**FTS-NASA**

**August 30, 2005**

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

Coordinator Thank you for standing by. Today's conference is now being
recorded. If anyone has any objections they may disconnect at this time.
I'll now turn the meeting over to Ms. Trina Ray.

Trina Thank you. Welcome everyone to today's CHARM telecon. We've had
some very exciting fly-bys of one of the moons of Saturn, Enceladus,
recently. Two in particular targeted fly-bys, one in February and July,
and joining us today to talk about some of the recent results is Dr.
Larry Esposito. He's the principal investigator of the Ultraviolet
Imaging Spectrograph, and unless I'm mistaken, Larry, you're joining us
from London, or did you decide to stay home?

Dr. Esposito I came home from Cambridge, I got home last night. So, I'm
joining you from boulder, Colorado.

Trina Okay. Well, take it away, Larry, and thank you very much for
joining us today.

Dr. Esposito Thank you, Trina. Everyone who's online, hopefully you're
looking at my first slide, which says "Enceladus Eruptions," and
identifies me as the principal investigator of the UV Imaging
Spectrograph. If anybody's having a technical challenge at this point,
inform me of that, otherwise I'm going to just proceed here with the
slides that I have in my presentation, which, as Trina said, is some
very recent and very exciting results about the tiny moon Enceladus, a
moon of Saturn. If we go to the next slide, I want to remind you that
some of the mysteries that we now are aware of about this moon,
Enceladus. It turns out that it's the shiniest object in the entire
solar system, it's very reflective, it's a bright object, maybe as
bright in some spots as newly fallen snow, and even before the
spacecraft had visited Enceladus one of the mysteries was how it could
be so bright and shiny, because space is a place where there are things
that are always degrading and darkening. The radiation in the Saturn
system, sunlight, meteoritic bombardment, all would turn clean surfaces
very quickly into dark and dirty surfaces of satellites and rings. One
of the things that's a little bit of a mystery, particularly about
Enceladus is why it is so bright, but I think we may have a partial
answer to that based on the new Cassini results, and that is that it's
bright and shiny because the material on the surface has not been
exposed very long to these darkening agents.

The second of the mysteries has to do with the geology of Enceladus, and
we got our first clues about this when we flew by with Voyager more than
20 years ago, but now the close-ups of Enceladus show very broad plains
that have no craters on them. The process of bodies in the solar system
striking the surfaces of moons and planets has been going on for
billions of years, and we see the results on our own moon, where the
ancient surfaces of the moon, particularly the highlands, are completely
covered by craters, one crater on top of another, and the lava plains,
the Mari, the seas of the moon are cratered but much less, showing that
they're younger than the ancient highlands. In the same way, when we see
these broad plains that have no craters on Enceladus we know that
they're very young.

Another mystery has to do with the location of Enceladus at the center
of Saturn's E-Ring. This is a very thin ring, and it's not obvious yet
that we have clear pictures of it from Cassini, but it's been observed
from the ground and it's a ring that's unlike the other rings of Saturn,
which are broad and bright and seem to be made up of very small
particles, spread both in distance from Saturn and above and below
Saturn's equatorial plane. But amazingly enough the moon Enceladus, a
tiny moon, is at the center of Saturn's E-Ring and we've been searching
for a connection, maybe a connection that's now becoming apparent to us.

The fourth mystery which I want to mention is that just a year ago, as
the Cassini spacecraft approached Saturn, the spacecraft made systematic
scans, mosaics, pictures, of the entire Saturn system. These scans were
analyzed by the Ultraviolet Imaging Spectrograph team and we were able
to identify a cloud of oxygen atoms around Saturn, and we were able to
see these because of the characteristic light that's shining from these
oxygen atoms, it's like a fingerprint. The spectrum shows strong
emission, had a wavelength of 1304 angstroms, which can only be produced
by oxygen atoms. The number of atoms we discovered was many more than
people had expected, and surprisingly enough, the distribution, the
number of oxygen atoms also showed a peak near Enceladus' orbit.

