segregation model.

Let's go on to the next slide.

This just shows our high resolution view of Iapetus in the dark to light
transition zone, so you can see the interplay between the CO2 containing
dark material and the bright icy material.

And then along the equator there, that's a horizontal bend, you see the
bright, white mountain sticking up, and those are pure - more pure ice.

Let's go to the next slide. And this shows some of the effects that
we're seeing we don't fully understand, and that is the - this 2 micron
triplet, occurs in the dark material. And then as you move toward the
bright material, a little bit of ice, gets mixed in with the dark
material, so the further away from this transition zone, the less ice
there is. I think (UVIS) will show that they're seeing ice kind of
everywhere. And that may be in our big 3 micron band that we see
everywhere. Even the dark material has this 3 micron band. And so, yes,
there could be ice still in the darkest areas.

And as we get closer to the brightest areas, we get the strongest water
signature, and as this map shows, the ice bands are asymmetric and
they're asymmetric in a way that we don't yet understand. They're not
like laboratory ice that we produce here in the lab.

And we're seeing this asymmetry throughout the Saturn system, and it's
also seen in a couple of other places where there are good spectra, like
the uranium satellites have this asymmetric absorption also.

So it's telling us something we don't yet understand but we're working
on that problem. Something is happening to the ice structure is what
it's telling us.

Let's go to the next slide which shows the CO2. The CO2 occurs
throughout the Saturn system. Wherever we see the dark material, we get
the strongest signature of CO2. And the CO2 is band is moving around.
And we don't - we understand in principle why, but we can\'t say
specifically why yet. The CO2 is trapped and it's saying that's trapped
in different things for it to move around. This is pretty common on the
earth. Many minerals have CO2 trapped in them. And depending on the
bonding of the mineral, it will move the band around. So this is
actually telling us that there is some compositional variation that the
CO2 is being trapped into different things. And we're working on trying
to understand what those are right now.

Let's go to the next slide. And this shows the ammonia band and how it's
just a trace of less than the weight percent of ammonia condensed on
different compounds and laboratory reproduced the shape of the
absorption band that we're seeing. Strongly we see it on Phoebe, we see
it on Dione; we see it on Iapetus. We do not see it in F-ring which is
interesting. And then we've only gotten good, clean or relatively clean
signatures of dark material on those three objects \-- Phoebe, Dione,
and Iapetus. And they all have the same composition.

And then the next slide, slide 51, shows the distributions that we're
finding for the CO2, the ammonia, and the water-ice. Some of the trends
that we're seeing which we're trying to model now, and that is the CO2
is strongest at the transition zone, and as you move further into the
dark regions, the CO2 decreases a lot, and opposing that, as you move
further into the dark regions, the ammonia tends to increase. So we're
trying to figure out what that means and what they may mean for (John's)
sublimation model.

Okay, next slide, slide 52, is conclusions.

So this is what VIMS has detected and what we understand so far. So we
have beautiful signatures of water-ice and can map the water-ice. We
have the strongest signatures of CO2 that we've seen anywhere in the
Saturn system. We see variable positions of the CO2, showing that there
is compositional variability that we're trying to understand. We have
trace amounts of organics. We have trace amounts of ammonia. I think
that probably has become a little stronger in the last week as we\'ve
understood our instruments and this mapping of Iapetus has helped us to
understand that. And I think the band is becoming more accepted.

We have several unknowns for which we don't have any match to any
compounds in our terrestrial spectral databases. So we're trying to
synthesize compounds and trying to understand what these absorptions
are. And that's one of the nice things about spectroscopy. It can point
us in the direction and get us close so that with a little chemistry
work in the lab, hopefully we can find out the exact answer. But
sometimes it takes years to do that.

This Rayleigh scattering effect, I explained pretty well, the particle
must be very small and both in diameter and abundance on the surfaces.
So all of the surfaces where there's ice, there's very pure ice but not
completely pure. It's not as pure as freshly falling snow on the earth
for example.

So the - all of these things taken together, we see these same
compositions throughout the Saturn system, the Rayleigh scattering
effect. That's all implying that there's dust coming in from external
source to these satellites and that may mean that it's external to the
Saturn system or where, if it's not external to the Saturn system, where
might it be generated. And there's no clear evidence that it's generated
on all of the major moons. Could it be coming from one of the smaller
outer moons?

And with that, I'll stop.

Trina Ray: Okay. Do we have any questions right now before we go on to
(John)?

Okay. Let's go ahead and go on to the next presentation. (John), go
ahead.

(John Spencer): Okay. This will be fairly quick because I've already
kind of given you the bottom line that I will describe.

Now, the first look at the CIRS observations, that's the thermal
infrared observations by Iapetus that we got on the September flyby. So
this is the whole CIRS team here.

