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

**FTS-NASA VOICE**

**Moderator: Trina Ray**

**November 25, 2008**

**1:00 pm CT**

Jane Houston Jones: Okay. Welcome everybody to the November 25th CHARM
telecon. Today we have three speakers who are going to talk about
Enceladus, results of recent Cassini flybys of the active moon.

Now with us today we have Paul Helfenstein from the Imaging Team, John
Spencer from the CIRS team and Sascha Kempf from the CDA team.

Now for those of you on the phone, the PDF version which is on the
public Web site has been combined into one document. However the
PowerPoint documents, we left them in their original format because each
of our speakers had a beautiful presentation and we didn't want to lose
the - lose all of the background material by combining them.

We're going to start this particular talk with Trina Ray who's going to
give us just a few slides worth of introductory material which is also
on the PDF at the beginning. And it has a separate PowerPoint.

So with that Trina I'll take - I'll give it to you.

Trina Ray: Okay, welcome everyone to the CHARM telecom today. As Jane
said, we really do have some very exciting materials to be presented.

Enceladus has turned out to be one of the most exciting targets that
Cassini has studied even back as far as many years ago with Voyager, we
knew that Enceladus was going to be interesting. But it has just turned
out to be sort of interesting beyond our wildest expectations.

The second slide in the presentation, this is a nice view or picture of
the flybys that are coming up.

Now we had three flybys in the main mission, in Cassini's prime mission.
And it was near the first flyby that the magnetometer instrument sort of
noticed something interesting about Enceladus in particular, something
going on towards the south. It was the second flyby where we really got
some fantastic data from the CIRS instrument and the INMS instrument
where we saw the hot spot at the south and also flew through the water
cloud.

And then it was later in 2005 when we took those first very, very
spectacular images near actually Thanksgiving of 2005. So that was a -
that was really nice. And that's where we really saw the plume.

So this picture here shows the plume that's shooting out of the South
Pole of Enceladus. And it shows the trajectory of the flybys that are
happening in the 2005 flyby but then also the ones that have happened
this year and the ones that will be upcoming.

And you can see that we've got some exciting sort of, you know, diagonal
flybys where you go very close to the equator and then sort of shoot
through the plume. But you're further away from the sort of the source
of the jet when you're flying to the plume.

But then notice right there those E7 and E9 flybys that shoot right
across the middle. Those are going to happen next year. And we're
really, really looking forward to those flybys.

So this gives you sort of a nice quick overview of the trajectories of
the Cassini spacecraft near and through - near Enceladus and through the
plumes for the extended mission that we're in right now.

If we go on to the next slide, Slide Number 3, all the instruments have
just been doing fantastic stuff at Enceladus. And it really - it's one
of those things where it's sort of, you know, it takes a village. Anyone
instrument alone would - you would be challenged to understand what's
going on. But all of them together really help you put together the full
rich story that is the Enceladus that is this little moon, Enceladus.

We've got information that we'll be presenting today on its surface. And
I think perhaps Paul will be talking about composition perhaps. But also
we definitely have some thermal presentations that will be done today
and dust results that will be presented today from the scientists who
are joining us.

If we go on to the next slide which is Slide Number 4 in the package,
this shows you the upcoming flybys, the upcoming flybys in 2009 and
2010. This is what will wrap up the Cassini extended mission. You'll see
in particular those E7 and E9 that just shoot across right through the
plume, right through the jets. Those are some that are - really have
some exciting potential and really looking forward to those flybys that
are coming.

And with that that's the conclusion of the introductory material. We'll
go ahead and hand it off to Dr. Paul Helfenstein who's with us from
Cornell today.

Paul Helfenstein: Hi, can you hear me? Okay, let's see, let me get
started here. We're going to be talking right now about a little bit of
surface geology that we've been doing with the high resolution imaging.
But I think I sort of - I need to get us oriented on our area of
geologic interest.

If you go to the next slide you'll see three images, whole disk images
of Enceladus. Up until 2008, our best imaging was done from three close
flybys all in 2005.

Of those three be only one that really showed us a good view of the
South Pole where the action is was on the 11th orbit, on Rev 11. And
that was in July of 2005.

Now what's particularly interesting about this and relevant to what
we're going to talk about today is that we managed to get one image
during that time at an extraordinarily high space resolution of four
meters per pixel. And that drove a lot of the planning that's led to the
images I'm going to show you today.

In event if you go to the next slide okay, this sort of focuses a little
bit more on orienting toward our area of interest. This is a false color
mosaic of Enceladus taken with the Cassini narrow angled camera. There
are three wavelengths used here - an ultraviolet wavelength, a green
wavelength and an infrared wavelength. So it's a false color image.

And in this image, areas that are greenish are areas that represent ice
that has a fairly coarse grain size. In other words, according to
(Stefali) and (Porco) in 2006, we'd estimate the grain size in these
greenish areas as being about 100 microns or so in diameter.

The whiter areas in this representation represent finer, finer frost -
of frost particles more with diameters closer to 10 microns.

So what you can see you right away is that that tiger stripes stands
out. The tiger stripes are actually called tiger stripes because when we
first saw them at a low resolution and low angle, they actually did look
like dark stripes in contrast to the brighter material.

So at a higher resolution view, tiger stripes are about 130 kilometers
long. Their spaced about 35 kilometers apart. And they appear greenish
because as I say, for some reason coarser particles lined up with the
rest, okay.

So the area as a whole, you'll see a letters A, B and C. This is
basically a tectonic boundary that isolates the South region from the
rest of Enceladus.

This is sort of a - in comparison to the other terrains on the South
there are very few craters. It's a very young area. And we know that
geologically, volcanically and tectonically active. We don't have to -
in particular the area that -the band that isolates it from the rest of
Enceladus is a subkilometer scale scarf that actually encircles the
South Pole. The South Pole is just about dead center of where you see
the tiger stripes in. So you have this prominent arching scarf. In some
places it intersects to form these sharp cuts.

In other areas where it intersects there are icy mountain's being wedged
and pushed up in-between the cuts.

We're not going to be talking about that so much today. But this sort of
sets the stage for trying to understand the geology and the tectonic.
There's something obviously peculiar going on with the tiger stripes to
make them - make the surface materials be course grained on either side
of the fracture.

Okay, so we're going to move on to the next slide. And this is - I put
this in just to remind myself is that the tiger stripes appear to be
primarily the area from which the plumes are erupting. And this is a
high resolution view of the plumes.

And particularly if you look - you notice that the plumage isn't just a
broad diffuse cloud. They are jets and they can be seen emanating from
the surface right up to the limb.

Now our team leader (Carolyn Porco) and (Joe Stefali) worked on multiple
views of these jets and were able to actually triangulate the
intersection with the surface from, you know, basically the eruption
site, which at least eight of these jets were erupting from the surface.
And they turned out to be - coincide pretty much with the tiger stripe.

So our game plan in the close up flybys that we had in August and at the
end of October was to get the - basically the closest high resolution of
the eruption site so we could tell geologically what the - what makes
them so distinct or if there is something that makes them so distinct,
very distinct from other fractures and rifts in the South Polar area and
elsewhere.

Can we go to the next slide? Okay. Now one of the things that motivated
this was actually this very high resolution four meters per pixel image
that I mentioned earlier. We were not -when that image was taken the ISS
was not actually the prime instrument that was pointing the spacecraft.