I'm moving to my next slide, which is about the first clues that Cassini
had of something more exciting happening on Enceladus. On the 17^th^ of
February 2005 we had a close fly-by of Enceladus, and Cassini's
magnetometer detected a bending of the magnetic field around Enceladus.
Now, this may seem a minor or maybe even a negligible discovery, but the
magnetic field, like an electromagnet, or the earth's magnetic field, is
excluded by conductors. It looks as though there was a conducting layer
surrounding the moon Enceladus, which the investigators hypothesized may
have been a result of ions formed by sunlight falling on the atmosphere
of Enceladus, if it had one. So the idea was that there might be an
atmosphere around Enceladus and light from the sun would be removing
electrons from some of the atoms in the atmosphere, making them
conductors, and those conductors would exclude the magnetic field from
the region around Enceladus. This was a very exciting indirect
indication that Enceladus might have an atmosphere, and the project
decided to reinvest some of its resources and to re-plan a later fly-by
of Enceladus, which was scheduled for July of this year, to fly very,
very close to the moon, to fly within 175 kilometers of the surface of
Enceladus.

Now, Enceladus is not a big object, it's only 500 kilometers across;
that's 300 miles. If I got into my car here in Boulder I would be in
Nebraska in a few hours, and that's about the distance, the size of the
whole moon Enceladus, so it's a tiny moon. It's not expected to have an
atmosphere. It's not expected to have any sort of geologic activity. In
fact, it's expected to be just sort of an ice cube that's been sitting
around Saturn for four and a half billion years and gradually ground its
surface, ground down and marked up and dirtied by meteorite impacts, and
covered with craters. We knew from the first that it wasn't what we
expected, but we didn't know exactly why that was the case.

I'm moving to my next slide, which is a demonstration of the effect that
was seen by the magnetometer, and what you're seeing here are these
yellow arrows and lines and all that yellow stuff is truly invisible,
it's a representation of the Van Allen belts of Saturn, which are
trapped by the magnetic field. As the moon, Enceladus, which you can see
on the right, moves around Saturn and moves through that magnetic
environment, mostly without any trouble, except if there might be some
cloud near Enceladus.

Here are the artists' drawings, and you can see on the diagram how the
lines of magnetic force have changed their location. The lines of
magnetic force are excluded by the neutrals in the cloud, which is shown
here near the southern pole of Enceladus; that's a point we didn't know
yet, so that already in February we had some indications that Enceladus
was unusual and the project used some of its capability to readjust the
mission to aim for a close fly-by of the moon in the month of July. So,
Cassini was redirected to fly within 179 kilometers of Enceladus on the
14^th^ of July 2005.

We see the pictures here, the ISS color mosaic of Enceladus on Rev. 11,
which was the eleventh orbit the spacecraft had made around Saturn, and
in the month of July, at the closest approach to Enceladus, it took
these pictures. Now, if you look at this picture, you'll see some very
interesting things. In the upper right hand part of the moon you see a
number of craters, bowl-shaped depressions which are caused by meteors
that have hit the satellite.

On the other hand, on the lower right there are no craters to be seen at
all, instead there are these stripes that go upper left to lower right,
the imaging team members have called these tiger stripes, they resemble
the stripes on a tiger. The parallel stripes were unexpected from
earlier images and show two things; they show that there's been a
recent, we don't know exactly how recent, many millions and even
billions of years, but a recent event which has covered up the southern
region of Enceladus and that has stretched the surface so that it's
broken to form these fissures, which we see as tiger stripes. The color
of those features is a bluish hue, and that bluish hue says that the ice
that's in the fissures, in those tiger stripes, that the ice there is
relatively young and may be fresh, at least geologically fresh. So with
this information, there is geologic evidence of recent resurfacing and
splitting of the icy surface of Enceladus.

Beyond that picture information, if you go to the next slide, when you
look at even closer views you can see on these views that there are
cracks and fissures that extend in one direction and then others that
extend in another direction, and in some places in the picture they
cross each other. This is a typical indication of multiple stages of
geology active on the surface. You can see that some of the fissures cut
across humps on the surface and this means that things occurred one
after another that were spreading or an extension along one direction
and a later extension along another direction. The more recent geologic
events cut the older geologic structure, and you could see a boundary
around the bottom third of the image where some of the older features
that are vertical in the picture, that look like parallel tracks, end at
a big boundary.

So, a geologic interpretation of that is that earlier in the history of
Enceladus those vertical cracks extended all the way to the top of the
picture, but later something smoothed them out, potentially a flow of
lava across the surface of Enceladus, to erase those preexisting cracks
and leave a new clean area, which now we see has also been cracked
itself, so that there are stages of fissures and overflow and more
fissures being formed. The geology is very interesting.