And first just a quick primer on blackbody radiation, how this allows us
to measure the temperature of something from a distance, so basically
anything that is warmer than absolute zero is emitting heat radiation.
And the wavelength and the intensity of the radiation are characteristic
of the temperature, and so here you have a picture of lava coming out of
a fracture on the lava flow. And when it's very hot, it's emitting
yellow light and red light and a lot of infrared light as well which you
don't see in the photo of course. But as it cools, you only get the red
light from the infrared light. As it's even cooler, you don't see any
light at all. The lava looks black. But if you put your hand up to it,
your hand can certainly feel the infrared heat radiation coming off that
lava and you could still, if you had infrared sense device, measure that
heat and measure the temperature.

So by looking in this red light, particularly for cool objects, we can
measure their temperatures.

And at the very low temperatures that we get in the Saturn system, the
wavelength where the heat radiation comes off is very long wavelength.
It's usually almost always too long a wavelength for (unintelligible)
VIMS instrument to detect. And so we have another instrument on Cassini
called the CIRS instrument which detects the longer wavelengths infrared
light and can detect the heat radiation.

So the next slide shows a picture of the CIRS instrument and this
describes briefly what it does. They're very sensitive to wavelengths
between 7 microns and 300 microns. And remember, VIMS is from 1 to 5
microns. So these very long wavelengths we can detect the heat radiation
from the cold objects in the Saturn system.

CIRS obtain spectra and not just a. measurement of the total amount of
the heat radiation which is very useful for Saturn and Titan to measure
their compositions but for solid objects in the Saturn system like
Saturns rings and the moons, we get some temperature information though,
you know, maybe we'll get some compositional information at some point.
But it's a lot more tricky to do that. For most we'll be looking at
temperatures.

The next slide recaps a previous flyby of Iapetus and the observations
we got with CIRS instrument. Now this is the New Year 2005 flyby. (So
over) there was the best observations we got out of spatial resolution
of about 35 km, that's the smallest thing we could see. And we saw
temperature is up to 130 Kelvin or - which is a whopping -225
Fahrenheit.

But that's pretty warm for Saturn, and that's what we got to thinking
about water migration on the surface of the Iapetus. But we didn't get a
look at the night side and really all most of our day side data are
proximal little bit in the other poles was of the dark terrain, but with
a pretty limited look. Do we are very anxious to get the data from the
flyby last September where we could look both the night side
temperatures and temperatures on both bright and dark terrain during the
day.

Well, the next slide shows a nighttime temperature map that we obtained
in the September flyby and here we got a really nice view of the night
side of. The temperature map in the lower right is showing temperatures
measured by our long wavelength part of our instrument. And this is the
wavelength between 20 and 200 microns. And temperatures are really
pretty uniform on the night side. It is between 50 and 55 Kelvin which
is pretty cold, but pretty uniform as the upper image shows. This is
superimposed with temperature and color information on the albedo data
from the imaging camera and shows that we are mostly looking at the dark
side here at night.

And so this was 130 Kelvin during the; it's only 55 Kelvin at night. So
it's cooling off very dramatically at night. And that means the surface
has to be very fluffy. It's really not very at retaining heat at all,
and in fact, the amount of fluffiness which was measured by something
called (thermal inertia), it's similar to the other Saturnian moons even
though this is a rather unusual surface. It has about that same kind of
texture and it's a very poor conductor of heat.

We do see some interesting anomalies on top of that. The green arrow
points to a region over on the right side which is distinctly warmer
than its surroundings, and this seems to be a region that's better at
maintaining heat through the night. And it's maybe a little bit less
fluffy than its surroundings, but who knows what's going on there.

The really high resolution data we got with of the day side under the
bright dark boundary, and the next slide shows a high resolution
noontime scan across the region where the bright and the dark terrain
are intermingled around midday.

And now our resolution is only 8 kilometers and we seem very large
variations in temperature in scan of the red rectangle in the right hand
panel shows where the scan is on the visible wavelength images, and you
can see a few good correspondence between the dark terrain warm
temperatures and the bright terrain and the cold temperature, so every
dark spot on the images then to a warm spot in the infrared scan.

And here we get peak temperatures a little bit of cool 128 Kelvin
compared to what we saw in the middle of the dark terrain on our flyby
two years ago. But in the bright terrain, the temperature's really
getting up to about 113 Kelvin, so that's pretty thing that scans
difference.

The next slide shows a blowup of the image and shows the size of our
field of view where we're measuring that one at 128 Kelvin. You see it's
almost completely, it is really completely on the dark terrain. So we
are getting a pure measurements of the dark terrain temperatures and
then similarly, our coldest temperature purely on the bright terrain. So
we have - thanks to thermal segregation that sorts these things out into
these very large patches of bright and dark, we can completely resolve
the temperatures of the two components.

And that's nice because that's allows us to calculate the rates which
ice should be subliming or evaporating from these surfaces because that
does depend on the temperature. And so from the bright terrain, it's 113
Kelvin. If you leave ice at that temperature or at that maximum daytime
temperature on the surface for a billion years, you'll only lose 10
centimeters of just 4 inches of ice. Anyway, not very much ice in that
much time, and in a billion years, you'll be able to mix the ice back in
or dig up more ice from the interior just by impacts on the surface. So
that's a pretty insignificant rate of evaporation.

