**FTS-NASA-VOICE**

**April 26, 2005**

**1:00 p.m. CDT**

Coordinator Thank you all parties for standing by for the conference
call today. Today's conference call is being recorded. If you have any
objections, you may disconnect at this time. Please be aware of
background noise, for all lines are open today. I'd like to turn the
call over to your host for today, Ms. Trina Ray. Ma'am, you may begin.

Trina Thank you. Well welcome everybody to the CHARM Telecon for April
of 2005. We've got a terrific topic for you today. We did a targeted
flyby of one of the moons of Saturn Enceladus, which is terrifically
interesting. We actually have two presentations today. Marsha Burton
who's with the Magnetometer Team here at JPL, she's actually the
magnetometer investigation scientist, will be talking a bit about what
the magnetometer instrument saw, as we flew by Enceladus, it was a
pretty close flyby. And Dr. Elizabeth Turtle, who's an associate of the
Cassini Imaging Team, will also be talking today about some of the
really, really interesting surface features that we see on Enceladus.
It's just more mysterious every day that we look at it. It's pretty
terrific.

The files have just been loaded up to the Web site recently, so if you
haven't downloaded both sets of files, there's a mag file and an imaging
file for today, be sure to go off and download those files. We're be
doing the mag presentation first, and it's probably going to be about 15
minutes, maybe 20 and then the imaging presentation will be after that.
We have the telecon line for the full two hours and we can go as long as
there are questions, it shouldn't be a problem. I thank both of our
guest speakers for being with us here today, and I'll turn it over to
Marsha Burton. Marsha, go ahead.

Marsha Okay, thanks, Trina. So hopefully you pulled up the package, I
provided it in PowerPoint and PDF. I've got a little audio file at the
end of the PowerPoint that hopefully made it with the PowerPoint
presentation. So if you have your choice, you might want to get that
one.

So I'm going to talk about the recent flybys that we had of Enceladus.
Just kind of a few preliminary remarks. You know there are a lot of
interactions of bodies in the solar system, be it planets or moons with
the plasma surrounding them, and we're familiar with some. I mean
certainly the supersonic flow of the solar wind impinging on the earth,
which has a strong magnetosphere, you get certain features forming like
bow shocks and a strong magnetosphere and that deflects the plasma
that's flowing around it. Then there are interactions, such as the type
with the solar wind interacting with Venus. Venus doesn't have a strong
magnetic field, so actually its ionosphere acts as an obstacle, to stand
off the solar wind. So there are all kinds of interactions.

Our experience with the Galileo Mission at Jupiter provided a whole
other kind of plasma interaction with bodies in the solar system,
because that type of flow, in a planetary magnetosphere, is what they
refer to as sub elphanic, it's no longer flow that's dominated by the
thermal energy of the solar wind, it's really dominated by the magnetic
field. The types of interaction that characterize the bodies interacting
with plasma in Jupiter was very different from what we see around the
Earth or Saturn or Jupiter.

Also, the interaction is dependent upon the characteristics of the
bodies. At Jupiter we found there were moons with intrinsic fields or
fields that were induced. Europa was very interesting, because they
speculated it has a subsurface ocean, which is conductive and therefore
it can have a magnet field induced in its interior. So there's all kinds
of different plasma interactions with satellites in our solar system. So
that's just a few preliminary remarks about that. And that's kind of
just to point out that each one of these interactions is like a little
plasma physics laboratory for scientists. A lot of the features
necessarily are very complicated and little bit difficult to describe,
so it's a bit tricky.

But anyway, we've had a couple of close flybys of Enceladus, on the
second view graph I provide a few facts about the moon. It has a radius
of 250 kilometers, and then just some of the parameters about the E3
flyby that occurred in February, on February 17^th^, and it was at an
altitude of almost five body radii. Then E4, a month or so later, which
was substantially closer, less than two body radii. E3 occurred in the
Northern Hemisphere, which is important for understanding the
magnetosphere interaction and E4 in the Southern Hemisphere.

What the magnetometer has seen on a number of the orbits, in fact
throughout the whole inner magnetosphere are what we refer to as ion
cyclotron waves. An example of those is shown in the third view graph,
they're really distinctive features and they're basically oscillations
of the magnetic field that occur, when neutral atoms, for example if a
neutral was produced from Enceladus' surface and then ionized, it can
start to spiral around the magnetic field and it causes oscillations
that are called ion cyclotron waves. We've seen throughout the inner
magnetosphere, as I mentioned, but really predominately near Enceladus.

One can do a power spectra of these waves, an example of this is shown
on figure four, and this is just looking at the power in the waves, as a
function of their frequency. You can determine what ion species are
present and causing the perturbation. So one particular example of that
is shown in slide four. Are there any questions so far?

M I have a question. When you're talking about the ion cyclotron effect,
is that due to the magnetosphere of Saturn or the magnetosphere of
Enceladus?

Marsha Well the predominant effect throughout this entire region is
Saturn\'s magnetic field. I mean it's rather strong. You'll see at the
orbit of Enceladus, it's on the order of 300-nanotesla or 400-nanotesla,
a nanotesla being a unit of measure; the earth's surface field is
something like 30,000 nanoteslas. So it's a fair fraction of that value.
So any magnetic field created by any of these satellites, unless we're
really surprised, is going to be much weaker then that. So basically
these particles are spiraling around Saturn\'s magnetic field line. And
it's basically a dipole field, just like Earth's. I mean it has other
higher order terms, but it's basically a dipole field.

M Thank you.

Marsha Okay, so slide five shows what we can do to the data. This is
what we refer to as the dynamic spectra. So it's basically just doing a
power spectra, as a function of time, and color coding it to show the
amplitude of the power. So these, again, point out the ion cyclotron
waves and this is a dynamic spectra in the vicinity of the second
Enceladus encounter. You can see the vertical line indicates where
closest approach is. What we found was, like I said, even though we do
these throughout the magnetosphere, because they're probably due to
water products, we see them predominately near Enceladus orbit.

Let's see, what else do I need to say about this? Oh, the frequency is a
function of the magnetic field. So you can see that as you get closer to
periapse, which is kind of towards the center of the plot, the frequency
is shifting, and that's why that occurs. But they really occur ---
predominately, near Enceladus is where we see them.

Some of the scientists on our team, I should point out that there are
really kind of a couple of groups of people that are working on this.
I'm not working on this, I'm just kind of presenting results from some
of our team members who are at a scientific meeting in Europe right now,
and there's a group of people at UCLA that are doing some modeling and
there is also a group of people in Cologne, Germany, Co-I's of ours that
are doing modeling.

