**FTS-NASA-VOICE**

**Moderator: Trina Ray**

**October 31, 2006**

**1:00 pm**

Coordinator: Thank you for standing by. At this time the call is being
recorded. If anyone has any objections you may disconnect at this time
and you may begin.

Trina Ray: Thank you very much. Welcome, everyone, to the CHARM telecon
for October, 2006. Today's topic is compositional mapping of Saturn
satellites with Cassini VIMS and we are joined today by Dr. Roger Clark.
He's a team member of the Visual and Infrared Mapping Spectrometer and,
with that, I will turn it over to Dr. Clark

Dr. Roger Clark: Hello, let's see, as the title say, I'm going to talk
about Saturn satellites and, in particular, the composition of the
satellites and, in general, the satellites are very Icy objects. I'm not
going to discuss Titan today. I'm going to talk about the Icy
satellites, just because there's too much to fit in one - one talk.
Titan could be several talks in itself.

So the Icy satellites, while they're composed mostly of ice, there are
contaminants on them and that's been the focus of our study. We've known
for decades that the satellites are icy from Earth-based telescopes and
spectroscopy of the satellites.

So, going to slide two, let's see, this was the original title of my
talk but a lot of the content of this talk will be in a paper that will
be submitted to ICARUS pretty shortly so most of the stuff here is
either public domain or going to be in this paper.

So let's go to slide three and this just shows some of the complexity
that we're dealing with and, while you've seen many complex pictures and
I'm sure many of you have seen this image before, it illustrates some of
the problems we have in trying to do spectroscopy. It's easy to take
pictures but when you have things shining light on other things and
casting shadows and all kinds of stuff, in spectroscopy you see those
signatures and you have to be sure that you're not contaminating a
spectrum with something else.

For example, Mimas is showing in this one, toward the upper , and Saturn
behind it would be shining light onto Mimas and so trying to get a
spectrum of Mimas may be pretty difficult without the contaminated
Saturn shine.

So then, and some things may be obvious in the visible but not in
other - in the infrared - so trying to figure out the scattered light
has been a far more complex issue than we've thought we would have to
deal with. And to illustrate this a little better, this next, we're on
slide three, and it's kind of obscure geometry here, but if we zoom out
a little to another view, it gives a better view of the Saturn system
here with the rings edge on and the light from the sun is from the lower
light, shining up through the rings, casting a shadow onto the disc of
Saturn.

That's slide four, and if we go to slide five we get a similar view from
VIMS and here we see that not only does Saturn reflect solar light and
at long wavelengths, in this case in red, is the five micron thermal
emission. So if we're studying, for example, a spectrum of a satellite,
there could be thermal emission scattered light onto the satellites and
trying to interpret that would add more complications. And since the
satellites are pretty close to Saturn, this is a continual problem that
we're having to deal with. I think many have probably seen this picture
because it's been press released. But it's a pretty cool effect of all
the issues that we have to deal with in general.

For - as an analogy for scattered light, if you're studying the moon,
when the moon is a crescent you often see earth shine and that earth
shine, if you were trying to take a spectra of the moon even on the lit
portion of the moon, there's earth shine on that part, too, and with
spectroscopy you would see spectral features due to earth and - in your
spectra of the moon and you might say, "Oh, there's oxygen on the moon",
which would be incorrect.

We've had a number of times when we thought we might be detecting some
organic compounds on both Saturn's rings and the Saturn satellites and
it's turned out to be scattered light. We have definitely detected some
organic compounds on some of the satellites but we've had quite a few
false alarms where we had to back off. So we're tracking the scattered
light issue pretty carefully.

Let's move on to slide six. I prepared this talk before seeing all the
term talks and Trina and I did a whole bunch of downloads of the term
talks in the last couple of days and saw that others, I think (Kevin)
may have shown this slide. Anyway, VIMS is - it's an imaging system that
has 352 wavelengths compared to the, like a digital camera only has
three. And the field of view of VIMS is nominally 1/2 by 1/2 milliradian
and that equals 1.7 arc minutes. And then it has high resolution modes
that double the IR in one dimension and triples the vis in both
dimensions.

And so to a first approximation, what VIMS sees would be like if you
were standing on the space craft looking out you would see about the
detail that VIMS sees. When you see these pictures from the imaging
camera, especially the narrow angle camera, that's like looking through
a small telescope from the space craft; if you were standing on the
space craft with a small telescope. But VIMS is more like standing there
and just looking out.

Let's see, I'll go on unless there are questions that come up. The
wavelength range, .35 to 5.2 microns, allows us in the infrared, to see
the absorption bands due to stretching of molecules and, in particular,
water and CH bearing compounds; the CH stretch, the OH stretch, the NH
stretch and ammonia compounds all occur in these wavelength regions and
spectroscopy is quite sensitive to these compounds. We can detect them
at pretty low abundances.

Let's go to slide seven. So I'm going to discuss the icy satellites and
this is an overview of the Saturn system and I'll start from the
outermost major satellite, Phoebe and work my way in, skipping Titan and
I'll really not talk about the very small satellites. VIMS is getting
spectra of the small satellites and, for the most part, they're pretty
pure ice.

The one theme that will come out of this is that, while there are
contaminants like you see the dark stuff on Iapetus and Phoebe is pretty
dark, as we move in toward the rings, the ice gets - on the surfaces,
gets purer and purer. And we have the purest ice in Saturn's rings,
which it's an interesting conclusion and may have some global
implications for the Saturn system.

So, let's go to slide eight, which is the ISS views of Phoebe. Phoebe is
a very dark object. It's got some, in the finest details of the imaging
system. There are layers that show in the crater walls so there are
compositional variations that are implied but in the next slide, slide
nine, we see how rich the spectra really are. This was published in
Nature in May, 2005 and it's just a global average and the spectrum is
pretty complex and we don't understand everything yet. And the Phoebe
fly-by data are noisier than what we're getting on more recent data from
all the satellites.