But on the dark terrain, you'd lose 20 meters, 60 feet in a billion
years. And that's more than you could really put back to by any other
process and so you are going to lose ice from the dark material. It's
really not stable there. And so this is consistent with the thermal
segregation that we see that I talked about earlier: the bright
pole-facing slopes and the dark equator-facing slopes that Norman talked
about and the overall shape of the light dark boundary being controlled
by this evaporation of water.

And so just to conclude this, we've got nice direct measurements in
bright and dark terrain temperatures and in the bright terrain, the ice
is pretty stable in the dark terrain, it's highly unstable and we think
that explains a lot of what we see. And that's it from CIRS.

Trina Ray: Okay. Sounds good. Thank you very much (John).

Before we go on to Amanda, I just wanted to remind everyone regardless
of the capabilities of your phone, if you press star 6, you'll be muted.
It sounds there's somebody other who has a - (us on hold) - and if you
wanted to press star 6, you would be muted. With that, we'll go on to
Amanda.

Amanda: Okay. Great. So we're still on slide 62 and talking about UVIS
results from the Iapetus flyby. On slide 63, we briefly described the
ultraviolet imaging spectrograph, it's an imaging spectrometer. It had a
two-dimensional detector so there's 64 spatial pixels in one direction
and then the spectral dimension is in the other direction and so at any
time, we're getting a 1024 wavelength or a maximum of 1024 wavelength.

And then we can just scan the slit by using - by using the spacecraft to
make images. The far ultraviolet channel covers the wavelength range of
about 110 to about 190 nanometers and there are other spectral channels
incorporated in the UVIS instrument, but I won't be focusing on this
here in this presentation.

So again, the Iapetus observations that you visited during the September
flyby included a stellar occultation which I won't talk about too much
but we did do a stellar occultation where we watched a star pass behind
the rim of Iapetus to look for an attenuation of a starlight by any
atmosphere or gases that might be present and we did not see any
significant attenuation.

We'll be using those results to place upper limits on any gases around
the Iapetus but we don't see anything very significant. Most of our work
is focusing on surface reflectance measurements which we can use to map
out water-ice and also non-ice species and thereby sort of study the
thermal segregation that we think is happening on Iapetus as we've been
talking about.

So on the next slide, slide 64, is a plot that shows you what water-ice
looks like spectrally in the far ultraviolet and this is showing you
that it has a very strong, very significant absorption feature.
(Longward) of about 165 nanometers or 1600 Angstrom that water-ice is
very bright and even long word then it continues being bright through
the near UV and to the visible. But shortword of about 1650 Angstrom,
water-ice is very, very dark. And the wavelength of the absorption
feature is generally contingent on the grain size that is present. So we
can map out these absorption feature across the surfaces for any region
that we look at, we can sort of determine the strength of this
absorption band and use that to tell us about how much water-ice is
present.

Now, on the next slide, slide 65, we zoom in on that water-ice
absorption feature shown here now in red and compare it with the
reflectance spectra of other sort of candidate species, carbon and
(unintelligible), to show you how they looked in comparison. And to show
you that again the longer FUV wavelength, of course, water-ice is much
brighter, but at the shorter wavelength, the water-ice is so dark the
non-ice kind of primitive type materials are actually brighter than
water-ice. So again we can use this information to map out different
species.

The next slide shows you one of the results that we obtained on just a
sort of highlight this spectral reversal of water -ice and non-water-ice
stuff from the December 2004 or January of 2005 slide flyby.

Because water-ice get so dark at the shorter wavelengths and most
non-water-ice materials are brighter, we do see the spectral reversals
and this is shown by comparing these three images at the bottom where
the ISS digital wavelength images shown over on the right.

And then the alignment alpha image at short (SEV) wavelength that's
shown in the middle, and this shows you that the bright pole is actually
darker than the lower latitudes on that leading hemisphere there that
are visibly dark. So there's a spectral reversal that we see, which is
just kind of an interesting thing.

Now, on slide 67, I'm showing you one of the images that we obtained on
this recent flyby and you can see that the spectral coverage spectral
resolution has barely increased from that map that we've obtained on the
previous flyby.

And here, this is a scan that we did of the boundary region, the light
dark boundary region on the anti-Saturnian hemisphere and at this
resolution, we can detect those bright voyager mountains that are shown.
You can kind of put them out in this red and blue pot here at the top
that show up as blue which tells us that they're relatively high in
water-ice and generally we are finding that water-ice concentration is
going to be pretty well-correlated with the bright areas as (Roger) also
mentioned from his results too from VIMS.

But we can also even detect kind of vaguely this that very big crater
was in the bright terrain down towards the lower left. And we can use
these types of maps along with higher resolution spectral information to
try to understand how water-ice content is varying across the surface
and how the spectrum of the non-water-ice stuff is varying too.

Let's see. And then I also wanted to mention here that in this image
here, it's a three-color composite. So the bluish reddish - or
bluish-greenish tells you about basically reflected so well which is
greater or brighter when there's a lot of water-ice.