They can use these ion cyclotron waves, again with a lot of simplifying
assumptions to estimate what sort of production rate of ions, how many
ions per unit time you would have to produce, in order to get the
signature that we're seeing. One of the scientists at UCLA has estimated
that you'd need something like 125 kilograms per second to see the waves
that we're seeing near Enceladus.

Then just to show you a little bit of our data, the next, slide six
shows the coordinate system that we plot our data in and it's basically
a moon centered coordinate system. So we have the X axis along the
direct of co-rotation, Y is to the planet and Z is aligned with
Saturn\'s rotation axis.

The following plot, some people like to look at images, but we like to
look at time series of magnetic field data. So the magnetic field, of
course is a vector and slide seven shows the components of the vector
plotted from the February 17^th^ flyby, and again in this coordinate
system that I just described. You can see that the field is roughly
300-nanotesla and the magnitude is relatively constant on this scale,
but there are significant perturbations in the X and Y components. You
can also see, quite predominately, in the X and Y components, these ion
cyclotron waves that I talked about.

The next slide is a similar plot, showing data from the March 9^th^
flyby. So I know that it really takes a lot of experience looking at
these plots to figure out what's going on. So I plotted the data in a
different way and on slide nine, you will see the magnetic field vectors
projected onto the X/Y plane and then there's a schematic over to the
right, sort of depicting the direction, the orientation of the
coordinates. So the X axis, again, is along co-rotation, so that's the
direction we're moving and the satellite is moving. To the right is
Saturn and the blue line kind of depicts the expected draping of the
magnetic field.

What happens when the magnetic field encounters a body, an obstacle, the
field line, in the case when mass is being loaded, or added to the
magnetic field, the field lines drape around the obstacle, in a
characteristic way. That schematic is shown on the right side and the
actual vectors that we found from the February flyby and the March flyby
are plotted too.

The February flyby, you can see that there is relatively small
deflection in the magnetic field; the draping signature is much less.
But then when we get closer, during the March flyby, you can see that
the draping signature is much stronger and in fact at closest approach,
the vectors, of course are proportional to the strength of the field.

Trina So Marsha, I just want to make sure that I understand, on the
right hand side, the blue lines go up and down, but really you should
imagine it, it should be sideways, right? Because if we're looking down
the left hand side ....

Marsha That's okay, we're looking down on the equator, down from say the
North Pole, down on the equator, in this projection. So you should see
the field lines drape around the body. The characteristic way, the
amount of draping that occurs, all these things give scientists
information about the amount of mass that's being added to the field. So
that's one thing, then the additional enhanced magnetic field that you
can see right in your closest approach during the March flyby, is
another thing that we weren't expecting to see. So this enhancement of
the field, when we're closer to the body is what got people interested.
Maybe there was another signature, possibly a signature from the
interior of the satellite.

So then a projection onto the Y/Z plane is shown in slide ten. So in
this view, the Z axis is up towards Saturn\'s North Pole and Y is
pointed towards Saturn. Again, the characteristic draping that you would
see in this orientation is shown on the right hand side. So again, the
February 17^th^ flyby, you see very little signature of draping and in
the March 9^th^ flyby, you do see the field line draping, and again, you
see this enhancement, indicated by the longer magnetic field vectors at
closest approach.

So this really peaked our interest and really kind of indicates that
something is going on, more than just a body without an atmosphere, an
ionosphere and internal field. So scientists on our team, again, these
are people that are working at UCLA and at the University of Cologne,
are thinking that the most plausible explanation for this field line
draping signature, is the loading of the field lines by material from
the moon's surface. So this would be an atmosphere that gets ionized and
that's what's presenting this obstacle to the flow and causing the
magnetic field lines to bend. So since gravity on Enceladus is small,
there would have to be some kind of continual replenishment of the
source, and people have speculated for years about ice volcanoes or
geysers.

So on to the final view graph, just to summarize what we've seen, it's
basically the combination of the field line draping signature and the
predominance of ion cyclotron waves, near Enceladus that have caused us
to think that there's something going on in this body. And in fact,
we've asked the project to change the planned trajectory, and go closer
to the planet. It's really important to get closer to the body, to
understand the signature, and they've agreed to do that. In July of this
year, we'll go within 200-kilometers; I'm not sure what the current
altitude is now.

Trina It's 175.

Marsha It's 175?

Trina Yes.

Marsha Okay, so 175, which is great, of Enceladus' surface, so we can
hopefully detect more about what's going on in the interior, whether it
be an atmosphere or even something like a subsurface ocean, like Europa
has.

Then at the final, if you have the PowerPoint file, maybe you don't want
to do it now, but ....

Trina But actually, Marsha, it's not even working with the PowerPoint
file. I think you're going to have to send the wave file independently
and we'll load it later. But if you could tell us what we'll hear when
we listen to it later, that would be great.

Marsha Yes, it's really cool. I mean we've probably all heard the RPWS,
the plasma wave audios, so we've done a little audio of these ion
cyclotron waves and they're really, I don't know how to interpret them,
but they're really kind of interesting to listen to.

Trina Can you play it over the phone by any chance, like hold the phone
up to the ...?

Marsha You know I can try. I actually did a test, Trina, and I sent it
to myself, thinking that if I could get it successfully, it would work.
Give me a second here and I'll try, but do listen to them later, because
they're .... Okay, I think I might actually be able to do this. Okay,
let me get my volume up. Well here goes, this will probably just sound
like static on the phone. Okay, that was it.

Trina That was successful.

M That was great.

W That was fantastic.

Marsha Could you get that?

Trina Yes, that was awesome.

Marsha Okay, good. Alright, so, that's about all I have to say. Are
there any questions?

M Is that change in pitch in the audio file due to the approaching and
then receding from the proximity to Enceladus?

Marsha It's the Doppler shifting of the wave, yes.

M I have a question. I remember as we were approaching Saturn, there was
a sudden increase in the E Ring; I think it was oxygen in the E Ring.
The production of ions that you mentioned here, this 125 kilograms per
second, is that sufficient to fuel that kind of increase? Is there any
link with the E Ring?

Marsha I don't think that that's sufficient. You're talking about like
the UVIS detection of huge amounts of oxygen in the magnetosphere. I'm
sure that that's not a sufficient number to sustain that.

M Okay. Thank you.

Marsha Sure. Anything else?