And I want to point out just a few of the spectral features. A few of
them, like F2, 3 and 4 have turned out to be calibration errors and are
not real. And in our newer data this - that spectra region is smooth. F6
and 9 are water bands and there's two kinds of water in there; there's
both water ice and bound water. That's H20 molecules attached to other
compounds on the surface. F11 is a very interesting feature that's
called the 2.42 band and you'll see me refer to that quite a lot. It may
be related to cyanide compounds and, initially, after the Phoebe fly-by,
we identified it pretty solidly as matching cyanide compounds and, to
this day, cyanide compounds are the only compounds that match but there
are other absorptions that cyanide compounds should have that we don't
always see so that may not be a cyanide compound. It may be some other
compound that we just have never measured on the Earth so far.

Man: Excuse me, I have a question.

Dr. Roger Clark: Yep?

Man: Could you briefly describe the concept of absorption and how it
shows up in this graph in terms of magnitude?

Dr. Roger Clark: Well, okay. Basically, any wiggle, any dip from some
trend, like that F11, there's a peak just to the left of F11; that's the
maximum in the whole spectrum and then the spectrum is coming down and
then it suddenly drops giving where F11 is pointing. That is a little
absorption feature and, whether something is significant or not in
spectroscopy, a little feature could be quite important. So a lot of
these little wiggles here, depending on what they are, may or may not be
significant and could be major discoveries.

For example, let's see, let's go over to F18. There's a little tiny dip
there in the trend and there's a big, broad thing going from about 3.8
to 5 microns called F21 and that's a big, broad thing. That's a big,
broad absorption band mostly due to water. But F18 is very interesting
because it's due to a nitrile. A nitrile is CH compound with a C N
molecule attached to it, or a CH bond, a bond CN attached to it. So...

Trina Ray Dr. Roger Clark

Dr. Roger Clark: Yes.

Trina Ray Could you maybe give, like, a one minute summary of what's
physically happening with the atom that creates an absorption line?

Dr. Roger Clark: Yeah, it's very simple. It's, think of two masses and a
spring. So when, if you have two masses and a spring and, depending on
the - how much each mass weighs and the strength of the spring, if you
hit it it'll vibrate. And it's the same with molecules. You hit it with
a photon and if the photon matches the resonant energy of that spring
plus mass, the spring being the chemical bond and the masses being the
atoms, then the atoms will vibrate at that frequency. So, like F18,
what's happening is there's a CN molecule and when a photon hits it at
that wavelength, it is a resonance that sets up the vibration. And in
spectroscopy, you need a dipole moment for the electric field of the
photon to interact with the molecular bond, or chemical bond.

So things like N2, there's no dipole moment because they're both the
same and an N and you don't tend to get, well, you don't get any
absorption bends due to nitrogen. For example, through the Earth's
atmosphere we can look out through most wavelengths because there's no
nitrogen absorptions. We do, or can't look out through the atmosphere
where the oxygen and hydrogen vibrate and that's quite a few lines in
the infrared. Basically, where there's F6, F9 and F12, those are water
bands and in the Earth's atmosphere, like the F12 region is completely
opaque to viewing.

So spectroscopy is very sensitive to these molecular bonds and light
elements for the near infrared. If you want to do heavier elements like
silicates, then it's better to go out into the longer wavelengths into
the mid infrared. So every wavelength has its strengths.

Does that clear that up okay?

Trina Ray Yeah, that was great, thanks.

Dr. Roger Clark: Okay. So, anyway, the Phoebe spectrum turns out to be
quite rich in features. We don't understand everything yet and, in fact,
the F8, F9 and F10, we're going to see that complex over and over again
and we'll see the F11 and the other one that's important here is F17 is
CO2 and we know from the position of that it's not free CO2, it's not
CO2 frost, it's CO2 trapped in other minerals. The F6, F9 and F12 are
the water bands and ammonia also has absorptions there so sometimes
there could be significant amounts of ammonia contributing to those
absorptions, also. But ammonia, if there's too much of it, it has other
absorptions and we basically have not detected ammonia.

Woman: Do you know how to mute a cell phone?

Trina Ray: Star 6.

Dr. Roger Clark: Star 6 works there, too?

Trina Ray: Yeah.

Dr. Roger Clark: So while there's a fair amount of ammonia here, we
can't directly detect it unless it becomes fairly abundant, like 10% or
more. The other interesting feature, which you'll see repeated, is F13
is a peak instead of an absorption. And that is due to where the OH
molecule has a resonant frequency called the fundamental. Some of these
are combinations and overtones of different modes. If you think of music
and you think of overtones with music, this is - the F13 is the
fundamental OH stretch vibrations for OH and that is where it's such an
intense absorber it actually reflects light, like a metallic mirror.
It's just a strange property of - all materials have this; this kind of
things.

Okay, let's go to the next slide because we could talk about this
forever and really get bored. So using all those features, just like in
a digital camera, you have three channels. VIMS has 352 channels. So
every pixel, we have a complete spectrum. And while our spatial
resolution isn't as high as the imaging system, we still have pretty
decent resolution when we get close. And so these are maps produced for
Phoebe. Every one is -180 to +180 longitude and - 90 to +90 latitude. We
did not observe the northern sections so all the maps are blank there.
So we've got the southern pole up through a little beyond the equator
into the north a little bit. So these just show examples of the kind of
maps we can make and, like, A is just intensity at one micron wavelength
and then B is the strength of the two micron ice feature. So this is a
map of ice abundance and it's a combination of ice abundance and ice
grain size. So spectroscopy will change the strength of absorption
bands, depending on both their - the depth and the grain size of the
material. So and using multiple absorption bands, we can sort out which
is which so we can map both abundance and grain size, which is pretty
cool.

Then what's some of the others? The CO2 absorption down there in G has -
there's two maps. There's the general global view and then the close-up
picture just below it that shows the small craters. And one thing that
was curious in the CO2 absorption map is there's a dark line, meaning
less CO2 that is some geologic structure that extends over the length of
the image. And that we don't understand but, in general, a lot of the
moons have a lot of long range fractures in them so this must be one of
those fractures being illustrated there.