And the red is the alignment alpha wavelengths and that's a shorter
wavelengths and the sky is bright at alignment alpha because of the
interplanetary hydrogen and the Saturn system hydrogen too.

But interestingly, also that the dark terrain on Iapetus is relatively
bright alignment alpha because of the spectral reversal again. And the -
and so, actually, it turns out that if you were alien with UV vision or
whatever, flying around Iapetus you might have to be careful not to
crash into that dark material at the (lim) there because you cannot see
the (lim).

Okay, on the next slide though, we pull out from that three-color
composite, we've just looked at the longer wave lengths to try to get at
a water-ice map, just by doing a simple correction for incidence
(single) right now, solar incidence.

And again, we can see that this bright Voyager mountains seem to be
relatively high in water-ice and generally, again, we see a pretty good
correlation with bright material being greater \-- richer and pure
water-ice.

So on the next slide, slide 69, this is where we're starting to pull out
UV spectra of particular regions on the surface to look for color
variations and to for water-ice variations either within the bright
terrains or within the low albedo terrain to look at volatile migration
and to look at the distribution of the non-ice stuff.

And so some of the dark regions that we've looked at here are labeled
with red boxes numbered by 1, 2, 3. The larger box Number 1 was an area
that we got a good spectrum of in the last flyby in December of '04 and
then 2 and 3 are just some almost randomly picked regions just to
compare with 1.

And\...

Trina Ray: (Amanda) is the width or height of that box, is that your
slit height or length? Is that\...

(Amanda): No, actually.

Trina Ray: Okay.

(Amanda): It's - what do we do here? No, the slit in 1 and remember the
slit is long and skinny.

Trina Ray: Right.

(Amanda): So it would be square anyway. It could be if we did a scan.

Trina Ray: Yeah, I was thinking the scanner\...

(Amanda): But from 1, from that earlier flyby, the split was bigger and
so we just took a few central pixels for the mouth to get a spectrum of
this area here.

Trina Ray: Oh, okay. Okay, I see what you are saying then.

(Amanda): And in 2 and 3, it's closer. It's much closer and so the
spatial resolution was a lot better but still I think that the - I cant
remember, off the top of my head exactly like relatively how big the
slit was but I think we've pulled out central several rows to isolate
different types of terrains.

Trina Ray: Okay, thanks.

(Amanda): And - but before I go on, actually, we also then compare like
a relatively bright - it's probably relatively icy rich region from the
north pole of the leading hemisphere up in 5 and then another relatively
bright area down here in 4 more in the boundary region.

And on Slide 70, we're ratioing Region 5 \-- sorry \-- Region 4, two
region 5 and we see the signature that I showed you before of water-ice.
And this tells us that that bright area in Region 4 is probably richer
in water-ice than the right area in Region 5 in that north polar
terrain.

But it also tells us because at the shorter wavelengths, we can see kind
of a reddish slope, very slight but it isn't as flat as we would expect
it to be as the - the difference were only due to the amount of
water-ice present. But if not boundary area, there might be some other
stuff mixed in that is slightly reddish in color.

Okay. And then, next slide is the same one I already showed you but now,
we're going to compare some of the low albedo regions \-- the visibly
albedo regions.

And I think we're going to compare 1 and 2 but this is - 1 is important
because it's at the apex of the leading hemisphere. And so, if there is
stuff coming in from an oxygenic source, this is where we'd expect the
fluff to be highest and maybe - well, anyway, I'll leave it at that.

And so we're looking for color variations if they exist between 1 and 2
and that will tell us again about any mixing of material maybe endogenic
material that has come up from below and been (gardened) and also the
amount of volatiles that are present.

So on Page 72, we've ratioed the Region 1, the apex Region 2,Rregion 2,
this is the FUV ratio and you can see that it's not flat and this tells
us that region 1 has - well, that they're probably compositionally
different.

And the way that we're interpreting this right now is that one is richer
in some sort of absorbing material than 2, and it looks like it could
have a very broad absorption feature in the (FUV) region.

In Slide 73, this is a reminder - okay, we don't have very many lab
spectra of candidate species in this wavelength range because it's kind
of difficult to work in the lab and not many people have made
measurements but we can use what we have.

And compare on Page 74, spectrum of an ice stolen to our absorption
feature that we think we're measuring and we see that we don't really
get a very good fit- especially at the longer at the longer wavelength.

But then on Slide 75, we compare with carbon and it's a little bit
better. It's pretty hard to say with such a broad band and with not very
distinctive absorption features in the (FUV) that, you know, this is a
sure fit or anything, but it's consistent with a story of carbonatious
material maybe coming in, and maybe being a little bit more concentrated
at that apex region.

Slide 76 shows some UVIS results from the earlier flyby where we - we're
able to get latitudinal information within that apex region of the dark
leading hemisphere.

And looked at the water-ice band and showed that it becomes stronger as
you go away from the equator and that it is present weekly though at the
lowest latitudes.