Let's go to the next slide, which shows a red line around the south pole
of Enceladus. This is a picture that shows a whole region of Enceladus
that looks relatively young, the evidence is these young features have a
slightly different color than the rest of the moon, a little bit more of
a bluish hue, and evidence for boundaries that are indicated by those
red lines. So a simple geologic interpretation would be that there have
been volcanic flows, some were near the south pole, that had erased the
craters, that are only visible outside, now, of that red line. Next
slide.

Another close-up of those tiger stripes, and you can see the tortuous
geology on the surface of Enceladus here, where multiple, the fact that
we see ridges and troughs cutting other ridges and troughs seems to
indicate, not just a single episode but multiple episodes of twisting
and turning of the crust of Enceladus. Now, on the earth we see these
same sort of features in the \... range in the U.S. Southwest, we see
these sorts of features near volcanic rifts like in East Africa, and
they're all evidence of internal activity on the earth.

On the earth we have radioactivity heating the interior of the earth,
which melts the rock, warm rock rises and these flows of rock capture
some of the solid rock on the surface and drag it along, cracking it and
breaking it and pushing it up against other pieces of earth rock. So,
you can imagine a similar thing happening on Enceladus, where the
interior is warmed by some process, fluid motions move the interior,
which take along the icy surface, cracking and breaking, and potentially
where those cracks occur there could be volcanic eruptions or events
that we see in the earth at Yellowstone or, for example, in Hawaii at
Mauna Kea, so that potentially Enceladus is evidencing the same sort of
active geology and volcanic or geothermal activity that we might see on
the earth.

Now, Enceladus is made of ice, and the temperature of Enceladus, 80
degrees above absolute zero, ice is a really good rock, and for the most
part it's completely solid, and competent, every bit as good as granite
or marble, except like on the earth you can melt that rock and then you
would have some sort of volcanic activity, and we think that ice is
acting like rock on earth, melted underneath the surface and emerging
like molten rock or like water through vents and geysers in Yellowstone
Park.

If we go to the next slide, this shows a close up of one part of that
Cassini picture, and here you can see small boulders in the insert,
small boulders with the line on the surface. It really looks like
something has happened there, those boulders are a remarkably youthful
feature and show that there's some sort of activity or some sort of
phenomenon going on, on the surface of Enceladus that is very recent and
might, from these pictures, even be something that's happening at the
time that we are looking at now, the spread in time.

The next slide shows just a close up here, and you can see some of the
structures, where the surface of Enceladus has been stretched and broken
and small icy boulders lie on that surface and pits as well.

Let's go to the next slide, which is a continuation of our story. So
just to repeat here, from Voyager we knew that some of this was very
bright and had regions that were youthful, without craters. From the
first Enceladus fly-by in February, we knew that it might have an
atmosphere that was disrupting the magnetic field near Enceladus, and so
the close-up pictures from July showed very youthful geologic features
and geology that was consistent with a much more active surface than we
might have imagined. At the same time, on that July 14^th^ fly-by, the
composite infrared spectrometer called CIRS made measurements of
radiation from Enceladus that allowed us to measure the temperature on
July 14^th^, and now we're looking at that with two color photographs,
one on the left called Predicted Temperatures, and one on the right
called Observed Temperatures.

The predicted temperature for Enceladus would be a very smooth
temperature, with the hottest, the reddest shown in these colors up near
a point where the sun is directly overhead, and the hottest temperatures
we might expect on Enceladus are about 80 degrees above absolute zero,
about the same temperature as liquid nitrogen. Instead, two things are
different in the observed temperature. First, the peak is at the south
pole, and that's where the sun isn't really shining. If you look at the
predicted temperatures, they go black there because there's no sunlight
falling there, it should be very cold. The second thing is the actual
observed temperatures are up to 90 degrees Kelvin, ten or more degrees
above the warmest temperatures predicted anywhere on Enceladus.