In fact, what was happening back in 2005 was that the ultraviolet
instrument UVIS was interested in imaging a star as it passed at close
range behind - as it passed behind Enceladus when Enceladus was very
close to the spacecraft.

The idea being that as the star passes close to the limb, if there's any
atmosphere, if there was any atmosphere on Enceladus the satellite would
be attenuated according to the density of water vapor just above the
surface.

And so what we did is we road along with that. We took our camera and
we, you know, we were sort of collimated with the same pointing
direction as UVIS instrument that we started taking pictures as fast as
we could.

Now in this particular case, because Enceladus was sweeping by the
camera so fast, there was no way we could have actually targeted this -
a specific site on the surface even if we wanted to.

So we basically just started shuttering the camera over and over and
over again. And we were lucky enough to actually catch four meters - a
four meters per pixel image of a region near the tiger stripes but not
on them.

So there's a - this image now that I'm showing you is just a subset of
that color -that false color mosaic. And you see a scale there.

If you look at toward the bottom of the mosaic, you'll see a couple
rectangles \-- a small one and a larger one. Those actually represent -
we're looking at an oblique angle at the surface.

And you'll notice these rectangles actually represent the fields of view
of the narrow angled camera. That's the little rectangle, and a larger
rectangle which is the wide angle camera. The wide angle camera, we
sometimes use these two cameras in tandem.

The wide angle camera gives a sort of a larger field of view in a
context so we can fit this little tiny postage stamp and identify what's
around it.

So as you can see, these two images, the WAC and the NAC images ended
right up at the very end of a tiger stripe, not on it. It was right
where the tiger stripe sort of splits up and ends up in a highly
fractured area.

Okay, we go to the next slide and the next slide really just shows us
what these images look like. So the image at the left is the wide angle
camera. And then you'll see an area that's highly fractured at many
different scales. There are areas that appear relatively smooth, others
that appear very hummocky.

Now the little black square represents the field of view of a narrow
angle camera. And we were quite surprised when we saw this image. That
image was shown down at the lower right. And you see a scale bar there
at about 200 meters per pixel.

And so what you see is even at the small, there are for instance
orthogonal fracture sets that are all over the place. And there are
these - it's kind of very interesting, 10 meter scale and smaller
boulders or - we call them ice now.

We have to be careful when geologically you call something a boulder.
Anyway, they are large ice blocks, larger than a house and, you know,
ranging down to smaller size. In some lower areas you can actually see a
smooth deposit.

And basically this is quite of an interpretive perspective of a field
deposit. We thought it was really terrific to understand what was going
on with the tiger stripes.

If we could actually get right down to the surface as much as possible
to the point we were actually seeing individual blocks and boulders and
that this most probably would tell us a great deal about what makes
tiger stripes distinct.

If I go to the next slide, okay so and what I'm going to show you, we
basically had two opportunities to take what we call skeet shoot images.
And I'll explain that in a little bit.

But our scientific objectives, I like to observe the morphological
scales of volcanic features at better than 10 meters per pixel, you
know, and basically on the lines of high resolution pictures.

And we want to - we're going to look for special manifestations related
to their age and evolution.

But eventually these pictures become Rosetta (stones). We can't take a
lot of them. So we've got to be wise about how we use them. But they may
provide us a key for understanding other areas of the surface that we're
not able to map or to observe.

We want to see this as the Rosetta stone for understanding a wider
distribution of other examples that we report to you as slightly lower
resolutions \-- much lower resolution.

We really want to ultimately map these as terrain units, identify
systematic geological and tectonic relationships and interpret their
physical significance.

So at this point in the game we're mostly working on one. And probably
have more to say about it at the AGU conference coming up in December.

But basically what I want to do is sort of get you started on the mean
images that we've got.

Okay, so what is skeet shoot? You know, you've heard this term already
probably multiple times. Why are we using this approach?

Just want to remind you, a closest approach at least in August, our
altitude was only 50 kilometers \-- about 30 miles above the surface of
Enceladus. And Enceladus was whipping by us at about 40,000 kilometers
an hour at 24,000 miles an hour.

The imaging cameras basically along with a lot of the other optical
lenses is essentially bolted to the side of the spacecraft. And the
spacecraft is as big as a bus. You have to turn the entire spacecraft
for the camera.

Now we have two ways of turning the spacecraft. One is with reaction
wheels, the fly wheel. And the other is with little reactions, little
rockets jets. We generally prefer not to use the rocket jets. They can
turn more quickly but we can't point them as accurately.

So in this case we use the reaction wheels to try and take our pictures.

Now the reaction wheels really can't turn the spacecraft fast enough to
match Enceladus' velocity when we're this close to it, angular velocity
when we're this close to it. In addition, it can't accelerate in an
angular sense fast enough to even catch up to Enceladus.

So the idea of a skeet shoot is the same as it is from the sport where
somebody throws a clay pigeon across the sky. And in order to hit the -
to shoot the clay pigeon, you have to raise your shotgun up and
anticipate where the clay pigeon is going to be ahead of your bullet or
ahead of your pellet so that by the time the pellet reach the trajectory
of the clay pigeon and they both intersect at the same point and, you
know, both basically arrive at the same point in space at the same time.

And this is the idea behind the skeet shoot that in order to make this
work we had to turn ahead of Enceladus quite early and ramp up the
spacecraft moving exactly the direction that Enceladus was going to be
moving across the skies.

And we had to wait for Enceladus to catch up and pass us by. And the
relative motion of the spacecraft and the camera was such it was slow
enough you could actually capture for a short period a series of sharp
images.

And by tweaking it we were able to move those images and allow
particular vent sites, as established by (Stefali) and (Porco) to pass
right in front of our camera when we wanted to take those pictures.

Okay, so let's go on to the - and I sort of said what the next slide is
all about. So let's go on to the slide after that.

Okay, the first skeet shoot was E4 fly by on August 11. And what I've
got here is a diagram that sort of summarizes what we tried to get and
what we I think we pretty much succeeded in getting.

And so that purple line is the terminator. We're looking at the South
Pole of Enceladus and this sort of cartoon. So the terminator is the
demarcation in the illuminated and the shaded, the shadowed part of
Enceladus is on the right.

So the spacecraft when we first will start taking pictures, we just
crossed the terminator and that picture labeled 1, we were able to
obtain about 8 meters per pixel.

And as we moved further and further, the spacecraft moved further and
further away from Enceladus, of course the picture gets slightly, you
know, more and more lower in resolution.

So we start out at 8 meters per pixel and by the seventh skeet shoot
image, that's about all we we're able to do in a skeet shoot sense. By
that time were up to 28 meters per pixel. But all of these that you'll
see were very valuable.

Now the site that - the actual vent eruption site that we triangulated
by (Stefali) and (Porco) are shown in red. So we were able to catch at
least four of those different sites. And we'll see those in one moment.

If we go to the next site, you know, the next slide, there was a second
skeet shoot on October 31. And this is a cartoon similar to what the
previous one was. Only in this cartoon we have the benefit of having
seen this area as a mosaic at a little bit higher resolution.

So in this case we start off with some more skeet shoot images than we
did in the previous flyby. And if you look towards the center you'll see
skeet shoot image number one was about 8.6 meters per pixel. And then
they project it would progressively grow to lower and lower resolution
until we finally get up to skeet shoot Number 9 which is about 39 meters
per pixel.