So we think we're sensing water-ice mixing with the dark material as
shown by that lead spectrum which does show a weak water-ice feature.
But these results here are consistent with the thermal segregation model
because we do expect there to be more water-ice as you get colder
towards the higher latitudes.

So slide 77 is sort of summarizing these things of just saying here,
then maybe I won't go into them too much. But 78 at low latitudes and
this is one thing that I guess that I actually didn't go into too much
but two of the regions, Region 2 and Region 3 that we pulled out here so
far do have varying amounts of water-ice evidently present.

And this could actually even in Region 1, there could be fresh bright
craters with exposed water-ice that we just are not that are below the
resolution of the images there and so we don't know that they are
present but that could be the first of the water-ice just have to be
volatile next in with the dark material but both are options here.

If it is volatile next in with the dark materials and that would suggest
that it's a recent process that's happening here although that may not
be entirely consistent with the time scales that we're talking about
with the thermal segregation and the temperatures.

So just to kind of conclude on the UVIS results is that we still have a
lot to do with the data because we got such a big and great data sets so
we're still working on it. But we're using the data sets to map out
water-ice and to look into the thermal segregation.

And also to look into the non-water-ice materials and how the color
varies across this dark hemisphere and to look at compositional
variations and see if that tells us about the exogenic material compared
to the endogenic material. But generally, the data are consistent with
John Spencer's thermal segregation model. And that's it for UVIS.

Trina Ray: Okay, great. Do we have any questions?

(Amanda) Right now?

Trina Ray: Okay, we'll save all the questions for the end then. (Steve)
are you online?

(Steve): Can you hear me?

Trina Ray: We can.

(Steve): All right.

Trina Ray: Go right ahead.

(Steve): Okay, can I have a - actually, this is Slide Number 81. We're
now going to change gears a lot because radar is sensitive to different
physical phenomenon and optical techniques.

And in many cases there are factors involved that we really don't have
to worry about with optical remote sensing. And perhaps all of these
stems from the fact that the radar wavelength is macroscopic.

The Cassini radar wavelength is 2.2 centimeters, a little bit less than
an inch. We also have some ground-based radar data that turn out to be
very important from Aresibo working at a longer wavelength about 13
centimeters.

Now on this first slide, I\'m plotting an albedo, a reflectivity and
I\'m showing some of the results that we have from radar, they\'re the
small symbols. And I\'m also showing the optical geometric albedo near
the large circles and everything is plotted as a function of distance
from Saturn. And you can see that things get brighter as we get close to
the Saturn regardless of whether we are talking about radar or optical
technique.

With the little symbols you can see there's a fair amount of spread. And
only a fraction of the available data are plotted here because we're in
the midst of reducing it; we're in the midst of refining our
calibration. So virtually everything I show you today is a little bit of
our work in progress.

However, you can see that there's this wonderful correlation between the
optical and the radar albedos. Now you start out on the left with minus
and then you go up a little bit with Enceladus and down a little bit for
Tethys. Then you drop down a little bit for the Dione and Rhea, go on to
Hyperion finally to Iapetus and Phoebe.

So there's pattern here and because the optical albedo is sensitive to
dark - optically dark material, the optically dark material has to play
some role in the radar albedo, but it is not the only role - not
necessarily the only role and probably not the only role.

Now let me talk a little bit about what is going on with the radar
scattering from these icy surfaces. This is now on Slide 82.

Ice is not reflective at radar wavelength. It has a low dielectric
constant. If all the satellites of Saturn were just icy spheres,
homogenous icy spheres, then the radar albedos on the previous slide
will all be down by the horizontal axis. So something else is going on.

And what\'s going on is multiple scattering. It turns out that ice is
possibly the most transparent geologically important material that
exists in the solar system. Radio waves just don't get absorbed when
they travel through pure water-ice.

What this means is that if you have a surface that has heterogeneity of
any source whether you have particles or you have density variations or
you have gradients as long as you have some kind of heterogeneity
anywhere near the scale of the wavelengths, then the incident wave will
come in and it will be refracted and it will be reflected and it will
bounce around but it will not be absorbed.

And sooner or later there's a good probability that it's going to exit
in the direction from once it came. And this is why clean icy surfaces
in the solar system and Europa, Ganymede and Callisto and throughout the
Saturn system are much brighter than they'd be if we were just looking
at a homogenous ice surface.

We're seeing structure as well as the effect of composition namely the
purity of the ice. So in general, if we have very pure ice we see a very
bright radar response and as the ice gets dirtier from whatever cause,
the radar albedo drops. That's what\'s going on.

And in the nutshell, this is a context that we use to try to understand
the radar echoes from icy satellites in Jupiter and Saturn systems as
well as icy surfaces at the poles of Mercury and Mars and certain other
places as well.

So let's go on to Slide 83 which has a table which conveys the severity
of the reduction and transparency when you put anything into water-ice.
You can put terrestrial rocks. You can put nonmetallic meteorites. You
can have lunar soil. You can put in ammonia. You can have organics. You
can have trace amounts of nano-phased iron which is a possibility.
Almost anything that's going to drop the absorption lengths, not just a
little but a lot by orders of magnitude. So we are hypersensitive at
radar wavelength to ice purity.