Phoebe does have some organics as shown in Panel F there and they seem
to be concentrated in one area. Let's see, the ice in general is, as you
might expect, is more abundant at the South Pole than it is at the
equator. But there is ice all over the place. And where there's not ice,
most of Phoebe's surface has to be, oh, 80% or 90% ice everywhere
because we see the ice absorption everywhere, even though it's very dark
and this will be a repeated theme.

Think of charcoal; if you're, say, barbecuing and you get some charcoal
on your finger and you smear your shirt. That smear shows up very
easily, even though you're not putting much abundance of charcoal onto
your shirt. Any dark material at a given wavelength will dominate
because when a photon hits it, it gets absorbed whereas, like, in a
white shirt the photons can go in, hit the shirt and bounce around on
different fibers and then be scattered away. But the dark materials
dominate so it's a very non-linear effect. So even though you have a
very dark surface, it can still be very abundant with a bright material
like water ice, although water ice isn't bright at all wavelengths. It's
only bright to us in the visible way we see it.

Okay, let's go on to slide 12. Let's see, okay; pushed the wrong button
here on my computer. We were - slide 11, excuse me. Okay, so using some
of the compounds from slide ten, you can combine those into different
colored, you know, like assign water to green or blue, in this case,
like Panel I shows blue as the water ice strength, green is that little
2.42 micron band, the strength of it and red is, if you want to jump
back to the slide nine, it's feature F1, a big, broad feature that
appears to be due to ferrous bearing minerals.

Go back to slide 11. These are just some examples of some of the things
you can do and, from there, these might show you geologic units that you
can then help interpret the geologic history of the object and we have
more papers coming out on things like this. Now we'll have one on
Enceladus coming out shortly that will have more of this kind of stuff
and, in that case, mapping the ice grain sizes.

Let's go on to slide 12. So these are some of the conclusions for
mapping Phoebe. Again, at the top we're dominated by water ice. We also
have bound water; those are water molecules that are bound - chemically
bound to other minerals. We have the trapped CO2. We have the broad one
micron feature, which appears like FE2+, although we've actually come up
with a novel new explanation and we're trying to verify this; it's
certainly a possibility and it will be hard to prove if it's correct or
not but that is, if you have small grains of dark material embedded in
ice and those grains are smaller than visible wavelengths, toward the UV
it'll cause what's called Rayleigh scattering and cause a blue increase,
much like we see our sky is blue due to rayleigh scattering off of
molecules in the earth's atmosphere. So this effect, we've observed it
in the lab now and it appears similar to what we're seeing on Phoebe. So
instead of this broad absorption being due to and FE2+, it might be a
flat reflectance material like carbon that doesn't actually increase in
the blue but the blue is caused by scattering. And we're trying to
verify that. I'm not sure if we'll be able to. We'll probably just have
to put it down as another explanation. Science doesn't always give all
possible explanations, uniquely.

So we also see a 2.2 micron feature, which is most likely due to
phylosilicates; that's clays. Phylosilicates are commonly seen in
meteorites so this isn't an unusual finding. It just extends further out
into the solar system where we're finding these. Then this 2.42 micron
feature, which we're still wondering if it's cyanide compounds. At
present, it's our only explanation but we're really confused by it and
we can't reproduce it exactly in the lab so we're trying hard to do
that.

We see organic compounds, due to this 3.3 micron set of features, again
that the features don't exactly match things that we have in the lab but
organic compounds are the only things that match in this area. We have a
3.6 micron feature, which is - I think probably is also an organic
compound but we don't have a match for it, either.

We have these broad absorptions, which we don't have exact matches for.
They're probably water related, could be NH ammonia related, just
confusing. Can we put on the slide, oh there, down at the bottom; the
nitrile, the 4.51 micron feature, that's pretty solid because it's a
very sharp, narrow line and it's right on the position of known nitriles
so it's probably a very good identification.

So let's move on to the next object in the Saturn system and that's
Iapetus. One of the big questions that Cassini was hoping to answer is
the - one side of Iapetus is dark and one side is bright and we will
have a very close fly-by coming up in September 2007, where we should
get the definitive data. But the spectroscopy of Iapetus is kind of
curious because, from the earth, Phoebe has this blue upturn so it - the
blue shape of the spectrum does not match that of Iapetus. Iapetus's
spectrum toward the UV doesn't go up like Phoebe does. So people have
argued, "Well, it's a different material."

Well, let's go to - is it the next slide? Yeah, okay. So, more - slide
14, what is the source of this albedo dichotomy? The question is is it
stuff coming from Phoebe? Is it stuff coming from Titan or Hyperion? Or
it stuff that was from Iapetus itself. So there's a lot of questions on
the origin of this material and another option is all of this stuff has
come in from outside the Saturn system.

Let's go to slide 15. One - some of the evidence for coming from
external to Iapetus is the ISS; these are the camera views from the -
our first, sort of, close fly-by and we see these, what look like wind
streaks of this dark material so like it's being blown onto the surface.
So it does appear to be coming externally. And there's probably several
people who will argue different positions, even based on that but I'm
not going to get into that.

I'm going to go - let's go to slide 16 and look just at the spectrum and
see what that says. Well, right off the bat we see that we have the 2.42
micron feature and we have the trapped CO2 feature and then we have
what's marked there around 2 microns three features. We also see those
same three features on Phoebe and then note that, as you go toward the
short wavelengths, the spectrum of Iapetus is very smooth and continues
down. I didn't plot the UV but it continues down, all the way down to
the shortest wavelengths that VIMS measures. And the spectrum is very
smooth compared to Phoebe in the 1 micron region. That's reflecting the
new calibration that we have now and the Phoebe spectrum looks smooth
there, too, now. Trying to do calibration is very difficult.