Let's go to the next slide. The Composite Infrared Spectrometer, CIRS,
has the capability to make some very primitive pictures, and overlaid on
this imaging picture, one of the Tiger stripes, is their single line of
detectors, a one dimensional picture, and these red and yellow squares
show the places where the spectrometer was able to measure the
temperature. You can see that the temperature they measure peaks at
about 90 degrees right on top of one of these fissures, so the fissure
is exceptionally warm, Enceladus is exceptionally warm and it's
exceptionally warm in the south polar region, and when we look at that
region in the infrared we're able to measure temperatures that are well
in excess of what the sun could cause, and particularly the highest
temperatures are right where these fissures are.

Now, there's another way to measure temperature that the instrument also
used, where they can expand their capability to look for regions that
are smaller than they can see that might have a higher temperature, and
looking at those so-called color temperatures, they're able to measure a
temperature of 140 degrees Kelvin at these locations along the tiger
stripe fissure in the picture here. So, that still may be an
underestimate of the real physical temperatures; if we were to land an
astronaut there who had a thermometer to stick in the surface, but those
temperatures are well in excess of anything that could be caused by
sunlight or any sort of greenhouse effect \...

Let's go to the next slide. So in addition to the infrared spectrometer,
the UV spectrometer watched a star as it set behind the moon Enceladus,
and this was sort of an indirect but a very sensitive way to detect an
atmosphere, because if there's any atmosphere around the moon that will
remove starlight, which is immediately detectable to our experimenting,
in fact, we measured the light from the star 500 times a second, looking
for light removal, and this next slide you see here is called "UVIS
Stellar Occulation" and it shows the path of the star behind Enceladus,
and it shows clearly the star dimming as it approached the surface of
Enceladus. So, this is an obvious indication that there's an atmosphere
around Enceladus.

The most interesting thing about this, let's go to the next slide, you
can see the exact location of our star occultation, if you had been
sitting on the spacecraft where the star would have appeared relative to
the bright edge of Enceladus. Next slide.

Both going in and going out. If we go to the slide that now says, "A &
B," if we can compare the star that was observed by us in July with the
star in February, and you can see in the star setting in July there's a
definite loss of light from the star dimming, which was not seen at all
in February. In February there's a sharp cut-off in the light consistent
with the hard limb of Enceladus, consistent with the star just blinking
off as it went behind the solid surface of Enceladus, whereas in July
there's evidence of a slower decline, which shows us that Enceladus had
an atmosphere at that time.

Now, the comparison of the star set and the star rise in July showed
that there was no similar dimming as the star emerged from the dark side
of Enceladus, and so what we're seeing is not something that varies in
time, but probably an atmosphere that is variable in space, it's not
uniform around the whole moon Enceladus. So the way to explain these
star occultations is there's just a patch of atmosphere very much near
the south pole, and you can see the artist has indicated that here in
that fuzzy area below the moon Enceladus. In July the star passed behind
that cloud and we were able to see that pinkish decrease in sunlight,
and in February we had not crossed behind that particular hypothesized
cloud, so we didn't see the diminution of star light.

So the results from the Ultraviolet Imaging Spectrograph, next slide,
are that there's a clear indication of the signal loss, attenuation of
the signal, a dimming of the star in the approach to Enceladus, the
ingress, and during the (egress) there's not any indication of the
atmosphere, and a change in star light is just a result of the
instrument warming up again after being hidden from the star by the
moon. The altitude of the atmosphere that we see is around 155
kilometers.

On the next slide we see a slightly different part of the results from
the Ultraviolet Imaging Spectrograph. In addition to the photometer,
which measures the brightness of the star, we're also able to measure
the spectrum of the star, that is, break the light from the star down
into its component colors. On the bottom of this are numbers: 1,200,
1,400, 1,600, 1,800; those are the wavelengths of light in angstroms.
All of this light, 1,200 to 1,800 angstroms, in fact, all the light the
UV spectrometer analyzes, is invisible to the human eye, so this light
would not have been visible to a human on the spacecraft and it is also
not visible to the cameras on the spacecraft. But by looking at the
spectroscopy, we're able to match the observations with the absorption
spectrum of water vapor, and what you can see here is that the red line
on the graph is a model of water vapor in the atmosphere of Enceladus,
and we can absolutely identify its signature here in the spectrum of the
star. So the light from the star that's missing is exactly at the places
where water absorbs. So not only are we able to identify water, but
we're able to determine how much water there is in that atmosphere. It's
a small amount, it would be a very, very thin atmosphere, it would be an
atmosphere that we would really call a vacuum, we wouldn't be able to
breathe in there, we don't want to breathe water anyway. We don't see
any oxygen, nor do we see hydrogen in there, which looks like just a
vent, a jet of water coming out of one of those fissures that happened
to be between us and the star that we were watching.