Let's go to the next slide which show - this should be slide number 84
right now and these are the Iapetus results that we have condensed into
a little table.

We know two things. The first is at 2 centimeters of the Cassini
wavelength, there's a tremendous dichotomy more than a factor of two
between the radar albedo of the optically dark leading side material and
optically bright trailing side material. So we see this dichotomy that
just jumps right out of dust. And I'll give you some details in the
moment. So that's the first row of the table.

But then we just go up the factor of about 6 or so in wavelength and all
of the interesting properties of the Iapetus vanish. We no longer see
the dichotomy in a pronounced fashion. There may be a hint of it, but
the albedo's drop on all over the place and if someone showed me the
echoes at 13 centimeters from the Iapetus and said, "Well, what object
is it? I'd say, well this is a perfectly ordinary main-belt asteroid in
every single respect."

So what\'s going on? What\'s going is the 13-centimeter wavelength is
getting deeper. A factor of five or six deeper than the two-centimeter
wavelength. So how we do understand this?

So let's go to Slide Number 85. We can understand these results if there
is something in the uppermost part of Iapetus's surface that is
degrading transparency of ice.

Now my first guess was ammonia back when we first saw this phenomena on
a couple of years ago because we know that ammonia has to exist in the
southern system of certainly in concentration much higher than we see in
the Jupiter system and that we know that ammonia has a tremendous effect
in reducing the transparency of ice, however it isn't necessarily
what\'s going on with the possibility of virtually anything from the
previous table, any kind of sorted organic or metal, almost any kind of
contaminant including whatever the dark material on the Iapetus is made
out of.

But there\'s a lot less of it whatever it is in the uppermost part of
the surface than when you get down deeper and when I say down deeper, I
have to hedge my best because this is a complicated scattering process.
By deeper I could mean a few decimeters or it could be a few meters, but
I think it's in that realm.

So, to the ice of radar, the upper most part of surface of Iapetus is
clean every where, however the leading side is dirtier than the trailing
side at least down to depths of a few decimeters.

You have to be talking at least in a few decimeters or a scale of a few
decimeters when you have a wavelength of a couple of centimeters because
you've got to have enough thickness for the multiple scattering to
really happen and give us the echo that we see.

But once you get down deeper, perhaps a few meters, something else is
going on and we don't know what it is. My best guess I think still is
that there\'s ammonia underneath the optic we\'ve seen surfaces of
Saturnian satellite because we see this kind of phenomenon to some
degree on other Saturn satellites. If there is ammonia underneath the
surface, but not right at the surface, then you're going to quench the
radar signal and indeed the (ICR) objectives going to look like a
typical main-belt asteroid so that could be what\'s going on.

You can have a distance dependents of the removal of ammonia from the
surface because you have micro meteoroid crater ring impacts that get
more severe as you go inward towards Saturn and you also have
magnetosphere effects like spattering at least once you get inside
around Titan.

So, we're seeing under the surface, not the surface per se. We're seeing
things that macroscopic scale and there\'s various phenomena that can be
going on to explain what we're seeing.

And we go to the next slide. Now, I want to move to the issue of spatial
resolution up until Iapetus 49 virtually all radar observations of icy
bodies in the solar system did not have two-dimensional resolution.

Instead of having resolution of the radar echo in range and Doppler, we
had - just in Doppler so we had spent the last three decades looking at
echo spectra which are like one-dimensional images scans of radar
brightness taken to a slit held parallel to the apparent spin vector as
you see on the left of the Slide Number 86. And that's all we've had \--
echo (power) spectrum and then we add up all the echo and the spectrum
and we convert that to a radar albedo.

With Cassini - and let's go to the next slide, Number 87. Many of our
observations of the satellites have used a beam large - as large as or
larger than the disk of the object, but in a few cases including the
situation with Iapetus, we\'ve used a beam that is smaller than the disk
1/2 or 1/3 or even smaller than the diameter of the disk and this is how
we've discerned the heterogeneity of the radar albedo on the object.

And let's go to Slide 88. Iapetus 49, we finally got close enough to an
icy satellite where we could do the same of kind of imaging that's used
for the (unintelligible) of Titan on using the Cassini radar.

Now, the geometry was a little bit different so we didn't get quite
resolution that we get on a nice Titans or flyby, but we do have
two-dimensional resolution of much of the dark side of Iapetus. Our
pixels are typically rectangular with one dimension as fine as two
kilometers across and the other several times that. So the Doppler
resolution is typically 6 kilometers and the range resolution goes from
about 2 to 12 as you can see from the diagram on the left of Slide
Number 88.

During the flyby we did a kind of roster scan up and down doing some
turns, going across the dark side building up an image of the object.
And we'll go to Slide 89 which is schematic that shows on the left and
ISS and optical map of Iapetus, now, this is from December of 2005. The
vertical line shows the limit of the high risk ISS imaging of Iapetus
during flyby Number 49 and on the right is a preliminary version of the
radar SAR image.