As - so we got a nice selection of the hotspots once again or of the
eruption site. And so let's see I think it's probably about - you'll see
there's one purple image, or purple graphic box at the bottom. That
wasn't a NAC image.

We were so close to the surface at the time we took that that we
couldn't get an image with an NAC image but the WAC, the one that's 10
times worse resolution still managed to get us a pretty decent shot in
which we got the plume site Number 5, event site Number 5.

Okay next slide. Okay, what I'm going to show you here is sort of - as
you probably noticed from some of the - those previous cartoons, these
images - we tried our best to sort of make these images fit together
almost like a mosaic. So we can actually get a sense of the terrain and
how it varies across the tiger stripes.

Okay, if you look at the for instance on the left, this is from the
first - both of these actually are from the first flyby, the first skeet
shoot setup.

The tiger stripes themselves, we've identified the twovent sites, 1 and
5. One on - all these tiger stripes have names so there's - and they're
all named after 1001 places in 1001 nights, so Baghdad, Sulci and Cairo.
So you'll hear a lot of Arabic names here.

Baghdad and Cairo though are two of the tiger stripes where we know
there are eruptions taking place. So 1 in 5 actually so we've nailed
the - we've nailed two of the sites right on.

You see here are the tiger stripes. There are about -with those raised
planks they're about 2 kilometers across to give you some sort of a
scale.

When you look at these target stripes closely you'll see that there are
sort of upraised planks that lead to the central valley.

And one thing we hadn't seen before in the valley forest were things
that people when they look at there's sort of very narrow ridges that
stick up hundreds of meters. And they may only be about 100 meters
across. So many people on our team they look like shark fins.

So you have tiger stripes and shark fins. It sounds like a bad science
fiction movie but we took a lot of interest in trying to figure out what
these things were. And we'll talk a little bit about that later.

But essentially what you see here is that where the eruptions are
occurring, the tiger stripes planks at this scale appear relatively
smooth. And when we look closer you'll actually see individual eyes
block sticking up.

But one thing we did notice is that wherever there was an eruption site,
pretty much we saw the same type of surface texture. We saw sort of a
smooth area, almost a fluffy looking area which was a blast up to 10
meters in diameter, maybe a few 10s of meters.

And we noticed that these tiger stripe rifts at the - had narrow ridges
extending up from the floor. Sometimes you can see they sort of - those
ridges sort of clump together like a bunch of grapes. And you see an
example there on your - in your Baghdad okay?

There are some other screens also visible here. You'll notice some
things that look sort of like ropey bands. And these are sort of
either - they basically occur in-between the tiger stripes. They're a
little bit from the stuff that you see near the top of your Baghdad on
the other side which is a more complexly fractured terrain that we've
come to call reticulated planes material.

On the right side here you see Damascus where we have a tiger stripes,
the hotspots 2 and 3. And again, you see this ropey terrain below. And
above you see the ropey terrain grating into sort of another kind of
strange looking smooth terrain. And it turns out these features coming
up from the top are old tiger stripes that are actually extinct. They're
no longer active. They're not embedded in this ropey type of terrain at
all. They too have been inactive for a very long time, probably won't
talk too much about that. We'll focus for the most part on tiger stripes
themselves.

Go to the next slide okay, and this is again one of our better mosaics
of Damascus-Sulci, showing the tiger stripes showings some details of
two of the hot spots.

And again what you see when we look up close is we see that the, for
instance, the inner walls of the tiger stripes are sort of striated. We
don't know if it's striated because for instance there may have been
boulders or blocks sliding down slopes. Or for instance those slopes
are - were scoured by the vent eruption themselves.

I would - my own personal prejudice is that they were - they represent
tracks of boulders that have notched down slope.

Again, you see this sort of knobby looking roping material, or ropey
looking terrain that forms bands that run very crudely parallel but not
exactly parallel. They're sort of curvilinear. But they have scales on
the order of a kilometer. They're similar in scale to the size of the
individual planks of the tiger stripes.

Okay, go to the next slide. And this again shows a close-up of Baghdad's
focus and one - of hot spot Number 6. And here we actually get a fairly
good look at the clump of these shark fins where they seem to be sort of
clumped together.

And you can see that they seem to follow to the edge of the fracture or
the rip floor. And they formed -they're almost lens shaped. They are
like shark fins with - we would use the term - a geologist would use the
term lenticular as in lens shaped to describe the shape of these kind of
odd ridges or hills.

And again this is - to either side of this tiger stripe you can begin to
see more surface details of this ropey terrain. You know, that's still a
bit curious to us.

Okay finally we get to lens sight Number 7 in - near Baghdad focus. Of
all the event sites, this is one that doesn't seem to have landed
directly or emanated directly from a tiger stripe. It's in an area
adjacent. And it's also near the distal end of a tiger stripe. It's not
near the middle. And it's not close to where these other guys were.

It actually is starting to get into this terrain that's not so different
from the terrain that we saw in 2005. This is an area of terrain that we
call reticulated terrain. It's a very highly fractured terrain that
exists at the - near the tips of the tiger stripes. And that's probably
what I want to say about this. Let's go on.

Okay, now I've sort of progressively moved up in detail here. I want -
what I want to show is sort of the two closest images, the two highest
resolution images that we got out of these skeet shoots.

The first one that I'm showing you is actually from the second skeet
shoot. This is our 9 meter per pixel image again showing the detail of
the ropey material that fall in between tiger stripes.

And we can see here that it's fractured right down to the limit of what
you could see. The fractures are very often sub-parallel. They sort of
break the surface up into the sort of little fading ridges.

Over the surface of this, over the tops you see lots and lots of little
blocks. And occasionally in areas you can see little smooth deposits.

So if you were to ignore the topography here you might the first order
say that imagine that the blocky materials that are distributed over
these terrains so this terrain - may not be looked at much different
than the blackened material that we saw a little earlier from 2005.

So you have to imagine what this scene would look like if you didn't
have the ropey terrain there, just the material that's sort of spread
over the top or spread throughout.

Okay, so now we'll go down to the next - we'll - I'm sort of mentioning
this because we'll look at it a little later okay.

Our first skeet shoot image on our first skeet shoot it actually ended
up being about 10 meters per pixel. It was between an Alexandria focus
and Cairo's focus \-- two of the tiger stripes.

Unfortunately we were very close to the terminator here. And so what you
see are a lot of shadows. But in-between the shadows you see a pretty
good glimpse of some variations of what you see in surface details.

Up in the upper left-hand corner I think that may actually be - I
haven't really pieced together where that is. It looks actually like it
might be the extension of a - the outer plank of a tiger stripe. And
you'll see there are individual blocks there. But there are also smooth
deposits along these planks.

So we may be near enough in this case to a active region in the tiger
stripes. But it to - you know, it just represents this type of fluffy
material spattered with blocks of ice.

Down more towards the lower left again you see an area that's somewhat
of hummocky with a large distribution of blocks spread over these ridges
and valleys that are caused by - are produced by this ropey looking
terrain.

Okay, finally, you know, to really get down to the best details, what
I've done here is just tried to take - if you go down to the very -in
this last slide, the very lower right, I basically projected all of
these images. So they're about the same scale. And that is the same
scale that the image that we saw in 2005 is in the panel labeled P.