So at 3 microns we have the huge absorption band; same kind of thing
that we see on Phoebe. Then over at 4.8 microns, 4.9 microns we have
this change in the spectrum that is labeled the xCN. This actually is
some of the stronger evidence that that plus the 2.42 feature are due to
CN; that this structure out at 4.8 microns is very similar in structure
to spectra seen in interstellar clouds, where the interstellar
astronomers are calling it xCN. And, unfortunately, we don't have
whatever that material is; at least here on earth, measured in labs to
reproduce that exactly. So that's why I keep putting question marks on
these things. I would like to see a good, solid lab spectrum that
matches it exactly because the problem with spectroscopy is you can be
close and not quite and if it's not quite it may be something completely
different that we haven't measured yet because too many things have
features in the same place. Like that 2.42 feature, even though nothing
else that we have in our labs match the CN position there are clays and
even some organics that have absorptions near there but not exactly
there. So it's very disconcerting until you match it exactly.

And this kind of stuff has plagued spectroscopy for many years. For
example, the SO2 discovery on the volcanoes on Io, Jupiter's satellite,
it took a huge, huge effort to figure out what - it was 4 micron band,
4.03 microns, to figure out that that was CO2 because the spectra hadn't
been measured for that compound in that wavelength range. So it's -
there's just too many compounds to measure and too little funding to get
it all done very quickly. So even though we've been working at it for 30
years we're still working at it.

So anyway, though, the interesting part is we have many absorption bands
in both Phoebe and Iapetus that are in common. So the only thing that
isn't in common is the xCN step. It shows a little bit in some Phoebe
spectra but not as well as it does in Iapetus and the blue upturn in the
Phoebe spectrum is different. And if that was explained by this Rayleigh
scattering due to dispersal and ice, it could completely explain the
spectrum that the stuff on Phoebe and the stuff on Iapetus is the same
material.

We know, to some degree, at least some of it is the same. We don't know
if all of it is the same yet. So it's still an open question on what's
coming from where and we're continuing to address that.

Man: Quick, a quick question; so would you say these are not simple
nitriles then; these would have to be more complicated, more complex,
higher molecularly?

Dr. Roger Clark: No, they actually have to be simple because as you get
to more complex materials it - you get more absorption bends and, in
fact, the Iapetus spectrum here, look at the four, well, 4 all the way
out to 5 microns there's a lot of little structure there. That's not
noise. That's real. It's all real and even go over and look at the 2.42
band and just short of that, let's see, what wavelength is that; about
2.2 microns there's a little teeny dip; even that's real. Essentially
everything in the spectrum is real. And we can't explain most of it.

Man: Well - well, if it's, I don't understand. If it's not a simple one,
I mean, you know the spectra of that, why would you not conclude it's
not a simple nitrile, then?

Dr. Roger Clark: No, it has to be a simple nitrile.

Man: Yeah, right, but...

Dr. Roger Clark: Because a more complex one would have other absorption
bends that would occur where we would detect them and we don't see it.

Man: Right, but I guess you said you're not even certain so, I guess...

Dr. Roger Clark: No, the nitrile does match exactly. It's a nitrile
that's unique to nitriles and so it has to be a nitrile, okay?

Man: Right.

Dr. Roger Clark: For example, let's see, like, blue nitrile rubber
gloves...

Man: Mm-hm.

Dr. Roger Clark: ...that's an organic compound that has a CN attached to
it. Nitriles, by the way, are very, very tough materials. The blue
nitrile rubber glove has huge absorption bands in the 3.2 to 3.4 micron
region; somewhere in there. I forget exactly where. Huge absorptions
that are bigger than the nitrile band and so we would detect it. And the
spectra of Iapetus and Phoebe are pretty smooth through there so there
can't be much in terms of these complex organic compounds. It'd have to
be a pretty small amount, okay?

Man: Thank you.

Dr. Roger Clark: Okay. Let's see, going to slide 17, so here's a summary
between Iapetus and Phoebe. So we have the cyanide compounds, the 2.42
and the 4.8 micron features. We have the trapped CO2 that looks the
same. We have bound water and trace organics that appear similar. So
far, and we haven't gotten our good look at Iapetus but, so far, Phoebe
has more diversity in the compounds and the, you know, like the nitriles
are a pretty strong feature on Phoebe and not on Iapetus. We also, what
I didn't show in the last spectrum, Iapetus also has CO2 frost; that's
free CO2 as an ice, dry ice, and we didn't detect any of that on Phoebe.
So we only had a distant fly-by on that one Iapetus fly-by so September
of next year will give some pretty definitive data. It's looking to be a
very, very spectacular fly-by.

Man: How close is it?

Dr. Roger Clark: We're looking at changing it right now. I think
currently it's, like, around 1500 kilometers and we're looking to change
it to about 2000 kilometers. The advantage is it'll give us an hour more
time close in over the dark material. So we'll be able to do a much
better job on it even though we're a little bit further way. Observing
time close in is a very precious resource so sacrificing a little bit of
spatial resolution for the more time will be a big help to the science,
okay?

Man: And, while you're on Iapetus, is there any reasonable explanation
yet for the ridge?

Dr. Roger Clark: I have not heard one.

Man: Okay, thank you.

Dr. Roger Clark: Yeah, I haven't actually - I've been too busy with the
other stuff but I haven't heard anybody talk about it much yet.

Man: A lot of people ask about it, that's why I'm akking

Dr. Roger Clark: Yeah, I'm sure. I did hear something recently about a
ring; that it might be a collapsed ring.

Man: Mm-hm.

Dr. Roger Clark: But I heard that second-hand. I didn't hear that actual
talk. Okay, so on to Hyperion, the sponge moon. And Hyperion is
interesting. This is slide 18. It's very odd how these craters look. It
looks like it's been degassed and that this is the residual material
that's left. It's mostly water. It's like dirty water ice. So let's go
to slide 19 and this, again, the imaging system and VIMS did resolve
enough to get a few pixels on the bottom of these dark crater floors.
The - interesting in this picture is there's no small craters. They've
kind of been eroded away or probably buried or something but that's a
big mystery and then why the crater floors are dark is also a mystery.