Hank Yes, this is Hank in Lenexa, I have a question. You mentioned, I
don't have a line, a room here, so I don't have that view graph, but on
the third view graph ... oscillations of magnetic .... Now is that the
magnetic field around Enceladus and is that random or is that periodic
at any time?

Marsha You're kind of breaking up, but I think what you asked was, are
they due to the magnetic field of Enceladus or of Saturn\'s magnetic
field? Really, we haven't with absolute certainty, detected a magnetic
field at Enceladus, so all of these magnetic field measurements are
primarily due to Saturn\'s field. Again, there is some source of water
product ions somewhere, presumably Enceladus, presumably the E Ring and
other sources, perhaps. So they're systematic and we have to determine,
what we plan to determine is where they come from. Did that kind of
answer your question?

Hank Are the oscillations, as I understand, you just said that they're
periodic?

Marsha Yes.

Hank I see.

Marsha Yes, they have a characteristic frequency and that tells you
something about the ion species that's present and producing those
waves.

Hank Do you have any idea of what causes it to be periodic?

Marsha Yes. Basically they're caused by ions kind of spiraling around
the magnetic field and the frequency, with which they do that, is
related to the charge and the mass of the particles. So for particles of
one charged to mass ratio, you'd have one frequency of waves and
particles with a different charge to mass ratio would have a different
frequency. So it's kind of an identifier of what ion species you have.

Hank I see.

Trina Marsha, we know that you have to get to another meeting, and so if
you could stop by maybe after that meeting was over, and if there were
any more questions, maybe you could call back in and we could pick up
them after the imaging presentation, would that be alright?

Marsha Sure. That's great.

Trina Okay.

Marsha Thanks, Trina.

Trina Thank you, we appreciate it.

Marsha Sure.

Trina She has to go to another sequencing meeting to defend yet another
observation that's going to be very exciting, coming up in the
near-term. I'd like to turn it over now to Dr. Elizabeth Turtle, from
the University of Arizona, about the imaging results of Enceladus, which
are beyond fascinating.

Elizabeth Thanks, Trina. I'm going to start off, actually, with a little
bit of background about Enceladus. Some of this may be a little
redundant, so I may go through it a little more quickly, since we've
already had the mag presentation.

I did want to point out that there's a long list of people on the first
slide in the presentation that I put together, and that's not by any
means a complete list of the people, that have contributed to getting
these observations and analyzing these observations and putting them all
together. There are a lot of people involved in this effort, and I just
happen to be the one who gets the fun of presenting it today.

Enceladus is a pretty small satellite; on the second slide I've got a
list of some of its physical characteristics. It was actually discovered
in 1789 in a ring plane crossing. It's so small that even though it's
quite bright, it can really only be seen when the rings are kind of
edge-on, as seen from the earth, so that you can detect the small
satellites, close in. It's significantly closer to Saturn than our moon
is to us, and as is, as I said, quite small. The radius is about 250
kilometers. Given the mass that has been measured, it has, actually, a
relatively high density for an icy satellite, which might help us
understand why its surface is so strange, especially for such a small
body.

It also has a very bright surface, the geometric albedo is about one,
it's really the brightest object in the solar system, so most of the
light, all of the light that incident upon it, is reflected back,
basically, which also means that it is very cold. Its surface
composition is almost entirely water, although there may be some
contaminates and that's something that the ISS and VIMS, especially will
be investigating.

The next slide shows --- kind of puts Enceladus in the context of the
Saturnian System, Enceladus is the second medium-sized satellite outward
from Saturn. The top slide has all the different satellites, the major
satellites of Saturn, to scale and the bottom part of the slide has them
in their locations, to scale. So you can see that Enceladus is actually
in the center of the E Ring and that's one of the things that Cassini is
designed to investigate, the relationship between Enceladus and the E
Ring. You can see, also from the top, that it's really much smaller than
the other icy satellites.

The fourth slide just puts Enceladus, again, in the context of all of
the outer planet satellites, as well as our moon, which is not an outer
planet satellite. But just for scale you can see that the Galilean
satellites of Jupiter are much larger, comparable to the size of the
moon and Titan, and then there's this other class smaller ..., and
Enceladus is one of the smaller ones of that class.

Yet, on the fifth slide, as the fifth slide shows, when Voyager flew by
the Saturnian System, it showed that despite its small size, Enceladus
actually appears to have had a significant amount of geologic history in
its past. You can see impact craters on the surface in these Voyager
views, but you can also see regions that have been distorted and
deformed and fractured by some sort of endogenic geologic process. Even
the impact craters are not pristine, they too have been deformed.

So Cassini's objectives at Enceladus are to determine, to better
determine its characteristics and to try to piece together its geologic
history, to understand not only what has happened and when, but how
recently, as well. Whether or not this activity can continue to the
present or has continued to present, as Marsha mentioned, there's some
intriguing observations in an atmosphere, the association with the E
Ring suggestions that perhaps there is some sort of distribution of
material from Enceladus, to the Saturnian System around it, and we still
don't understand that. So that's one of the major goals.

Also, to define the different processes that acted to shape the surface
of Enceladus, to investigate, as I mentioned, the composition and
distribution of materials on the surface, as well as its bulk
composition and internal structure, which is really important to
understanding the overall history of the body, whether there still is or
has been a liquid layer inside, for example. How much of its interior is
silicate and whether there's enough radiogenic heating from that to
explain how such a small body can have been active through such a long
history of the Saturnian System. Finally, one of the other major goals
is to investigate the interaction of Enceladus with Saturn\'s
magnetosphere and its ring system.

So there are several Cassini encounters with Enceladus, ranging from as
little as 175 this summer, that's been updated more recently than this
slide has been. Even perhaps, closer in a few years, out to much more
distant encounters, as well, but even the distant ones give us good
coverage of the surface and enable us to build up a global view of
Enceladus. Obviously when you flyby very closely, you only see a small
portion of the surface, so you need a combination of both, and the
mission has quite a lot of opportunities to observe Enceladus.

The eighth slide shows the coverage that Cassini had, that the imaging
experiment had of Enceladus during the 17^th^ of February flyby. The
different colored outlines just show the areas that we saw at different
resolutions, a couple of very high resolution footprints right in the
center. This is put on the Voyager-based map.

The ninth slide shows the coverage that we had in March, and you can
actually see, if you go back and forth, you can see that the region
under the area we covered in the February flyby has been filled in, so
the maps are being updated as we get more and more data. Again, you can
see some very small little footprints, very high resolution footprints
right in the middle there, of what in the Voyager data was essentially
terra incognita at this kind of scale.