So we're basically seeing these at all the same scale. Just a cursory
look at these and the size of the boulders. For instance, the size of
the ice blocks, your eye at least tells you that there's not a huge
difference. We're covering fairly a broad expansion of South Pole from
the, you know, centers of the tiger stripes all the way out to the
distal edge. In all case boulders and at least in many cases we also see
localized fluid deposits.

We do see variations in texture. For instance, particularly in the
funicular terrain or the ropey terrain, the one that's labeled C and D
you can again see little plates of material that have been fractured
sticking up.

We're in the process - we've had this data not long enough to really do
a thorough analysis. But this - as you can see, it's a very rich mine of
information. It's maybe, you know, no more than a couple dozen pictures.
We're going to get a ton of science out of this.

Let's see. I think - okay, very last is we were maybe a little too lucky
in taking these skeet shoot images. We were trying to see all of the -
all the hot spots we could, all that - I keep saying hot spots. I'm
going to talk to you about that in a minute - all of the - all the event
sites that we could. And we saw them.

But what we were lacking were a lot of images of things that were not
active. And so one question was can we find anything on a tiger stripe
that looks like it may be older for instance and maybe has a different
surface texture, maybe a different a gradational morphology, a
gradational structure that suggest that as tiger stripes get old they
may change their appearance and they may develop different
characteristics.

So there is one little branch of something that looks that way on this
image of Baghdad. This is again a mosaic you saw before. On the right I
just colored in the different terrain units. And you'll see a little T.
On the left I colored in the terrain units. And you'll see a key for
these different types of units.

I'm not going to go in detail about this. But I will point out that when
you look at the fresh tiger stripes, the active tiger stripes, you see
these smooth deposits are painted red. And down where they appear to get
older, you see distinct looking\....

When you look at those close up, okay, the smooth material as we were
talking up before, there's a fluffy deposit with blocks and boulders
spread over them. But the fluffy material, this was filled in and all
the - any cracks you might have seen.

As you move towards this area that's more of a clay deposit and you look
up close, no longer are the little cracks and little structures steeped
on the surface buried by fluffy stuff. It's you begin to see the cracks
penetrating through are not even being buried by puffy stuff.

There's some indication that as tiger stripes get older they cease to be
covered with this fluffy material. And they begin to develop more of an
armored or plated appearance.

Okay, let me go to the next slide. Now as you imagine, these shark fins
really sort of captured our imagination. It was - there was a heck of a
lot of discussion, exciting discussion on our team when we saw these
images about what are the ace things, you know, what might they be.

There were a lot of thoughts that well perhaps they're spatter columns.
They're deposits of sticky ice for instance that might have been vented
from the cracks pulled together or falloff in the valley.

But - and some of the people on our team who do dynamics calculations
say well, you know, based upon the thinness of the plumes that people
are measured, the dynamics that we calculate, that doesn't seem to be
too feasible. It's a theory or a hypothesis that we might need to think
about.

But in searching the literature we came across a feature that the oil
field people are familiar with called a positive flower structure. This
is especially interesting because it occurs in an environment where
there is both sheer and compression.

In other words, if you imagine that one side of a tiger slide -tiger
stripes can slide against the other, sort of like the San Andreas fault,
at the same time it's getting - you know, it can be pushed, you know,
and smashed together. Then material that's in-between, that's actually
caught in the cracks or maybe even making up the walls of the tiger
stripe can be extruded out or squeezed out like toothpaste.

And it turns out that there are features that are sort of reminiscent of
this on the earth called positive flower structures. And they have
sometimes have a characteristic shape. They look like little - you know,
you can see the cartoon there. They're sort of like little loaves of
bread that are lined up.

And I couldn't help noticing that some of our clumps of these dark fins,
they're a rather remarkable resemblance to this. As you can see in the
cartoon, these loaves of bread are sort of separated by diagonal cracks.
And I would argue that you could probably say the same thing about the
shark fins on the right.

So this is really interesting from a theoretical point of view because
there are a lot of theories right now trying to explain where, you know,
what the role of title flexing of Enceladus might be in controlling
whether or not the eruptions take place at a particular time if during -
for instance, as during certain times Enceladus orbit around Saturn, if
the tidal texture of the surface opened some fractures and not others.

One of the theories, one of the hypotheses right now that's been
advocated by (Nemo) et al. and Papalardo et al. and some others is
actually that sheer heating, that actually this rubbing of the walls of
the fracture against each other during tidal section could produce heat
would release some of the water vapor that we're seeing in the plumes.

And so what we're looking at if these are indeed positive flower
structures, these are materials that would be extruded and produced by
the same mechanism that this theory of sheer heating proposes.

And so I think that's we're just - again, we have a lot more to think
about. None of these are conclusive. But I wanted to point you in the
direction of where we're going.

And for those of you who want to tune in or at least look up on the Web
in December we're going to probably be reporting some more interesting
results at the American Geophysical Unit in San Francisco. I'd like to
turn it over to John Spencer. Thank you.

John Spencer: Okay thanks Paul. So I'm going to be reporting on the
observations for the CIRS instrument which is a very different kind of
beast to the visible camera that Paul's been talking about.

And just looking at the PDF, this just continues on into the next slide
after Paul's last slide. If you're looking at the PowerPoint it's a
separate file. So I hope you can find this.

So the first slide after the title slide shows a picture of our
instrument, the composite infrared spectrometer. This is built - got a
space flight center in Maryland. And it's operated from there.

And what this instrument does is its measuring the long wavelength heat
radiation from objects in the Saturn system.

And so the wavelength range is - starts about 7 microns which is about
14 times longer wavelength then visible light and goes all the way up to
300 microns. So it's a very wide range.

And we're not only measuring the total amount of radiation, but we're
obtaining spectra. So we're getting a lot of detailed information on the
wavelength distribution of the infrared heat radiation that we're
seeing.

And CIRS was designed to mostly to measure the competition of
atmospheres or the atmosphere's of Saturn and Titan. And it's very good
for that. But when we're looking at the satellite surfaces areas icy
bodies without atmospheres like Enceladus, instead what we're looking at
is simply the temperature of the surface and the heat radiation that is
given off by the surface just as a function of its temperature. And that
allows it to determine the surface temperature from the infrared
radiation. So that's a nice thing to be able to do.

So the next slide shows why we got excited about Enceladus from a CIRS
point of view. On this same flyby that Trina was talking about in July
2005 we got a good view of the South Pole and infrared light. And the
image in the lower left shows our view there. And its color coded by the
apparent temperature of the surface.

And you see basically we are seeing temperatures around 80 degrees
Kelvin which is about what you'd expect for sunlight warming the
surface.

But then down near the South Pole we have considerably higher
temperatures. And these are very hard to explain by sunlight warming the
surface which is what we see everywhere else in the Saturn system.
There's no particular reason why the sun should be warm down -
particularly warm in that region.

And it was pretty clear that we were seeing heat coming out of these
tiger stripes that Paul has been talking about. And this is not -
nothing to do with sunlight. It's heat coming out from the interior.