Well, the next slide shows the spectra; the dark areas in blue there are
the dark crater floors and we do have a couple of noise spikes to ignore
and that's at 4 microns and 4.8 microns. So ignore those things. We have
a 2.42 feature, just like on Phoebe and Iapetus. At the bottom of the 2
micron band we see the structure that shows the bound water bands and we
have a CO2 band out there at 4-1/4 microns. So, again, same basic
compounds. So the CO2 is trapped the same way. We have the same bound
water and the same 2.42 feature. So, again, it's showing at least some
commonality in the main dark material in the system.

Let's go on to slide 22. I said I wasn't going to mention Titan. I think
you have had a talk on Titan. Have you had a talk on Titan's surface? I
promise I'll do one on Titan's surface.

Trina Ray: Yeah, we had Larry Soderblom give us a talk on Titan's
surface.

Dr. Roger Clark: Okay.

Trina Ray: So we're good.

Dr. Roger Clark: We have lots of controversy on Titan's surface because
the atmosphere is so dense and blocks so much of the spectrum it's very
hard to understand the composition and we're just starting to get
handles on it and you saw some indications of that from Larry. But we
are chipping away at it and making some progress and I think we'll have
some good stuff coming up here in the next year.

So let's go on to Rhea.

Man: Do you believe, by the way, that the lakes are lakes?

Dr. Roger Clark: Well, it turns out that VIMS can actually detect liquid
methane and liquid ethane down to millimeters and thickness and I did
present at the BPS where we are detecting some of that. We have not had
a good view of these lakes, though they sure look like lakes. Whether
there's any liquid in them now, gee, I'd sure like to get VIMS over one.
But we haven't had that opportunity yet. So, hopefully, we'll get one
soon and be able to say something.

Okay. So on to Rhea. Rhea is one of the bigger icy moons in the Saturn
system. It's got these light, wispy streaks so there's some variations
on the surface but, if we go to slide 23, for what we resolved in our
one fly-by all we see is ice. We don't see anything else. This one
spectrum here it's a little funny in the 1 micron region because it's
the old calibration for that region. But, ignoring that, we don't see -
we see just a teeny, teeny trace when you really zoom in of CO2. But we
don't see any hints of this 2.42 feature. It looks like pretty pure ice.

So I'm going to go on to Dione. And Dione is much more interesting and
that's a large part of the focus of the paper that's about to go to
Icarus. In this slide 24 here you see that there's these wispy streaks,
which, you know, nobody knew what they were after the Voyager encounter
and now the Cassini imaging team has resolved them quite nicely to be
geologic structures, cracks and, perhaps, faults on the surface of
Dione. And so huge cliff walls are exposed where the ice is showing up
as bright. And VIMS resolves these, at least to some degree, and
confirms that the bright nature of them is pretty pure water ice.

But, around those, especially on the trailing side and that's the side -
the trailing side is - when the satellite is moving around in its orbit,
it's the side that's behind, you know, so if there was - if you were in
a car it would be the bumper, or it would be the trunk of the car
driving down the road.

So it's a little darker on the trailing side and that dark material is a
focus of our study. So, let's go to slide 25 and this is the VIMS best
resolution data for that fly-by so that's about 1/40th or so of what the
imaging team can do. So this is a mosaic of many frames and what is
interesting here is, let's see, if you go to slide 26 you see that the -
you see the terminator and the direction of sunlight is from the lower
right but look at Crater A, for example. Crater C is a little harder to
see because it's kind of bright there and some of the others you have to
stand back from. But Crater B, Crater A is probably the best thing to
look at. Crater B is dark on the left wall and bright on, excuse me, I
got mixed up there. Yeah, bright on the left wall, dark on the right
wall. But the direction of sunlight would say it should be just the
opposite. So it's not a lighting effect. It's got to be dark on that
right side because of the material there and not the lighting.

Man: Comment?

Dr. Roger Clark: Yeah.

Man: Yeah, I notice that if I squint my eyes you can see that effect a
lot better.

Dr. Roger Clark: Or move back about ten feet.

Man: Okay, thank you.

Dr. Roger Clark: Let's see. Okay, so - so now go to slide 27 and this is
a map of ice strength; so it's the strength of the 2 micron ice bend
which, again, can be due to one of two things; composition abundance or
the grain size of the ice. And, in this case, by analyzing multiple ice
bands it's mostly due to the abundance of the ice or the amount of
contaminants of the dark material.

So looking at, let's go to slide 28, and look at Crater A. On the right
side of the inside of Crater A on the wall there it's dark, meaning low
abundance of ice and on the left side inside the crater it's bright,
meaning high abundance of ice.

Now Crater C you see the same effect and Crater B is kind of too bright
to see. Crater D shows the same effect. It's dark on the one side and
bright on the other. All of this implies that material has been coming
in from the trailing side, coating the surface as a uniform, you know,
rain of material coming down. So it is arguing that the material on
Dione is external to Dione itself. So if the stuff on Iapetus is
similar, then both Iapetus and Dione are arguing for an external source
to the dark material.

Now, let's see. I'm now looking at the spectra in slide 29. It does help
back there on 27, 28 to bounce back and forth and then bounce back and
forth between, like, 25 and 27 and see the differences in the lighting
versus ice abundance, if you want to toggle that a little bit. So then
to slide 29 we see the spectra and the spectra have a couple of
interesting properties. In the darker regions we see the 2.42 micron
band, a trace amount of CO2 but notice compared to Phoebe and Iapetus
and even Hyperion, for that matter, both the CO2 and the depth of the
2.42 micron feature is much weaker. So while there's some dark material
there it's a less amount of dark material.

Then the other thing that's interesting to note is that the, as you go
to shorter wavelengths, the plots go up, meaning it has that peak in the
blue, sort of like Phoebe. So, again, is this due to a ferrous iron
absorber or is this due to the Rayleigh scattering of small particles
disbursed particles in the ice. I'm kind of intrigued by the idea of the
small particles disbursed in ice and we're trying to look at the
distribution of these effects over the whole satellite and see if we can
prove that or not. And, so far, we haven't completed the study so I
don't know what the answer is.