So the image on the tenth slide is actually a false color view of
Enceladus. This was taken as Cassini approach Enceladus in February.
Enceladus, as I said, has a very high albedo, it's basically white. But
if you stretch it, if you stretch the images taken in different filters,
enough, you can actually bring out a bit of color. So one of the things
that this is revealing is some bluish tones in regions that look like
they've been fractured or deformed and then land or grayish areas in the
kind of plains in between them and I have a few more color ones later
on, at high resolution.

Zooming in a little bit on this observation, if you stay on slide ten,
you can see this kind of feature toward the right hand side of the disk
that makes a right angle. I can't explain that, but it's a useful, it's
just a useful landmark when you go to slide 11; that's just up at the
very top right. This is a higher resolution view, about 300 meters per
pixel of Enceladus that was actually acquired in March.

You can see the surface is --- as we get closer and closer, we see more
and more fractures on the surface. You can see there are a number of
impact craters in this region, but many of them are cut by the
fractures, so they are older than the fractures. Piecing together this
history is going to take a lot of mapping, to go in and look at all of
the images and mosaics we can make of Enceladus now and look at the
crosscutting relationships. It's convenient to have so many crosscutting
relationships, because it will help put the history of the planet
together, but it's going to take a lot of time. There are so many
different fractures and folds, as you can see, in this image and the
subsequent ones.

The 12^th^ slide is actually another very stretched color view of
Enceladus, again, taken in March and this is even closer. Again, the
blue areas, the more fractured areas seem to have a bluer cast to them,
then the plains in between.

This may be a compositional effect, but it could also just be a grain
size effect that the ice perhaps that's being revealed in these
fractures is fresher, hasn't been exposed to the environment, within the
E Ring, within the Saturnian System, as long. So the grain size may be
exposed, the solid ice there may have a higher grain size, and then
there's perhaps a smaller grain size in the regulus that's formed on the
surface. Just for scale, that big crater near the bottom of the image,
that the center is up-domed in, is about 20 kilometers in diameter.

So the 13^th^ slide has something that I'm really fascinated by. This is
an image that shows the limb of Enceladus, this was taken in February,
at about same resolution as the previous image, but it shows a variety
of morphologies of the impact craters and that's what the little letters
are pointing out. A seems to be a relatively fresh crater on its right
hand side, but on the left hand side it's been modified by these
fractures that seem to cut across it.

Then there are other areas, for example the crater near the letter "B",
which has a rim, but essentially no other topography, which is
consistent with it having viscously relaxed. Given enough time, ice can
actually flow and deform, as a solid, and being warmer helps, but it
still doesn't need to actually be a liquid to do this. As a solid, it
can do that.

But the time scale is dependent on the viscosity and that's very
temperature dependent. So being able to look at craters like this,
examples that are pristine, next to examples that have actually
undergone the viscous relaxation process, can help us constrain the
properties of the subsurface, how warm it needs to have been, for
example, to allow this to have happened in a reasonable time scale.

Then you can see the trailers labeled "C" and "D" are actually fairly
square, which is very intriguing. That could be an effect of the impact
process itself. If the tectonic fabric, if there are enough fractures
within the ice, into which the impacts occurred, those can control the
shape of an impact, it could also the shape of a final crater. But it
could also be deformation post impact. As an example, Meteor Crater,
which is significantly smaller, is actually a fairly square crater and
that was controlled, just because of the jointing fabric in the target,
but as I said, this could also be post impact deformation. So those of
us who study impact craters, certainly have our work cutout for us.

The next slide just shows another near limb view of some of these impact
craters that have central uplifts, which may be an effect of viscous
relaxation. You can also see that these are quite fractured. The craters
there, there seem to be fractures running across them.

Then 15^th^ slide, again, shows lots of impact craters. You can tell
where my interests lie. But one of the things that's intriguing about
this, these are smaller craters, and they're the more simple bowl shaped
craters, they don't have central uplifts. But they also seem to be
fairly soft and we see this in a number of places. You'll notice this
through the subsequent slides, as well.

A lot of the small craters appear to have a very ... texture, as if
there's some sort of process, perhaps just in the regulus that is
degrading the sharpness of the rims over time. But this comes, in this
image, the fractures too, have a relatively softened look, but in other
places, even though the craters have these kind of muted topography, the
fractures are quite sharp and so that also --- that, along with the
crosscutting relationship, helps us understand what the most recent, the
youngest features on the surface are. It's very intriguing that we don't
see a lot of fresh craters, even at these very small sizes.

The next slide shows a limb view of Enceladus and a variety of different
deformation types. There's a big fracture band that runs across it
that's about five kilometers wide, and you can branching, not branching
off, well in some places they do branch off or they just parallel that
crack, there are lots of smaller fractures. Then near the top there's
this, what looks more like ski trails than anything else, really, these
kind of folded, or perhaps these are older fractures that have a more
muted cast to them, the same way that some of the craters do. One of the
things you notice in this area is that there aren't a lot of impact
craters. There are a variety of surface ages exposed on Enceladus.

The next set of slides just go through some of the fractures in more
detail. The 17^th^ one shows a fracture cutting across older fractures
and you can see that the edge of that kind of fracture that runs from
the upper left to the lower right, is fairly sharp and you see the
shadows cast by that. We can use those to calculate heights and in
general the depths of these fractures seem to be a few hundred meters,
maybe 500 meters in places. So again, just looking at this image, you
can see that it's going to take a long time to really map out all the
relationships between these fractures, to really understand the history.

The next slide shows a broader area that was imaged in March, at a
variety of resolutions. The little frame at the far left, that's canted
at an angle to the rest of them, is about 30 kilometers across, just for
scale. You can see, again, a variety of scales of fractures, some very
fine fractures, they get down to about 100 meters across; and again,
they're cutting the craters in a very intriguing way. It almost looks
like they're focused into the centers of some of these craters. That's
something that could just be a result of the change --- the fact that
the impact crater has changed the structure of the crust in that region.
So the fracturing was affected by the change, due to the impact feature
there.

This is something that we'll be looking into, to try to understand the
stress regime of Enceladus' lithosphere. Then you don't see small
craters, there don't seem to be many small craters that are younger than
the fractures, most of the craters are cut by fractures rather than
having impacted into them.

The next slide is another color view, and this is one of the best
examples that show the bright blue areas seem to be exposed in the
scarps, the freshest scarps and then at the base of them there's just
more gray material. So again, this suggests that what's being exposed is
a fresher, perhaps, more competent, larger grain sized material. The
large fracture across the bottom of this frame is about 85 kilometers
long and it's about 500 meters deep.