With radar in order to produce a map you have to have a very good table
of distances and motions for the object that you're looking at in other
words you need ephemeris for the object and the demands on the ephemeris
are much greater for radar especially for radar imaging than they are
for other techniques.

So we're using the information from the Iapetus 49 flyby to produce a
better ephemeris. The mission is almost finished with and then we'll be
able to properly focus our data and we really what kind of information
we have in the image.

Similarly, we do not have a good calibration for this image yet, but it
is coming and we should have all that information within a month.

And nonetheless, you can look back and forth, left and right from this
Slide Number 89 and you can see that there\'s a high degree of
correlation between the structure into the eyes radar and to the optical
remote sensor.

So, virtually anything that you can find on one side you can find on the
other although the appearance is very different and the reason for that
is that with radar we're a little bit more sensitive to large scale
structure and also the radar and scattering law might be different from
the optical scattering law.

But also, we are seeing underneath surface. The radar is seeing a
surface which here is probably as deep as a meter and radar and is
sensitive to phenomena that involved different civics from what the
optical sensors are sensitive to.

In particular the cleanliness of the ice that we have structure in
composition and we have compositional effects that might be a little bit
strange. Hence, if you look at the large basin that's prominent on the
left, you see that basin on the right and the SAR image, but you see a
lot of brightness, you know, where does this brightness come from?

It could come about because the reflectivity is intrinsically brighter
in other words the ice could be underneath the surface, it could be
cleaner than the surroundings or it could come about because the
geometry just conspires more in this space than other places to produce
smokes that are facing the radar and hence, giving a brighter
reflections or you could have a different distribution of ejector of
small wavelength size icy rocks in this basin region that you have
elsewhere in the dark terrain, it could be any weighted bunch of
contributions from all those possibilities.

This is an uncalibrated image on the right, so it\'s difficult at this
point to try to go further in identifying exactly the correlation
between radar bright and dark versus optical bright and dark. That's
obviously one of the primary things we want to do, but we have to wait
for a better calibration.

What you're looking at on the right is the first radar image of an icy
object in the solar system for which we also have good high resolution
optical images, and we've been waiting 30 years to have this kind of a
data set. Certainly, what is established is right off the bat even
before the focusing and calibration is that we see a great deal of the
structure on the surprise to the eyes of radar, the fact that we're
going to down a meter isn't going to affect our ability to see traders
that are many kilometers or tens of kilometer in size.

And so we have a new found confidence \-- an observational confidence in
the ability of synthetic aperture radar to see the surface of an icy
object even one that's covered with an atmosphere like Titan. So, we now
have even more confidence than we had before in the validity of our
interpretation of the images that we've got into the eyes of the Cassini
radar for Titan. Of course, we don't see anywhere new the number of
craters on Titan that we see on Iapetus.

Let me go to one more slide and that's the final slide which shows
scatterometry \-- radar scatterometry which is low spatial resolutions,
but it is very easy to calibrate and the calibration is almost
instantaneous.

And what we see here, the red is bright and the blue is dark, we see
good correlation between radar bright dark and optical bright dark
except for there\'s an incursion of the radar bright terrain, right on
top of the prominent basin that we see optically.

There is some work to be done to make sure that this is true, however if
it is true, it does require an explanation that will undoubtedly be some
combination of structural ideas and compositional ideas.

So, this is a status report what the radar data do give us is a kind of
a leverage \-- a kind of insight into what\'s going on underneath the
surface and just coincidentally, the radar wavelength of the Cassini
instrument is ideal for trying to understand what\'s going with that
redistribution of ice on this object with vertical profiles of ice
versus dark material. And because we're seeing down into the surface,
we're also seeing at least in some sense into the past and so we're
hoping that we're going to be able to constrain the situation with
Iapetus now and also how it got that way.

I think I would stop there.

Woman: Okay, let's go ahead and open it up to question.

And remember to press star-6 if you're muted.

Actually, I guess I do have a question since I've got all of you on line
here. You know, before we got to Saturn, it's sort of the bright dark
dichotomy was the big question and then there\'s a ridge and whether -
all the way around what created it is the big question. What do you guys
think now as sort of the big open question for Iapetus?

Man: Well, I think we still don't know where the dark material come
from.

Woman: Right. (What that exogenic source is).

Man: Yeah, we have possible ideas and on the some of segregation model,
it could be that most of the (unintelligible) we see on the site is
actually from inside the surface there by Iapetus and it simply
concentrated (unintelligible) there by thermal segregation that's
triggered by material falling from outside, but we do not show what that
trigger material is, that we - coming from (CBO) the other outer (moon),
often interplanetary space and that's - so that's still very much up in
the air. And we still don't understand the equatorial ridge. To me it\'s
still a big mystery and I\'m hoping to sort of analysis that the Cassini
data will have to make more sense of Iapetus, it's very deserving.