Let's see, so I'm going to skip Tethys and Mimas. We don't detect any
dark material on those so the ice is even purer. Here's that trend as
we're getting closer to Saturn the ice on the surface is getting purer
and we do detect very, very trace amount of CO2 on Tethys and Mimas but
even smaller than on Dione.

Man: Quick question about Dione, though, before we leave.

Dr. Roger Clark: Okay.

Man: What about the crack? Now this moon is dead now, right? It's not
geologically active and what caused them in the past?

Dr. Roger Clark: Well, that's a good question. We don't know if it's -
it's certainly not as, you know, active like Enceladus is. But there's
still suspicion that it may be contributing to the, you know, material
out from it to the e-ring. And there have been some almost detections
where we could almost say yes or no but the scattered light issue is
difficult and we can't - haven't gotten good enough data to make - give
a definitive answer yet. So there's been some suspicions but nothing
that you can prove anything by yet, okay?

Man: Thank you.

Dr. Roger Clark: Okay, so on to Enceladus. Probably everybody on the
phone knows that Enceladus is active. So we've - one thing that Cassini
has confirmed is that it's geologically active and that it's a major
source of material to the e-ring. The e-ring is mostly ice so Enceladus
is spewing out mostly ice and the next slide, 31, shows more of these
cracks; cracks that, you know, on a small scale Dione has these but
Enceladus has them a lot more, kind of more evidence that Enceladus is
more geologically active than Dione is or was. So if Dione was or is
still doing things, it's probably much less and that's what the data is
showing so far. If it is active, it's at a very, very small level
compared to Enceladus.

Next slide is slide 32. One of the more interesting things, I think, is
the craters look soft, much like on Hyperion. So on a fine scale,
whenever we've gotten close to these and this is true for the small
satellites, that there doesn't seem to be a lot of fine structure like
the fine structure is buried and it's probably buried in a fine dusting
of ice particles. And is that - what we don't know yet, is that true
throughout the Saturn system? As we get more and more close-ups, maybe
we'll extend that trend everywhere. Like, at Phoebe, we did see fine
detail but in the inner satellites there seems to be more of this stuff
coating things.

So, our initial look, going to slide 33, was that Enceladus was just a
beautiful ice spectrum; this - all these dips here are all due to water
and just a gorgeous spectrum, matches lab data very nicely., because of
these smooth areas that look like flow features, people have thought
that the only way you can do that is have an ice ammonia mixture to
reduce the freezing point of the water by as much as 100 degrees Kelvin
and that would allow these ice ammonia mixtures to flow and give you
cryovolcanism. But, so far, through many attempts from, both from Earth
as well as VIMS, we've never detected any ammonia. And so it's still -
so it just makes it more curious what's driving the system and how does
it keep active?

Man: What about organics? I've read that - a lot of claims that there's
organics there.

Dr. Roger Clark: Yes, there has been detection of some organics by the
INMS. Did Hunter give a talk on that? Was that on Hunter Waite on...

Trina Ray: Yeah, Hunter gave a talk but only on Titan.

Dr. Roger Clark: Okay, okay. I think it might be published now that INMS
has detected some organics coming out of the Enceladus plumes. I don't
believe but I don't know for sure but I don't believe that organics
would depress freezing points, at least not like ammonia does. Ammonia,
the NH is a nice polar bond and when it mixes with water you get, you
know, NH3OH, and that really changes the chemistry of the system. And
I'm not an organic chemist but I don't think, at least most organic
molecules, the simple ones, you could do that kind of stuff.

So, let's go to slide 34. Of course, everybody's seen the geyser plumes.
VIMS did get spectra of these plumes. They're pretty low, you know, low
signal so - but enough to see that the plumes have ice signatures in
them and we're hoping to get some better spectra on some upcoming
opportunities.

So, next slide, slide 35 shows maps of the ice strengths and in the
South Polar region, in the upper left, shows the ISS reference, so you
see that this view of the South Pole with the tiger stripes. And the
tiger stripes have a heat source there and what happens when you have
snow and a heat source is the snow grains actually increase in size with
time. If you live in a cold climate, like I live in Denver, on a very
cold winter day we'll get a very fine powder snow but as - after a
couple of days as it warms up that snow turns to a very granular texture
and a large part of that is grain growth due to the temperature. As the
temperature goes up the water molecules evaporate from the corners of
crystal edges and they impact on crystal faces and the grains tend to
grow.

And it's a well studied phenomenon and well predictable so in the South
Polar region that's exactly what we see that the ice absorption gets
stronger in the tiger stripes where the heat sources are and the grains
grow pretty much like predicted. And VIMS has a paper; one of the papers
submitted to Icarus will be on the subject.

Okay, next slide, so these just show, let's see, I'm trying to, let's
see, okay. So these just channel, or slide 36, shows the spectra that
shows the changes in the ice bands in the tiger stripes and between
them. It just shows a couple of the ice bands that are very sensitive to
grain size and the bottom curve in the tiger stripes, the curve is lower
but the bottom of the absorption band is flattened and that flattening
actually tells us when we run a model of the spectrum of ice we can pin
the grain size pretty nicely by that and by the shape of that spectrum.
And, in this case, it tells us it's on the order of a couple hundred
microns or .2 millimeters in diameter, average diameter. So it's remote
sensing at a distance on a very fine scale.

Next slide; there are some areas on Enceladous that have CO2 but most of
the areas do not; the global average and the black line, we're on slide
37, does not show any CO2 but a few areas do show some nice CO2
absorptions. And, again, these are CO2 that is trapped, not free CO2.