The next slide shows, again, a complex relationship between craters and
fractures. The craters in this slide, I'm on slide 20 now, look very,
very muted and the fractures are significantly younger. In fact, about
halfway across the image there's a north/south or an up/down fracture,
that's actually a bit of a scarp and then it drops off to a lower area
on the left hand side of the image.

If you're familiar with Cyclops Web site, if you go to --- it's at
cyclops.org and look under the imaging diary, or the images of Enceladus
that were taken in March, there's actually a stereo view of this that's
available. I didn't put it in the presentation; I wasn't sure how many
people would actually have red/blue glasses at hand. But you can
actually see a stereo version of this, that shows that drop off, it's
really quite dramatic. You can also see that the region on the right has
more craters, even though they're kind of subtle and degraded than the
region on the left.

Trina Betty, is this an example of where the craters on the left look
younger than the fractures, those two little ones and maybe even the one
that cuts that big trench, up and down?

Elizabeth Well the one right in the center of the image, is very hard to
tell which is younger there, actually, whether it's younger than the
fracture or not. It's something that has been bothering me, actually. It
may well be younger than the fracture, but the fact that the fracture is
preserved running up the rim of that crater, you can see the edge of
that fracture is preserved, most of the way up the rim of the crater,
and yet the rim of the crater isn't sharp, it's very soft. So I don't
fully understand how this has evolved.

Trina Yes, that's tricky. What about the two little ones, like on the
left, the one that's middle left and sort of bottom left, those both
look like they're on top of the fractures.

Elizabeth Yes, those are on top of those fractures, yes.

Trina Oh, okay.

Elizabeth Yes. So there are cases where there are craters that are
younger than the fractures. But there aren't many, which indicates that
the endogenic geologic activity has occurred much more recently,
overall.

The next slide is one of the highest resolution images that we have.
Again, you can make out these circular depressions that are these muted
craters, and there are a few, very small fresh ones. This is a 30 meter,
per pixel image. But the fractures are much younger, and you can see,
right at the top for example, you can see this very jagged profile,
which is casting shadows, which is just spectacular. You can see the
same down toward the bottom left.

So there's something --- the fact that these fractures, first of all
they're quite fresh, in that the topography is still quite sharp. This
also shows that there must be something fairly coherent, fairly strong,
near the surface that is able to maintain topography, even though we see
that the craters are fairly muted. So it's a very interesting
comparison, to see such sharp fractures standing up and then these very
degraded craters.

The 22^nd^ slide compares some views of Ganymede, Europa and Enceladus,
and these are very roughly to the same scale. So the view of Enceladus,
the view of Enceladus that's in the upper right, is the same view that
was in the previous slide, but it's been rotated so that the sun angle,
the sun is now illuminating that surface from below, from the bottom of
the picture and that's the same as the little picture of Europa beneath
it, the sun in that is also coming from below.

The Cassini image is about 30 kilometers across. And as I said, I tried
to make sure these are all pretty close to the same, but they're not
exact. But you can see that it's a very different surface from --- the
Enceladus surface is very different from that of Ganymede and Europa, at
comparable scales. Ganymede also has a lot of fracturing and faulting.
Europe actually has a lot of this compressional ridge or, well it's not
100% understood what forms the ridges. But it has a lot more ridges;
there are also fractures that cut the surface of Europa, of course, but
many of those seem to develop these ridges, whereas Enceladus just seems
to have fractures, for the most part, not entirely, which I'll be
getting to.

The next slide shows another very intriguing feature, associated with a
fracture belt. This area, you can see running right down the center of
the image, there's a region that's kind of folded or fractured and
there's some very dark spots in that. At first we wondered if this might
actually be a compositional difference. But the VIMS instrument, which
also observed it this time, although they can't quite resolve all of
those little spots individually, they do have data that covers this part
of the surface, and they don't see any evidence that those are different
compositionally.

So one of the working hypotheses is that those are actually pits, just
little pits that have opened up in the ice surface, the regulus,
perhaps, over this region where there are fractures. That would be
consistent with the fact that they seem to be correlated with the
existence of fractures. We do see these little dark spots, elsewhere.
They're about a hundred meters across; some of them are up to several
hundred meters across.

M The lighting appears to be coming from below, is it possible that
those are shadows?

Elizabeth Well if they're pits, there would be shadows. It doesn't look
like in --- there isn't a bright spot right beneath each of the dark
spots. So if they were boulders, for example on the surface casting
shadows, then you would expect to see something bright, below the dark
spot and we don't see that. It would be inverse of some of the craters
you can see on the left, where it first has a dip and so there's a dark
area and then the crater lip comes back up and it's illuminated and it's
bright.

So if they were boulders, we'd expect an inverted pattern, with a bright
bottom and a dark top, and since we don't see that, it suggests that if
they are shadows, they're not being cast by topographic features. But if
they were just pits, if there was just a fairly flat surface and cracks
had formed beneath the regulus and there pits and material falling down
into it, then you might expect that you'd just get these dark spots.

The next slide shows a close view of one of those fractures that I
showed earlier. Again, you can see shadows in the margin, but you can
also see areas where there appear to be these little dark spots that may
be either shadows in pits, in some places you can see little bright
spots beneath them and that would be a case where there's a little bit
of topographic relief casting a shadow.

So I mentioned that we see a lot of fractures, and we don't see a lot of
ridges, the way we do on Europa, but we do see some ridges, we do some
topographic features, some positive topographic relief, and the next
slide is one I showed earlier, but this shows the ridges on the left.
You can see there's that same fracture belt crossing the middle of the
image, but then off to its left, there's this region with all these
positive topographic ridges.

The next slide just shows that region zoomed in a bit, a higher
resolution image, and the sun again, is coming from the bottom here, and
based on the shadows, those ridges are about a kilometer high. So there
has been some sort of compressional deformation of the surface, as well.

In some places, they look kind of complex, right below the label 1.4
kilometers, you can see that there's kind of a --- it looks like a
trough along the top of it. But these ridges are very different from the
ones on Europa. They don't have the same double ridge morphology really,
that we see on Europa.

There are also some areas, the next slide shows an example of an area
with just some topographic domes, in areas that have been uplifted. Then
another example of the topography is this limb view that we caught, in
February, as we approached quite close to Enceladus, and you can see
some of the crater rims on the surface. Actually at the far left there's
a little bright area that's casting a bit of a shadow, it looks like a
little cone sitting up on the surface. So the origins of this positive
topography, the ridges seem to be, fairly, clearly, compressional
deformations, but these isolated domes and this cone feature and a
couple other features are still something we're working to understand.