And we saw this again in November 2006 in a distant fly by. And that's
the image in the lower right. And from these operations by looking at
the spectrum, we could see that actually we were getting temperatures
like a lot higher than would be apparent from the simple images.

f you actually look at the wavelength distribution of the radiation we
seem to be seeing temperatures up to about 145 Kelvin which is, you
know, about minus 200 Fahrenheit. It's still very cold but it's much,
much hotter than the 60 or 70 Kelvin that you would expect the surface
to be in this region. As is indicated, there's a lot of heat coming out.

The next slide shows the press release we did back in 2005 where the
imaging team showing one of these images of the tiger stripes with a
temperature scan superimposed on it with our instrument, the CIRS
instrument there.

And you can see the temperatures are quite a lot warmer looking right at
the tiger stripe than they are off to the side.

So we didn't get another close look at Enceladus until this year. And we
since then we've had four flybys. And we've got data from the CIRS
instruments on all of them.

The one that was actually most interesting for us is one that Paul
didn't mention which it is from March 2008. The reason Paul didn't
mention it is because when we flew back to Enceladus then the moment we
flew past Enceladus pretty much it went into Saturn shadow and it was in
the dark. And that meant there was no sunlight falling directly on the
surface and it was very hard to take images. But that allowed us to
look - have more time to look in the infrared of the heat radiation
coming out of the fractures.

And so the next slide shows the temperature map from July 2005 with the
green lines showing where the tiger stripes are. And you can see that
the warm areas shown by those covered contours pretty much corresponds
to where the tiger stripes are.

But the large red rectangle is showing kind of the finest detail that we
could see of that observation. And it's barely enough to separate one
tiger strip from another. And it all gets kind of merged together. And
you're missing a lot of detail.

So on this March 2008 flyby on Orbit 61 we we're able to get much higher
resolution. And the little rectangle or the little square is showing the
typical resolution that we got on that fly by.

So we were able to map the distribution of the heat radiation in much
for detail. And then the larger red trapezoidal shape shows the area
that we were able to scan at high resolution during that fly by.

So the next image is the result of that scan. This is now an image that
we took by combining the visible wavelength not from the imaging camera
with the heat radiation seen by the CIRS instrument.

And you can see now which fractures are warm and which are not. And you
see that there is heat coming out of these fractures all the way along
the length but variable amount of heat that the -some parts of the
stripes are a lot - the tiger stripes are much warmer than others.

And it's interesting actually to compare with what Paul was saying about
active and inactive tiger stripes.

We can see directly from the heat radiation, which tiger stripes are
active and which are not.

It if you were to look and go back to your longitude grid here at about
1 to 2 45 which is about 4:30 clock position from the pole down around
80 degrees south, there is a fracture which Paul was showing had a
slightly different texture. And you can see there is no heat coming out
of that fracture. You can see the images but it's not producing much
heat. So if that can be it is an inactive fracture.

And again, if every point along these fractures we were able to make the
temperature and we got temperatures this time up to at least 180 Kelvin
which it is quite a lot higher than we'd seen last time, not because it
had got warmer but simply because we got a better look.

The next slide shows the same data in a little bit different form. The -
this is now showing the data at its full resolution. The previous image
we've blurred it out so you could get a pretty good picture.

But when you don't blur it you can see a little bit more detail. And you
can see the variation in temperature along the fractures.

And now I'm showing where the plumes are that (Stefali) and (Porco) had
seen where the gas jets were coming out, at least the most prominent gas
jets.

And you can see that the - those are marked by the white stars. And the
numbers and the numbering scheme is the same one that Paul was using.

And you can see that the gas or the dust jets and by the cameras, tend
to fall along the active stripe and tend to fall in the most - in the
warmest regions of those stripes. So it's not a simple relationship.
There are some warm areas that don't have jets.

So the next slide shows the next time we flew past in August 2008. We
could politely if Paul's finished with his skeet shoot and get all those
beautiful high resolution images.

And then we did a scan with our instrument. And by the time the imaging
was done we were quite a lot further away. So this isn't quite so
detailed. But you can still see as we've crept across we picked up the
heat radiation from each of the four tiger stripes. And we see pretty
much the same distribution as we saw before in March.

The next slide shows how we compared the distribution from the two
times. This was very interested to see are these fractures very steady
in their heat output or are they varying?

And so we divided the heat radiation along each of those fractures into
each of these boxes and added up how much heat was coming out in each of
those boxes. And then in the next slide we plot the heat distribution
along the tiger stripes on each of the - well along each tiger stripes,
so those two flybys, the one in March 2008 and the one in August 2008.

And so we -now we can get a bit more quantitative and we can see very
consistent distribution in most cases.

But the Baghdad tiger stripes, there does seem to be a hint of changes
between the two flybys. And we - we're still looking at this in more
detail and trying to convince ourselves whether this is a real change or
just a result of a measurement limitation.

And then the next slide shows the temperatures along the tiger stripes.
We were able to measure the temperature in each of those boxes
independently of each of the other boxes. And we don't really see any
obvious changes except maybe Alexandria is a little bit cooler. So we've
seen temperatures going on around 160, 170 Kelvin range in these
observations.

The next slide shows the data we got while we were riding along with the
skeet shoot that Paul was talking about from August 2008. And hear these
little, mostly blue lines show the area scanned by our detector at each
point along that scan.

And you see the length of those lines getting steadily bigger as you go
from the right-hand side to the left-hand side as we were pulling away
from Enceladus and seeing larger and larger regions as time went on.

And the blue colors are where it was pretty cold. And then the red
colors are where we saw high temperatures. And you can see that the high
temperatures are pretty much on the tiger stripes except interestingly
enough at Cairo where it's looking like the most active region is not
directly on the tiger stripes. It's off it a little bit. So we're seeing
some variability there, some things that you might not quite expect.

And then the next slide shows an observation that we did in cooperation
with the imaging team. And we asked Paul at the end of the skeet shoot
to position the spacecraft pointing such that our short wave length
detector was perfectly aligned with Damascus-Sulci which is one of the
warmest of the tiger stripes that we saw.

And we -so the images in the lower-right shows the ISS image with the
site of our detectors, a series of yellow rectangles superimposed on
that.

And you can see that Paul did a perfect job and got our detector
perfectly aligned along that - this warm part of the tiger stripe
somewhere between plume 3 and plume 2.

And in the image in the lower right which is our lower resolution data
from back in March which at the time we thought was really high
resolution, the area we're looking at is between the two stars on the
lower of the two tiger stripes. It's the area that is white which means
it's the hottest region that we saw. The two stars are the plume two and
the plume three sources. And we just straddled the region between those
and got a nice reading.

And so the next slide shows a spectrum where we're actually plotting the
brightness of the heat radiation from Damascus surface at different
wavelengths.

And I have to apologize that the wavelength scale is given an wave
numbers which is something most people don't think in those terms.

So technically a wave number is the number of wavelengths in a
centimeter. And 1000 wave numbers is a 10 micron wavelength.

But, so don't worry about that too much. But we're looking at the
wavelength range from about 9 to 16 microns here.

And you see that the smaller waves numbers which is longer wavelengths,
we're seeing more radiation. But it's dropping off very smoothly as we
go through the higher wave numbers or shorter wavelengths.

And we can fit that with what we'd expect a surface at a given
temperature to be radiating. And we can get temperatures quite
accurately from that.

And so in March in the top figure you can see we were getting
temperatures of 152 or 193. In fact, depending on what wavelength region
we were looking at.