(Greg): Sir, this is (Greg Sirmack). Those in the article published
earlier regarding the ridge and the fact that it was a molten at one
time and seemed to freeze early on into its current form. Can you
elaborate on that?

Man: I could have it go with that. Yeah, that's not so much about the
equatorial ridge. It's about the equatorial bulge which is a different
thing. As in addition to this quite narrow ridge that runs around the
equator of Iapetus, the whole shape of Iapetus is out of round. It has -
it\'s quite (unintelligible) of the equator compared to its polar
dimension. And it's the shape it would be if it was spinning with
instead of a 79-day period with I think about the 17-hour period.

So, it\'s - with one spinning very fast and it was quite soft inside, so
it's bulged out to (unintelligible) with that (bead), but then it froze
in that position of - in that state and then, slowed down and so, it has
this puzzle bulge as we call it. It's large out of roundness which is
not consistent with its current rotation rate.

And so that requires a very specific timing of the events during the
cooling of it, that it had to have been soften enough to get into that
shape, in the first place and then, it had to be - and hard enough to
keep that shape as it (run) down and also have to be soft enough to spin
down because it was really (unintelligible) very early on. It would not
have (spin) down and it will still be spinning in a non-synchronous way.

(Greg): What actually causes the slow down of rotation?

Man: Caused by the types of Saturn acting on Iapetus and it\'s the same
thing - the types of (Earth) acting on our moon caused the moon
towards - show the same face towards - yes, it's the same thing on
Iapetus with Saturn.

But those types are really very weak on Iapetus because it's so far from
Saturn, so Saturn side effects of, you know, have a very small effect
and so, you need very specific circumstances for those actually to stop
it rotating and make it - put it in a synchronous rotation as it is
today.

(Greg): There were also some comments earlier on the slide about iron
oxide being present that might be a possible source for the darker
materials. Do you have any idea where that might originate from?

Maybe (Roger) can take that.

(Roger Clark): Well, I\'m trying to think - I don't recall anybody
saying iron oxides per se, we understood not...

Man: Or maybe (Steve Auster) said something about nano-phase iron.

(Roger Clark): Oh, nano-phase iron is a very different and in fact the
very linear spectrum of the dark material of Iapetus looks very similar
to nano-phase iron, so yes there could very well be nano-phase iron
there.

(Greg): Okay. Thank you.

Woman: Do we have any other questions?

Woman: Actually, you know, we had gotten an email from someone called
(Matt Miller). I don't know if he's on. But maybe I'll read the question
and anybody who wants to answer can chime in that (Matt) can his answer
when he listens to the audio. No, (Matt Mill), sorry, who is an amateur
astronomer and his question is, "Could the strange appearance of Iapetus
be due to a gamma ray (burst) and then, subsequent capture of the moon
by Saturn's gravity long after the event?

Man: I think that's speculation at this point. I suppose the idea is
that the intense radiation from a gamma ray burst would darken the ice
on the one side and or I suppose you can imagine something like that,
but it would be not clear why Iapetus would be the only object to be
dark on one side because the gamma ray burst would affect with
everything in the solar system.

And then also why it was so being captured in such an orientation that
dark part was exactly facing forward in its orbit. So, I think that's a
bit a long shot.

Woman: So, are there any upcoming Iapetus observations that you guys are
looking forward to?

Woman: You know, what Tillman is doing a lot of is observations of the
outer dark moon that are even exterior to (PB) I think sometimes just to
see if the color is going to match at all from what ISS images tell us.

Man: We don't have anymore close flyby Iapetus for the rest of the
mission. And we don't even have any as close of the New Year 2005 flyby
and so there'll be other opportunities to look at it, but there will be
very distant and the images will not be very (sharp), but they may still
allow us to look in particular lighting condition or particular angles
that we have been seeing it, so there will still be valuable stuff to
come, but this was the big one and there'll be nothing that good in the
future unless in some later part of the mission those decisions may go
back to Iapetus.

The extended mission which extends through from the middle of 2008 until
the middle 2010 does not include any Iapetus flybys which was disappoint
them, but there wasn't really any way to get that in, so we're all going
back in that period, but it\'s conceivable probably not very likely, but
conceivable that after the middle of 2010 there might be an opportunity
to go back.

Trina Ray: Okay, does anybody have any final questions?

Okay, well, with that we'll say thank you to our scientist. We really
appreciate you guys taking the time to come and share with us your
exciting Iapetus results, so everyone was really looking forward to
Iapetus flyby all these years, so it's been a pretty exciting month for
everybody.

And (Amanda), do you have an advertisement for the next time telecon?

(Amanda): Let's see, what is the date, last Tuesday of November...

Trina Ray: Right, the 27th.

(Amanda): ...and the topic is going to be "Titan's Lake."

Trina Ray: Titan's Lake, wow great.

And then, also just reminded everybody on line that we typically take
the month of December off, so there will be no telecon in December.

And with that we'll close it out and thanks again to everyone.

Man: Thank you.

Woman: Bye.

Man: Bye.

END