Then just beneath that region I showed with the ridges, you can see this
area in the 29^th^ slide that has some clear evidence of shearing of the
surface. There's this folding, this kind of vertical folding that we're
looking down, not vertical folding, but it looks vertical in here, we're
looking down on the folding deformation of the surface. So it looks like
in these areas, some of the surface, there's been some motion of one
part of the surface relative to the other, similar to strikes that do
faulting on Earth, except that we're not actually getting faulting in
these regions, we're getting this folding and shearing.

There are a few places where we see little strike/slip type offsets. But
not much at all, it's not nearly at the level that we see all the
strikes that are faulting on Europa.

The 30^th^ slide also shows an area where it looks like there's been
kind of deformation folding of the surface, which speaks to the
properties of the surface, when the stress that caused this was applied.
If the stress was applied very quickly or in a very cold medium, very
cold ice, you might expect it to just fracture. But if the ice is warmer
or the stress is applied over a long period of time, then you can get
this folding instead. So we'll be able to use the observed deformation
to try to understand the near surface properties of Enceladus with this
theorem.

Then the last slide I put in just shows a view of Enceladus that Cassini
acquired as it was backing away from Enceladus, after the last close
flyby and I just put a summary of what we've seen. Most of the
observations of Enceladus are still being analyzed. There's more we
don't understand than what we do understand. But we are seeing older
crater terrains and in those terrains there's a variety of crater
morphologies, many craters have been modified by viscous relaxation,
many have been overprinted by fracturing. Even on the smaller scale, the
craters appear smoothed.

We've seen fractures everywhere. There are multiple sets and
orientations and they're relatively fresh and they extend at basically
any resolution. No matter how close you get to Enceladus, you keep
seeing fractures at smaller and smaller scales. And they're exposing
color differences, which will hopefully help us to understand the
material properties of the near surface.

We're also seeing these topographic features I showed, the ridges and
the domes. And sheared surface features, so there's clearly been quite a
tortured history to the surface of Enceladus. There has obviously been a
lot of endogenic activity in the past. There's no evidence that anything
is ongoing today, but we can't disprove it either. We just haven't been
able to find any evidence yet, and that's one of the major targets of
observations that will be coming up in the future. So I'll end there,
and if there are questions, I can speak to them.

Jane I have a question, this is Jane in Cassini Outreach. What about ice
volcanoes and geysers?

Elizabeth We haven't seen any evidence for that. There are a few little
features, as I pointed out, there's some of these topographic features,
they could be the result of --- there are some places where we've
wondered, we've looked at the little topographic feature and wondered,
oh could that be something that was actually formed by some sort of
extrusive activity. But we haven't seen any conclusive evidence for
plumes along the limb. We've had observations designed at high phase
angle, to look for plumes along the limb and we haven't seen anything
that is demonstratively extrusive activity, plume activity. So it's
something that we're continuing to look for.

We also haven't seen any strong evidence of flows or things like on the
surface. But clearly, one of the best ways to explain the fact that the
surface can have undergone such, so much deformation, so much fracturing
and shearing, is that there's been a warm, perhaps liquid interior, and
if that's the case, then depending on the energetics, you might be able
to get that extruded at some point in Enceladus' past, if not presently.

Jane Thank you.

Loretta Zibby, this is Loretta at \.... How are you doing? I had a
question, what would be some of the sources for the stresses on the
surface? I mean it's not that close to Saturn, is it gravitational
stress, do you think, or what?

Elizabeth Well that's a very good question and one of the things that we
need to do, to understand what the stresses are, is to map out all the
different features, the compressional and the extensional features, and
see if there are any patterns that develop. There shouldn't be a lot of
tidal deformation that occur in epoch, but that may have been different
in the past.

One of the major sources for stress, especially for the extensional
features, could simply be cooling. As ice freezes, of course, it
expands. So you could actually get these kinds of sets of fractures that
we see, simply by cooling.

Loretta What would cause the temperature differences? I mean why would
it need to cool, why would it have been warmed?

Elizabeth Well when it formed it would have been warm.

Loretta Oh, when it formed, okay.

Elizabeth Yes, when it formed and if it went through some sort of tidal
resonance, during its history, then it might have been warmed up by
something like that. But I can't say that that actually has happened. It
could be that it's just heat left over from its formation and from the
decay of the radioactive elements within the silicate part of the
planet.

Loretta Okay. Thanks.

Elizabeth Sure.

M Can you estimate the ages..., like within the last couple of hundred
million years or one million years, what would you guess?

Elizabeth There's a group in Germany that is actively doing crater
counts, to constrain the ages of the surface. The ages of the areas that
have a lot of craters, are comparable to the ages of the other
satellites in the Saturnian System. So they're quite old, billions of
years. But I don't think we can yet put an age on the younger looking
parts of the surface.

M You wouldn't even guess within the last, let's say, hundred million
years.

Elizabeth I'm not going to guess, no. I mean there are so many different
processes that are degrading the craters. There's the endogenic crater
relaxation processes, there's fracturing and folding that will also
tectonically resurface the planet. But then there's also this kind of
degradation that's just smoothing, and that may just be a regulus
process. So those will act, perhaps on different time scales and it's
just too much history to unravel. So I'm not willing to guess, yet.

M The magnetometer data should give you a much better idea, wouldn't you
think?

Elizabeth In what way?

M If it indicates that there is a subsurface ocean, right now.

Elizabeth Right, yes it could indicate that there's a liquid interior
and that would be quite consistent with what we're seeing. But that
doesn't require that there be ongoing tectonic deformation today. But it
would be a good piece of evidence that it might continue to be ongoing.

M Great, I thought that was why they wanted to get closer, actually.

Elizabeth Yes, that's exactly why we want to get closer.

Pete Hello, this is Pete Goldie, in San Francisco. I see that the
density is above one, so there must be a rocky core at some point.

Elizabeth Yes.

Pete With that rocky core, can you hazard a guess as to how deep the ice
coating would be on that?

Elizabeth I don't have those numbers on the tip of my tongue, I'm
afraid. One can calculate it, the diameter of the core based on the
density, and the fact that we know that the top is water ice, if you
just assume that the interior is silicate, but I don't have those
numbers, I couldn't give you that right now.