And the number in meters tells you how much material along the tiger
sites would have to be warm to achieve this.

So you might have a couple of 100 meters at that temperature from 52
Kelvin extending all the way along the tiger stripes. And that's a small
enough region that it would fit comfortably in the bottom of those
fractures. Or the higher temperature I would guess an area of only about
30 meters wide at this higher temperature.

Now the bottom part, it blows this up so you can see, you can compare
the data we got in March which is the black squiggly line. And it's kind
of ratty because we weren't looking for very long.

With the data we got in August where we stared at Damascus Sulci and
those data are actually hard to see because they fit so perfectly under
the blue line with which is our theoretical model of what we would
expect.

And but you can see that black line that's got a few wiggles just poking
up from behind the blue line there. And that is a beautiful spectrum
that we got as a result of Paul's light pointing at the end of the skeet
shoot.

The puzzle is now if you look at that bottom slot whereas in March we
had seen temperatures about 193 which we said was above 180 just to be a
little cautious. Now we're getting lower temperatures more like 160. And
we're inclined to believe the new temperatures rather than the old
temperatures because the data are so much better.

And if when we look at subsets of that data we actually see temperatures
up to about 167. But in these new very high quality data that's about
the highest temperatures we're seeing.

So these are still pretty darn warm compared to what you'd would expect
of the South Pole of Enceladus not quite as hot as we thought before.

And trying to make sense of these temperatures and see what might be
happening underneath the surface, you have to start worrying about the
physics of what's going on beneath the surface.

The fact we're seeing temperatures up around, you know, at least 160,
170 on the surface, means it has to be warmer down below. And we really
want to know how much warmer, particularly does it get warm enough that
the ice can melt and we might have liquid water down there that could be
a habitat for life. And so allows a lot of interesting things to happen.

So the model we have here is we simply see we have a crack at a
particular temperature. And then the heat spreads out from that crack
and it warms the surface around the fracture and allows you to determine
what the heat, the temperature of the surface would be and therefore
what the heat radiation would be.

And the little example in the lower right shows the vertical slice
through a crack. And the crack is in the middle of that red triangle.
And it's here it's just a melting point of water in this view.

And so you can see that the surface temperatures are quite a lot warmer
than - cooler than that. And from that red color indicating very high
temperatures we've got blues and greens on the surface. But from those
you can infer the higher temperature.

And the green curve now superimposed on the actual spectrum shows the
best fit we can get to the data with a model like this.

And we can certainly with temperatures that are a little bit lower than
the melting point, more like 225 degrees Kelvin. And have we have three
of those, a few 100 meters apart or maybe up to a kilometer a part, we
might be able to fit within the tiger stripes. Then you can actually fit
the spectrum pretty well.

So we're working more on improving these bits and getting a better
understanding of what's happening underneath the surface.

And that is the story so far. We have data now from the two flybys in
October where we got more very nice maps, the distribution of the heat
and more spectra. And we're working on those and hope to have something
again to show at the AGU meeting in December.

And that's it for me and I can now hand over to Sascha.

Sascha Kempf: Yes, thank you John. So my task here is to talk about the
dust particles, what we can learn from dusk particles you'll find in the
vicinity of Enceladus about the processes going on on the surface of the
moon and in the interior of the moon.

In the dust instrument is even more different from a camera then the
CIRS spectrometers. And the first slide shows you how the dust analyzer
looks like. And the purpose of the instrument is to measure the dust and
the mass and the impact speed of dust particles.

And dust particles here means particles of a size range of a few
nanometers up to let's say 100 microns. That at least as the largest
particle we ever detected. And the impact -speed, the surface impact
speed of a particles, which are in a system on the order of 10 meters
per second. But by means of this instrument we are - we can basically
determine the impact of speed in a range between a kilometer per second
and up to 100 kilometers per second.

And this instrument's quite similar in some aspects to the instrument on
Galileo and Ulysses. But in contrast to them, to these instruments this
instrument also includes a simple time of flight mass spectrometer.

So the essential principle is that the particle hits the spherical
targets at the bottom of instruments. And as a consequence of the impact
the particle is transferred into a mixture of plasma and neutral gas.
And the plasma is then separated in strong electric fields. And the
positive ions are accelerated towards the texture in the center of the
instrument, the star-like thing. And from that we can measure the time
of flight of the ions. And this gives us an idea about the composition
of particles.

This instrument is also capable to detect or to measure the charge on
the particles. That's a very important quantities on the dynamics of the
particles is strongly influenced by the planetary fields of Saturn. And
you have to know the charge carried on the grains in order to get this
specific approach modeled correctly.

This instrument which is based on the impact ionization phenomenon can -
is capable to detect at least with standard software of the order of one
impact per second. And this detection rate is not sufficient for the
interior of the E Ring where the impact may be of the order of 100
impacts per second as during the previous flyby it detected up to 50,000
impacts per second.

In order to do measurements or to determine at least the impact rate in
such a dense dust rich environment, there is a small detector piggyback
on our instrument that is a tiny clear box with the two black circles in
front of the instrument. That's a so-called high rate detector.

And this instrument detects particles by means of the damage they do to
two foil, a thick foil and a thin foil and basically to polarization of
the foil. And this change, the capacity of the foil can be measured and
allows us to take or to measure impact rates up to 10,000 particles per
second.

Okay next slide. What I actually wanted to tell you in my part of the
presentation is what you can learn from the dust measurement in the
vicinity of the moon.

Okay, the question one should - you should ask when looking onto the
famous plume picture is, is the plume phenomenon as it appears on the
images is actually what you expect how such a plume should look like.

You may be tempted to say yes I expect such a shape but this actually is
not - that's not true.

The problem is that we know pretty well that the speed of the emerging
gas from the cracks is what measured by two instruments by the neutral
gas spectrometer, item S, and by the ultraviolet spectrometer UVIS.

And we know that the gas speeds or the speed of the emerging gas on the
order of 500 meters per second.

And we also know the density and - of the gas and we also know the
amount of gas emerging from the moon.

And now suppose that the gas is escaping from within the cracks through
the exterior. Then the slow speed of the gas which was it's found to be
on the order of 500 kilometers will also transport - the gas will also
transport - and the dust particles, the ice particles.

So right now we don't care how the ice particles are formed. It's just
the fact that the ice particles are transported via the gas stream from
the interior of the moon to the exterior.

And the gas conditions are such that dust particles of micro meter size
\-- and it's the typical size of a dust particle injected by the moon
\-- that these particles coupled stiffly to the gas stream. And what you
expect to observe is that all dust particles escaping from within the
moon should have the same speed as the gas jets.

And the gas jet speed themselves is higher than the escape speed of the
moon. So what you actually expect to observe is not this kind of plume,
the stratified structure which is denser, closer to the surface and gets
more diluted at higher altitudes, what you expect is a kind of a jet and
expanding into the system. And that's not what we see.

And this fact tells you something about what's going on inside the
cracks. Since what you have to explain is how do the particles decouple
from the gas stream and acquire significantly lower speeds than the gas
speeds of the already formed plume?

And the answer we gave to that is that we propose that inside the cracks
which are bumpy, curvy, the particles collide with the walls. And when
the particle collides with the wall then the particle is stopped. The
particle decouples from the gas flow.

And as a consequence of that, the speed of the particles gets modulated.
You get a dependence between the particle size and the speeds of the
particles escaping from the cracks.