Slide 38, so this shows a summary of the CO2 detections and it shows at
the bottom you see Iapetus appears twice and you see that the CO2 band
changes position. That long position, the very bottom Iapetus one, is
the position of CO2 frost and the shorter wavelengths are positions of
CO2 trapped in other material. And notice that Dione and Iapetus have a
shorter CO2 band than, like, Iapetus and Phoebe. Did I say that right?
Dione and Hyperion, the two green lines, are shorter. So maybe that's an
argument that the composition is different or maybe it's just an
indication of some other condition of the CO2 that may not be related to
the overall dark material mineralogy.

But we do have a trend here going from the largest CO2 bands are in the
outer satellites and, as we move in to Tethys and Mimas those are about
the same. As we move in the CO2 bands are getting smaller so the ice is
getting purer. Same with the dark material.

Okay, now to Saturn's rings so that's the last stop in solid surfaces in
the Saturn system. The problem with Saturn's rings is they're real close
to Saturn and that causes a lot of problems with scattered light and
this slide illustrates the scattered light problem.

In slide A is a false color infrared image from VIMS and slide B in red
shows the methane band strength and the red shining on the rings there,
where the rings are reddish in color, shows the intense scattered light
from Saturn hitting the rings.

So we found that, well, when we were going in we didn't realize how bad
this problem was. We knew there was going to be some effect but VIMS is
such a precise instrument we're finding that we can see the scattered
light most places in the rings. So the best place to look is on the
night side of Saturn so that we only have a problem with thermal
emission from Saturn and so, depending on distance from the rings, we
can or can't use the 5 micron region. But most of the spectrum is clean
because the night side of Saturn is actually dark.

But look where it's labeled, figure B is labeled shadow and along the
shadow edge it's red. That's light shining through Saturn's atmosphere
being refracted and right at the shadow edge, that's where sunrise or
sunset is and you see light through the atmosphere. So we see absorption
bands through Saturn's atmosphere on the rings right there and when we
actually went into Saturn orbit insertion in July 2004, Cassini was
looking down right near the ring shadow there. And in the C ring we were
actually looking in the part of the shadow where Saturn light was
refracted onto the rings. And we initially thought we had discovered a
lot of organics in the rings but it turned out to be this scattered
light problem.

So we found that the best place to study the ring spectra and the
composition of the rings is just outside that area; that, on the - near
the shadow but not too close that we're in that refracted zone. So,
we've had to change a lot of our observations to target that area and,
as the mission goes on, we'll get more and more opportunities to look at
that area and get better spectra.

So, if we go on to slide 40, it shows the spectra of Saturn's rings.

Man: So this conjunction must have been a gold mine for you.

Dr. Roger Clark: This what?

Man: This conjunction that we just had about a month ago. It must have
been an excellent data opportunity.

Trina Ray: The (REV 28) occultation and conjunction? It was fantastic.
We're hoping to have a talk on that next month.

Man: Okay. But, I mean, that must have been especially favorable for
your instruments, right?

Dr. Roger Clark: We've had, lately, some very good opportunities to
observe the rings and as we crank up out of the - from the plane of the
rings to higher orbits, we get to look down on the rings and we'll get a
lot of good spectra and there's a lot of interesting stuff coming out on
the rings. And the first part of the mission, for me at least being a
solid surfaces person, I've been dominating my time on the satellites.
And now I'm finishing up those papers and I'm going to start working
more on the rings. So, yes, I'm looking forward to that. And, to get
into the data we've already gotten which I don't get much time to do.

So, let's go to Slide 40 and these spectra are just text book spectra of
pure water ice. We have not detected any CO2 at all. We've had some
trace hints but we haven't been able to confirm them. It's been so weak,
any signature basically at the noise level. So if it's there, any CO2,
it's extremely weak. The - most of the rings are very pure. The bright A
and B rings we've detected nothing but ice. In the interior of the
Cassini division it is more dusty and there we do see features that sort
of look like Phoebe and Iapetus but we have not detected the 2.42 band
and here you see the C ring has - is going down towards shorter
wavelengths and that is a little bit of the dark material but not enough
to show us if there's a 2.42 band there and not enough to see a CO2
absorption.

If we go to 41, one of the problems with detecting things besides ice in
the rings is how dark they are and this illustrates that, you know,
we're on slide 41, it shows a spectrum of Dione and Dione, in the long
wavelengths, is 3% reflectants. For reference, carbon - charcoal and
carbon black is around 1-1/2% reflectant through this whole range and in
the visible. And so you see that, like at 4.5 microns, the rings are
many times darker than the darkest carbon material. So water is very
absorbing in the infrared and it's very difficult with such low signals
to see if any CO2 is there at the CO2 line position as shown. But even
in our best data, averaging lots of spectra together, we have detected
no CO2.

So, so far, the rings are the purest. We have detected and did I include
that? Yes, okay. Next slide, 42, the F-ring is an extremely interesting
ring and it shows a gorgeous 2.42 micron feature. It doesn't show any
CO2 and it shows the structure much like Iapetus so, in the visible, you
know, toward 1 micron there. So it looks like material from Iapetus
minus the CO2 and it has a new absorption at 2.85 or so, that major dip
there just below 3 microns, that appears to be, in this spectrum, it's
partly a transmission through the rings and that's partly due to
structure in the water ice spectrum that you normally don't see. So it's
a scattering effect. So that isn't a unique identifier of something else
but that 2.42 micron feature and - is really quite unusual.

So, we're seeing that throughout the whole Saturn system now. We see it
from Phoebe, into the F-ring and then why is the F-ring so dirty and
then it's suddenly clean inside the F-ring? So it's like the F-ring is
batting clean up for the dust, you know, and dirt in the system and,
even though the E-ring is pure ice, and the F-ring still has a lot of
ice in it, but why is everything else so pure and the F-ring so dirty?
We don't know.

And, with that, I'm going to go to slide 43 and, let's see, slide 43
just summarizes what VIMS has found so far. So from the very out -
outside, Phoebe through Hyperion, we have a fair amount of dark
material, CO2 and the possible CN compound and then as we get in closer
to the rings, things get purer.