I mean this is relatively high compared to some of the other icy
Saturnian satellites and that may help explain why they've been more
endogenically active then some of the others, if it had more silicate
material, if it incorporated more silicate material and therefore had a
higher amount of the radiogenic materials.

Pete Would you presume that the relaxation of crater walls, in such
material, is more likely to have caused endogenic by endogenic processes
than exogenic?

Elizabeth Yes, well crater relaxation is something that will just occur,
but as I said, depending on the time scale and effect viscosity of the
material, but it's not something that's strongly affected by exterior
processes, it's just the natural process of the ice, the fact that you
get this crater that is not in gravitational equilibrium, it will slowly
just relax back. The same thing happens, if you scoop out some honey,
it's much less viscous, but if you scoop a spoonful of honey, the hole
that you leave will collapse and it's the same thing happening on the
icy satellites, just on a much longer time scale.

The only way you could get the exogenic --- the only way you could
really tie that to an exogenic process, would be if there was some
really large impact that it actually heated the area around it, but that
would probably overprint the crater anyway.

Pete And say high energy ionic bombardment would be insufficient to
soften those craters.

Elizabeth Yes, I mean the deformation that's occurring, the craters that
are relaxing are 20 kilometers across and they're a few kilometers deep
and the region of the crust that is actually deforming, as the crater
relaxes, is a few or several kilometers beneath the surface. So the very
surficial effects wouldn't help in that respect.

Pete Thank you.

Loretta Zibby, I have another question, this is Loretta again. On the E
Ring, that Enceladus is sharing around Saturn. Is it traveling through
the particles or are they all in orbit and it's not traveling through
the particles or can you tell?

Elizabeth Well it would be moving with the particles there. But they'll
have, probably, slightly different velocities, so they probably are
impacting it to some extent and maybe also being released from
Enceladus. So that may play a role in the regulus, the particles in the
E Ring may well be playing a role in the regulus development on the
surface.

Loretta Could they be degrading the craters?

Elizabeth They could be. I'm not sure how deeply those will affect the
regulus, but given enough time, the regulus continues to get deeper and
deeper, and so I don't know if the micrometeorite impacts are sufficient
to do that or not. But that's certainly something that I'm suspicious
of.

Loretta So none of the other moons are in a ring like that, except for
the separate rings around the F Ring, right?

Elizabeth Actually if you go back to the third slide, you can see that
Enceladus is in the --- it's a schematic, but this is in the kind of
densest part of the E Ring and that's why there's this question as to
what it's relationship is and whether it could actually be providing
material for the E Ring. But many of the other little satellites here,
Mimas, Tethys, Dione, Rhea, they're all within the kind of distributed
area of higher density particles. So there may be affects on them, as
well, from that environment.

Loretta Oh, okay.

Tom This is Tom Ross from Lavonia. I was wondering if you could tell me
what would be the best ongoing Web site to monitor the outcomes of the
different data?

Elizabeth Well I'm rather biased to the imaging Web site, obviously
that's the cyclops.org site that I mentioned. Of course the JPL Web site
has all of the images, as well as data from the other instruments, and
the Planetary Society has quite a good summary, as well. Those are the
ones that I tend to look at.

Tom Okay, thank you.

Bob Bob Polson, South Dakota. Is there any evidence of anything other
than water ice on the surface of Enceladus?

Elizabeth At this point I don't think anything has been definitively
identified. VIMS is a better instrument for detecting compositional
variations and I'm afraid I can't speak to the most recent data.

Bob Okay. We know or don't know whether there's any atmosphere around
this moon?

Elizabeth The magnetospheric data that Marsha spoke about, and maybe
she's back on line and can answer this better than me, but those data
suggest that there is an atmosphere, a very tenuous atmosphere around
Enceladus. An atmosphere hasn't been detected by any of the other
instruments, yet. But what that may do is put an upper and lower limit,
the magnetic data can put a lower limit on the number of particles
around Enceladus and UVIS and ISS and perhaps INMS can put an upper
limit, and so we may be able to use the different observations to
constrain it.

Bob So if there is an atmosphere and it's been there for a long enough
time, we could also be seeing some evidence of wind erosion.

Elizabeth The atmosphere is too tenuous at this point for there to be
any sort of effects of it, directly on the surface. It's basically an
atmosphere, like the atmosphere of our moon, it's atoms that are
somewhat gravitationally bound, but as I said, Enceladus is quite small,
so it's very easy for atoms to escape. So it's not an atmosphere, in the
way we tend to think of an atmosphere, as we on Earth or say at Titan,
it's just a slightly higher density region of gasses around the planet.

Trina So Zibby is there any big area of Enceladus yet, that we have not
seen, that you're sort of looking forward to seeing in one of these
flybys that's coming?

Elizabeth If you look at the maps ....

Trina It looks like maybe right around 90 degrees or so.

Elizabeth Yes, there's an area kind of around 90, 45 degrees that we
haven't seen very well, and we haven't seen the poles very well, either.
I think we'll have better coverage of those in some of the upcoming
flybys. I think the one this summer, that's just moved closer, is a
pretty good view of one of the poles.

Trina So if you had to pick, would you say Enceladus is your favorite,
or? It's a tough choice.

Elizabeth It's a very tough choice. Usually my favorite satellite seems
to be the one that we've gotten the most recent data from, and Enceladus
is certainly a really intriguing place. I think at this point, I'm
actually more intrigued by Iapetus. And of course there's Titan, which
is incredibly mysterious and we don't understand it all, which makes it
very exciting.

Chuck This is Chuck Marvel, in California, unfortunately I missed some
of the teleconference, for another business issue, I'm sorry about that.
Have you covered anything about the latent electra of the latent
magnetic field on Enceladus and what they might have to imply as far a
liquid or semi-liquid mantle?

Elizabeth Is Marsha back on?

Trina Yes, Chuck, we actually did do that, we did that first. There's a
presentation from the magnetometer team, if you download that. We've got
ten pages or so on the magnetic field observations.

Chuck Fantastic, I'll review that. I'm sorry I missed the early part of
the call; this has been fascinating, good job, guys.

Trina No problem, we'll be uploading the audio file later this week and
you can download it and relisten.

Chuck Thank you. I'm very curious to see that. That should tell us a lot
about what's going on down there. Thank you.

Elizabeth The other thing, I'm not sure if this is in the presentation,
I guess it is in the presentation, but the tour has been tweaked to move
the July flyby of Enceladus, I think closer, significantly closer, I
think Marsha said 175 kilometers altitude from Enceladus, that will give
us an even better data point on the magnetic field issue.

Chuck Thank you very much.