And this can be modeled, this can be expressed in terms of the assumed
size or rifts of the crack. And to our surprise that there are only two
parameters which describes the phenomenon. The first parameter is the
size of the small structure and the second parameter is the ratio
between the opening of the crack and the depth of the crack.

And this can be used - next slide please - to determine the conditions
inside the cracks, since which you find from such model calculations is
that assuming reasonable opening sizes of the cracks and reasonable
dynamics of the cracks it means that the crack is expected not to be
deeper than the size of the moon - things like that.

If you find relations between the parameter and the temperature inside
the cracks and the consequence of the model is that inside the cracks
has to be a temperature close to the melting point of water.

So the shape of the plume, the morphology of the plume, that dust
particle density measured by the dust instrument, the gas entity
measured by the neutral gas spectrometer and the appearance of the plume
itself, if you all put together you end up with the scenario that such
phenomenon actually requires temperatures inside the cracks on the
bottom of the crack which are close to melting point.

Okay, next slide.

What we also did, we looked into the ejection process of the emergence
of the particles into the E Ring. So this image shows you the plume and
the alignment of the particles ejected by the plumes ring flame.

And obviously since the dust part is in the South Pole area of the moon,
the particles are ejected preferably in a minus direction of the ring
flame. And there's only a certain number of particles which are ejected
faster than the escaped piece of the moon. And only these particles can
populate the E Ring which is set by the moon.

Next slide. And we performed numeric simulations of the particle
ejection process where we put in everything we know, as we knew about
the locations of the duster, which were determined by (Stefali) and
(Porco). We put in the interaction of the particles with the
electromagnetic field. But since we know the charge and the evolution of
the grain charge the model also includes the disturbance by the gravity
field of Saturn due to the flatness of the moon.

And we used at the initial conditions of the ejected dust particles the
speeds and the mass distribution of the particles which were derived
from by means of the model I explained at the start of my presentation.

And when you use this model you can determine the vertical profile of
the E Ring in the vicinity of the moon. This is shown on the next slide.

What you do is you simulate the ejection process by means of first
principle. You assume that the particles are ejected from only the jet
sources identified in the images. And you end up with the ring profile
what - which almost perfectly fits the measured ring profile by means of
the dust detector.

So this block shows you the dependence of the impact rate from the
height above and below the ring plane. And the solid line shows you the
prediction by the model.

And the match is almost perfect. And the consequences or the meaning of
this fit is that actually the spikes in the models of the individual
dust jets on the surface of the moon.

So this means that from the vertical profile of the E rings in the
vicinity or at the orbital distance of Enceladus, you can actually at
least monitor the variation of the dust production of the various
individual jets. And you can also at least constrain whether the
alignment and locations of the dust jets on the surface are determined
correctly or if there are additional sources.

So since the spacecraft performed much more ring plane crossings then
close flybys at the moon, this provides us the unique opportunity to do
a long term monitoring of the activity of the moon. Next slide please?

So in order to demonstrate to you how well the model actually works,
this plot here compares the model predictions to the data CDA of the of
the cosmic dust analyzer obtained during the flyby in Orbit 11 in August
of 2005. And on the red symbols on these are the dust counts by the dust
detector. And the wide curve is the best fit or the best prediction by
our model.

And it shows you during this flyby, the spacecraft actually only crossed
two dust jets. The spacecraft actually flew only to the dust jets on the
Damascus crack.

And the - so it was really sheer luck that the spacecraft detected, the
instrument on the spacecraft detected during the fly by, the dust jets
at all since it is only a matter of a few kilometers. If the ground
cracks would have been shifted by let's say 20 kilometers we wouldn't
have observed a thing.

Okay, next slide. What you can also do with such a model is you can
actually calculate where the dust particles fall back on the surface of
the moon. And there's no surprise that most of the dust particles fall
back close to their - to the locations of the jets themselves. And it's
only a minor fraction of the particles, of the jet particles which
actually are capable to hit the surface in the equator environment of
the moon.

And this tells you something, such models tells you something about the
surface erosion of the moon by means of the infrared meters. This
basically tells you that everything you see on the surface, the erosion
processes can't be due to the dust particles since the impact rates are
way too low. Only in the vicinity of the cracks themselves, the mass
position by the ice particles is actually important and relevant.

So the other unique property of our instrument is that we can tell you
something about the composition of the dust particles. This is shown on
the next slide. Since Enceladus is the major force of ring particles
it's actually is efficient to determine the composition of the ring
particles itself in order to learn something about Enceladus.

And to our surprise we found that the ring particles are not pure
waterized, at least not all of them. This is what you actually expect
for such an environment.

There are actually four populations of articles. There is the first
population which are pure waterized particles. They are on the order of
40%, 50%. It's a little bit depends on the environment where we take the
particles.

The second populations are water ice particles within small organic or
rocky impurities. And that is inside - within the particles. And the
important point here is that this impurity is followed. It's not a
material imbedded in the matrix of the ice particles.

There's a third population which is a quite surprising one. And this is
a population of sodium rich water ice particles. And the fourth
population is an iron rich non-water ice population. And those
particles, they do not originate from Enceladus. They are probably even
of exterior origin. So but these populations only constitute on the
order of 1% to 2% of the ring particles.

So the next slide shows you the most abundant two composition types and
how such a spectra looks like. The population one, pure waterized. The
best explanation we can give for the origin of this particle type is the
surface of the Enceladus since the E Ring particles or the micro
meteoroids from the exterior of the Enceladus system which strikes the
surface of the moon, they produce fresh particles.

And since the surface of the Enceladus is clear, very pure waterized,
it's very likely that the particles that's used by this mechanism are
also - should also be pure waterized.

And the spectrums shown here shows you the typical appearance of a pure
waterized spectrum. And it's a cascade of lines, equidistance in mass.
And these mass lines are formed of the hydronium, ions and of neutral
water molecule.

And the second population, population two, waterized platinum purity,
first of all the difference in spectrum is quite apparent. There is an
additional feature of the mass around 29.

And the unfortunate thing with time of flight mass spectroscopy is that
there are some on the (Hutchon) wall. Since mass 29 can be attributed to
various types of materials or of molecules and atoms. So of course there
is silicon with a mass of 28. But it's also possible that certain
organic compounds have a similar - produces a similar mass line.

And the second feature in (Hutchon) mass spectrum is a feature at 42
which is probably potassium or a compound formed from the water
molecules with other constituents.

And in-depth analyzer shows that here the additional material inside the
spectrum has to be a solid material. It's not possible to produce such a
spectrum by molecules of the particles.

And so it's very tempting to propose that these particles, the
population two that they originate from inside the plume since probably
the best explanation for the production mechanism of the ice particles
is that the ice particles are forming and nucleating in the descending
water vapor inside the cracks. And the nucleation works far, far better
if there are tiny nucleation cores within the gas stream.

As soon as there are nucleation forms, water vapor starts to condense on
the surface of the nucleation core and forms dust particles.

So it's our best explanation if the population two particles are
particles originating from inside the cracks. And that's what our main
goal to determine during the previous set of flybys.

However, since the impact rates were that high, the mass spectrum of the
particles detected during the flybys overlaps.