So, from that, then we go to conclusions on slide 44 and, again, it's
the 2.42 micron feature, which we're really beating our heads on whether
it's a cyanide but it's pretty common throughout the system. We have the
CO2 common throughout the system but this nice trend of purity as we get
closer to the rings.

And, with that, I'll take questions.

Man: Question?

Dr. Roger Clark: Okay.

Matthew: This is (Matthew) at the Saturn Observation Campaign. It seems
to be, especially when you're detecting this cyanide on these outer
moon, that if you could take a moon like (Unintelligible) and move in
toward the inner solar system, basically, it would be a comet. Am I
correct in this?

Dr. Roger Clark: Well, cyanide compounds aren't necessarily volatile,
you know, like a blue rubber nitrile glove is not a volatile so it
depends on the exact form of the cyanide and until we get an exact match
we really won't know. We know it's not hydrogen cyanide. The hydrogen
cyanide absorption is at 2.5 microns.

Matthew: Okay.

Dr. Roger Clark: So we know it's not hydrogen cyanide.

Matthew: I've read that they recently detected some kind of cyanide
compound on this comet Swan. I'm not sure if it's the same or...

Dr. Roger Clark: Yeah, I think they're detecting HCN.

Matthew: Oh, okay. Thank you.

Dr. Roger Clark: That's what's been commonly detected in comets, at
least.

Matthew: Alright, thank you.

Dr. Roger Clark: In the inner-stellar medium there are quite a number of
cyanide compounds, have been discovered; they've been discovered at
microwavelengths where they only need a few molecules synthesized in the
lab to test it and so, like, hydrogen cyanide is HCN, there's HC3N, HC -
HC5N, HC7N, all the odd numbers and we're trying to get a hold of some
of those compounds in enough abundance that we can measure a reflectant
spectrum and we need a couple of grams and it's very difficult and so
far we haven't been able to get them. So that might be a source of
cyanide compounds that might match but, you know, we don't know yet 'til
we do it.

Trina Ray: Are there any other questions?

Man: How about a question about Hyperion? What is the cause of those
sponge-like appearance? Any clue?

Dr. Roger Clark: Some people have speculated that maybe Hyperion was
full of other volatiles like maybe ammonia or something and it all
evaporated away and so it left this sponge-like stuff. I mean, it sounds
plausible. I don't know. I haven't seen a definitive paper that, you
know, provide a "This is the argument and it's the only argument" type
so, hopefully, we'll see that here. I think the Imaging Team might have
a paper on the subject being submitted to this ICARUS special issue.

Man: It's just so unique. I mean, I guess, if that was the explanation
maybe there would be other moons like that.

Dr. Roger Clark: Well, yeah. In fact, that's what's so bizarre about it.
Why, I mean, that's been one of the surprises in the solar system. We
see so many different things and, yet, why don't we see, you know, more
things in common like that? You know, we've seen up-close comets and
they don't look like that. So it's very unusual.

Man: That relates to my question. It has to do with the purity of the
water ice that you're seeing. Is that because of lack of processing or a
recent origin or what's the predominant theory on that?

Dr. Roger Clark: Well, let's see, most of the satellites are pretty
abundant in water from their densities typically 1.3 and ice is 1.0 and
rock is, you know, 4.0 or 5.0. So the abundance of water, if you did a
rock water model, would be dominated by water. So one would expect them
to be mostly water and the question is, you know, while we do see a few
other materials from the cosmo-chemists, in particular they want to see
ammonia, why don't we see ammonia?

And is it a surface effect that just the small amount of ammonia that's
been on the surface has evaporated away so we're seeing the residual
pure water surface or what? But this trend of a lot of water in the
outer solar system we've known for a long time; from Earth-based
spectroscopy, we've known the Galilean satellites, the Saturn
satellites, Uranian and Neptune satellites all have a lot of water ice
exposed on the moons' surfaces.

And why that is is not really known. And why we don't see a lot of other
stuff that's been predicted, at least we are seeing the CO2 that was
predicted a long time ago and for a long time nobody saw. And we
couldn't see that CO2 line from Earth-based telescopes because CO2 in
our atmosphere blocks the view.

Man: Thank you.

Man: You didn't do the tiny moons for a lot of obvious reasons. Any
general comments you can make about them?

Dr. Roger Clark: Well, the innermost moons, so far, the spectra that
we've looked at look like pure water ice. We haven't gone in and done
detailed mapping of resolved stuff on the moons; that'll be after we
finish the main satellites.

Man: Oh, they haven't been doing them; oh, I see.

Dr. Roger Clark: We have some data but we haven't analyzed that data for
that stuff yet. Too much to do.

Man: Mm-hm. Is there going to be - when's the closest fly-by of Dione,
if any?

Dr. Roger Clark: We've had our close fly-by of Dione and that's the data
that I showed here for VIMS; that's the best data that we will get in
the tour. We may get more in the extended mission, depending on how that
plays out.

Man: That's what I was wondering.

Dr. Roger Clark: It's on our desired list.

Man: Okay. Very good, thank you. Excellent.

Trina Ray: Okay. Are there any more questions? Okay, well I'd like to
thank Roger for joining us today. We really appreciate it. We
understand, you know, all these scientists on Cassini are very busy and
we always appreciate it when you can take an hour to talk with us.

The next (CHARM) telecon is tentatively the (REV 28) occulation data.
We've had some spectacular data that was taken on the rings and Saturn
itself while the sun was behind. Again, we don't have a CHARM telecon in
December. That's a free month. And then when we start in early next
year, some of the things we'll be talking about will be the dunes on
Titan, when the Hyperion special issue comes out, we'll see if we can
get a couple of Icy Satellite scientists to come talk to us about
Hyperion, maybe do a navigation tutorial. Those are just some of the
things that are on tap for early next year.

And, with that, we'll see you all in one month on the last Tuesday in
November. And have a great month.

Dr. Roger Clark: Bye.

Man: Bye, see you all next month.

Man: Bye.

END