Steve This is Steve Lee, in Denver, talking about tweaking the future
approaches, if you saw something really intriguing, is there any
flexibility to dramatically change the sub spacecraft point at closest
approach, is that more or less dictated purely by celestial mechanics at
this point?

Elizabeth It's mostly dictated by celestial mechanics, I think it would
depend on just how intriguing the observation was. It's harder to change
the sub spacecraft point, than it is to change, for example in the
Enceladus flyby, we moved much closer, but we're still flying over a
very similar part of Enceladus.

Steve Okay. Thanks.

Elizabeth But the tour has been changed a number of times already to
move closer to or further from various satellites, in reaction to either
interesting observations, such as the magnetospheric detection at
Enceladus, the atmospheric detection or a hazard, as well. So the tour
has been tweaked a number of times and it's actually quite nice to see
that it's going to be able to be this flexible.

Steve Alright, thank you.

Trina Now that's actually sort of the definition, I don't know if it's
an official definition, but at least on the project, the definition of
the tweak is that you're not changing the sub spacecraft point or
anything like that, you're just changing the altitude. If you actually
changed the flyby significantly swapped one moon in for another or
changed the sub spacecraft point, we'd call that tour redesign.

Steve Okay.

Trina Yes, and we don't have the workforce for that. I'm already dying
in just the tweaks. I don't know about anybody else.

Elizabeth Yes, the tweaks are plenty.

Trina Are there any more questions?

M Yes, I've got a question, about the ridges. On your slide with
comparing Ganymede, Enceladus and Europa, are the ridges similar height
compared to the diameter on all these satellites or how do they compare?

Elizabeth Compared to the diameter, no. Compared to the diameter,
actually, Enceladus is much flatter than other Saturnian satellites; I
guess it's not flatter to Europa, compared to its radius. But Europa is
a lot bigger.

M Right, so if it's flatter, that would indicate a lot more movement, I
guess. Is that right?

Elizabeth Yes. I mean Iapetus has substantially more topography than
Enceladus, which is really the opposite of what you'd expect, since
Iapetus is bigger. So it does imply that the lithosphere of Enceladus is
not capable of supporting significant topography and therefore must be
rather more mobile.

M Could that be a stronger indication for a subsurface ocean or internal
tectonics?

Elizabeth It would be consistent with a fairly warm interior, yes. It
probably doesn't have to be a liquid, just to reduce the topography, as
we've seen. But to a certain extent that will depend on the timescale
and we don't have a good handle on that yet, because we're still
analyzing the data.

M Is there any conceivable way in which you would imagine some of the
surface soft or liquid and the remainder of the surface very cold and
rigid?

Elizabeth I think there's actually a fair amount of evidence that some
areas of the surface have been warmer than others in the past, simply by
looking at some of the areas where we can see craters, and in some
places the craters are fairly deformed and relaxed and in other places
nearby they're not, and that may be an indication that the lithosphere
was warmer in one place than another. We don't see evidence that I think
is conclusive for any flows on the surface or actually evidence of
liquid on the surface.

M I've got a question. The radiation environment, how does it compare
and how does it compare to Jupiter?

Elizabeth In general --- I'm really not terribly well qualified to
answer questions about radiation environments, but in general the
radiation environment is much, much lower here than at Jupiter. The
environment near Europa is much higher, there's a lot more radiation
there, just because Jupiter has a huge magnetic field, comparatively,
and the satellites are closer, I believe.

M Thank you. What about ammonia?

Elizabeth Ammonia is a leading candidate for trying to explain how one
can maintain a warm interior, a liquid interior or at least a low
viscosity interior throughout much of the history of the icy Saturnian
satellites, in general, not just Enceladus, but others that have
evidence for tectonic activity.

The problem is that ammonia is quite easily broken down by UV radiation.
So for example on Enceladus' surface, which is exposed to all the UV
radiation coming in from the sun, the ammonia isn't likely to be able to
last very long. But it may well be present in the interior, and it's
just that it's been destroyed in the very near surface, and so that's
something that people are looking very hard for, because it makes it a
lot easier to explain how we can have had so much activity.

M You would be able to detect it at some time, if it was there, with the
instruments onboard?

Elizabeth The instruments onboard would be able to detect it, if there
was enough there. The question is whether it can survive on the surface,
to be detected.

M Let me ask one other question; that bulge on Iapetus, to change the
subject for a moment, any speculation?

Elizabeth No. It's wild, it's absolutely wild. It's hard right now to
try to assess formation theories, if it goes all the way around Iapetus
or not. There's some tantalizing hints from Voyager images that there's
topography along the equator on the other side, but we won't really know
for a few years, whether it goes all the way around, but people are
looking into ideas such as despinning, reducing the rotation rate, for
example, which causes stress in the lithosphere, can cause the formation
of such a feature. Most of the models for that, however, predict a lot
of tectonic features elsewhere, a lot of fracturing and faulting
elsewhere on the satellite, we just see that ridge along the center. So
it's still a big mystery.

M It's what, at least halfway round, right, or three-quarters?

Elizabeth It goes at least halfway around, yes. See that's the other
reason that it's hard to speculate on its formation, is because right
now we've really only seen the dark side of Iapetus, and that's the side
that we're seeing this ridge on. We don't know if it's just in the dark
region, then maybe it's related to the dark region, specifically. But if
it goes all the way around, then it's probably not related to just the
formation of the dark region. So we have to be patient and wait for some
more data. But people are already modeling various formation theories,
without being patient.

Trina Well that's a good idea, keep the theorists busy for awhile.

Elizabeth That's right.

Trina Any more questions? Okay, well I'd like to thank Marsha Burton and
Dr. Elizabeth Turtle today, both of their presentations were fabulous
and Enceladus is certainly very, very intriguing.

Our next CHARM telecon will be on May 31^st^. We expect that the topic
of that telecon will be the radio science occultations. For those of you
who are familiar, sort of with the general layout of the Cassini tour,
we sort of spent the first six or seven months getting into orbit, doing
the Huygens release and then the very first thing, in terms of the tour
that we did, was set up a series of radio science occultations.

Those occulations begin on May 2^nd^ of this year and go through
September. They're the highest priority observations of both the rings
discipline and part of the atmosphere discipline. They're just hugely
important and they're very exciting. And so they're going to start
coming one after the other, and I'm desperately trying to get the radio
science team to come and give us a presentation on May 31^st^.

So that's it for today. Thanks everybody. Have a great week.

All Thank you.

W Thanks, Zibby.