And so our group is right now kept busy with disentangling the
overlapping margin spectra. So we obtain thousands of mass spectra. And
after deconverting the mass spectra I think the numbers will be even
higher. And then we can really prove this claim that we can distinguish
blue particles from surface particles and particles from other sources
inside the ring. This is then - can then be answered.

So if it's possible and we're confident that it is the case that you can
actually distinguish the particle or the determined origin of the
particles by means of composition, then you can do really exciting
things with the dust instrument.

Then you can for instance follow the transport of the particles inside
the huge - within the huge E Ring. You can determine whether
enhancements of dust at certain regions inside the ring is due to
particles originating only from one particular source or not.

You can study the mass transports to other moons, in particular to Titan
and to the other ice moons. And so give us perhaps another half a year
and we can give you a decent answer to the interesting question.

And my last slide just shows you what's - how the mass lines be observed
in our time of flight mass spectrometer actually formed since this is a
little bit confusing.

So what you actually expect when an ice particle hits a target is that
the material gets ionized. The molecules are actually partially
disrupted into their atoms or atomic constituents. And so what you would
actually expect are only a very small number of mass lines \-- hydrogen,
oxygen H2O or H30 plus.

But this is not the case. We observe much more mass lines. And the
reason for that is that within the impact rate that's produced by the
particle hitting the surface, the impact target of the instrument, again
a kind of chemistry is going on. So as soon - there are hydrogen ions
formed, the hydrogen ion tries to capture a neutral water molecule to
form the hydronium molecule and as soon as a hydronium molecule collides
with another neutral water molecule, then a so called cluster ion is
formed. And the cluster ions and can be very, very large.

And that's - this is what the mass lines are telling you. What you see
is actually clusters of unusual water molecules and hydronium ions. And
from the cluster distribution you get information about the conditions
inside the impact wafer. That's all that I can tell you right now about
our findings. Thank you so much.

Jane Houston Jones: Will thank you to all three of our speakers. I
have - this is Jane in Outreach. And I've received five questions that
came in through email during the talks. And if anybody else has
questions, this is a great time to ask.

I hope all of our speakers are on so we can thank them all. And if
anybody has any questions, go ahead and say your name and spell your
last name. That would help for the transcript.

And then I will - I'll ask my five questions that came in via email
after that. Anybody have any questions?

Well then I'm going to ask mine. These come from a Saturn observation
campaign member in Ireland, (Deirdre) Kellegham, K-E-L-L-E-G-H-A-M. And
one of her questions is, \'Have you been able to determine how fine or
course the plume particles are?\'

Sascha Kempf: That's probably a question for me.

Jane Houston Jones: Yes.

Sascha Kempf: Yes. We know the site distribution of the plume particles.
We determine the distribute - and the site distribution of the particles
already in 2005 when we flew for the very first time through the jets
themselves.

So the sizes of typical plume particles is ranging between 1/2 a micron.
And the largest plume particles are of the order of 3 microns. At least
we haven't detected a larger particle in the vicinity of this moon than
3 microns. And that's a quite narrow site distribution.

Jane Houston Jones: Great. The second question is are the outbursts
predictable like geysers on earth?

John Spencer: I could have a stab at that. We don't know yet. We have
some ideas that the jets of gas and ice that come out may be controlled
by the opening and closing of the fractures. And the fractures may open
and close every day in response to the tides of Saturn.

Saturn is pulling on Enceladus all the time and distorting itself. And
that's what generates all this heat. But that may also open the
fractures at some point in the orbit and let gas and dust out and close
them at other times.

And so you might predict from that kind of model that you would see
these periodic variations every day as Enceladus goes around Saturn. But
we haven't really seen strong evidence for that yet.

And beyond that, we don't know yet. We're seeing tentative evidence for
changes in the heat radiation and being some other evidence that things
are changing from one month to another. But it's not very certain yet.

We don't get to look at the plumes as often as we would like. And so
it's hard to get a really continuous picture of what's going on.

Sascha Kempf: Of course, I can add here that our model assumes a
constant production rate. And deviations of the model predictions from
the flyby results was never stronger than let's say a factor of 2.

And this tells you that also the production rate cannot fluctuate well,
stronger than of the order of - than a factor of 2. And that's quite
surprising.

Jane Houston Jones: Will that's great. That's nice. She has questions
that are coming to all the different speakers. The third one is has
Cassini been able to measure how deep the slits are within the tiger
stripes?

Paul Helfenstein. Our first measurements are just done from shadow,
projected shadows. And we were -basically these were the depth of the
valley. And they extended down, you know, hundreds of meters.

There's been work, phototronometry work from (Paul Shank) in particular.
He sees some tiger stripes that are maybe a kilometer deep.

Now that's a different question, that may be a different question how
deep the cracks actually penetrate into the surface. That we don't know
for certain. There's some idea - I've done - I have a paper that's
submitted right now and other people have done papers as well in which
we try and use the spacing of tiger stripes to mean like 32 to 35
kilometers spacing to estimate how deep the fractures penetrate.

Because as you might imagine, if you have tension on a flat plate, if
you imagine that flat icy plate to be near the South Pole of Enceladus
and you pull on it in both directions and produced tension, a fracture
forms to relieve the stress.

So once a fracture forms, the stress, the tensile stress in the vicinity
of that crack drops to zero. But if you started walking away from the
crack it could measure the way the stress builds up. Eventually it can
build up to a point where another fracture forms.

And so the spacing of the fractures is sometimes a clue to how deep they
actually penetrate.

And so estimates, you know, there's a wide actual range of estimates.
But people are saying something on the order of less than 10 kilometers
to a few tens of kilometers.

Jane Houston Jones: Great. Okay, the final question is - that came in
through email is do the particles come out at speed? Would they - would
you say they explode out under pressure or would you say the material
seeps out?

John Spencer: Oh, it's exploding out under pressure. These are
supersonic jets.

Jane Houston Jones: Great.

John Spencer: Yes. And you probably won't want to stick your finger in
one of them. Its - we don't have a real good handle on the speeds but
it's hundreds of meters per second definitely. And it's supersonic.

Sascha Kempf: That's the escape speed of the moon is 207 meters per
second. And that - this means that the majority of the particles can be
faster than that. Otherwise the particles would just escape from the
moon.

Jane Houston Jones: Right, right.

Sascha Kempf: And you wouldn't see a plume. So that's right that the
particles would actually populate the E Ring. They have to be faster.
But most of the particles escaping from the moon are ejected from the
vents \-- about 90%. They have to be slower than these escape speeds.

And that was the nature driver for the model we developed in order to
explain this discrepancy between the slow speed of the gas and the
apparent fact that there is a plume close to the surface.

Jane Houston Jones: Does anybody else have any questions?

(Deirdre)'s final comment is that the images from Enceladus are just
awesome. So I wanted to share that with the three speakers.

If - nobody else has any questions our next - we will not have a telecom
on in December because it's during the - it'll be like the - close to
the end of the year. And we never do have the December CHARM telecon.

And at this point we're looking for some suggestions for topics that you
would like to hear about that haven't been covered so far.

So if anybody has any suggestions for topics to cover, you can send them
to the CHARM leads email that is on each of the announcements that you
received.

And with that, I'd love to thank our three speakers for an awesome
presentation. And everybody have a wonderful Thanksgiving and holiday
season.

Okay everybody goodbye.

Man: Bye.

END