If you go to the next slide, we have on this slide the location of the
spectral features of carbon monoxide. Carbon monoxide could also be
identified by removing light from the star at its particular absorbing
wavelengths, but we don't see any here that allows us to set an upper
limit of only a few percent of the water is being accompanied by carbon
monoxide. This is important, because I'm going to talk in just a second
about the results of another Cassini experiment, the ion and neutral
mass spectrometer, which was able to detect not only the water we saw
but other constituents in the atmosphere, but its detection is of a
different sort, all it's able to detect is the mass of the molecule that
is in the atmosphere.

So they detected mass 18, which is H2O, and they detected mass 28, which
is a little bit of a mystery, not that there aren't molecules with an
atomic mass of 28, a molecular mass of 28 and atomic mass units, but
there are two at least that were of interest. One could be two molecules
of nitrogen at 14 each; another could be a molecule of carbon monoxide
at 12 for carbon plus 16 for oxygen. What our results show is it's very
unlikely that they saw carbon monoxide, so that the likely measurement
of the neutral mass spectrometer can now be interpreted, in light of the
ultraviolet results, to show some significant fraction of nitrogen
molecules that are also accompanying the water escaping from the surface
of Enceladus.

Let's go to the next slide. This is from a graph on the ion neutral mass
spectrometer, and it shows the density of water molecules with altitude.
There's also a purple line there, which is a computer model, and all
that a person can say is that computer model is not very successful
explaining the blue and red measurements. So what that means is our
models of what's happening on the surface of Enceladus are still
incomplete, but this does show the definite phenomenon that water is
much more abundant near the surface of Enceladus; and secondly, that at
two different places where the spacecraft approached Enceladus and just
a little later where it exit, there are big variations in the amount of
water. The blue and the red dots are not on top of each other, in fact,
they're different by some large factors, maybe a factor of ten from
place to place.

This says, once again, like the UVIS results from the ultraviolet star
occultation, that the atmosphere of Enceladus is really not uniform,
it's really varying from place to place strongly by maybe a factor of
ten, and this says that the atmosphere is the wrong thing to talk about.
Many of us have been talking about these eruptions on Enceladus as being
like a vent eruption, like a geyser, like a jet from a comet, and those
are in one place and not on another, so if you happen to fly through one
and you see a big measurement of water vapor or if a star happens to
pass behind one of those jets but if it doesn't go near the vent then
you see something really different, and that explains why three of the
four star occultation cuts, two approach and two going away from
Enceladus in February and July, of all of those four only one actually
shows the presence of water vapor.

Let's go to the next slide, which is a slide showing the mass spectrum
below 500 kilometers altitude, and what you want to see here is you can
look and see that there's a big peak at mass 18, which is water, and
there's another big peak at mass 28, which is most likely nitrogen
molecules.

Let's go to the next slide. I've mentioned so far the magnetometer
results, the camera results, the infrared spectrometer results, the
ultraviolet spectrometer results, the ion and neutral mass spectrometer
results, all showing an indication of a very confined and very sharp
presence of water near Enceladus. In fact, because of the lack of
hydrogen and oxygen, probably water that was just freshly released from
the surface and hasn't had a time to be broken down by sunlight into its
atomic constituents, and in addition to that, there were also direct
measurements made by the cosmic dust analyzer, a small instrument on the
spacecraft that measures dust particle small grains near and distant
from Saturn.

What they see in this slide that I'm showing; their high-rate detector
detects an abundance of small grains near Enceladus. Now, that's very
exciting, but the more exciting thing is that those grains are not
symmetric about the moon, in fact, they seem to be coming from some
place very near the south pole, which is exactly where the spectrometers
are seeing evidence of current activity, current eruptions on Enceladus.
So the cosmic dust measurements, the direct measurements of dust near
Enceladus also show some evidence for eruption, and the idea would be,
like on a comet, as the gases are shot out from the comet vent or a jet
on the comet, they also carry small grains of ice, and as the jet moves
away from the comet, the gas and the ice separate a little bit. And it's
seen here that the maximum of dust is some 25 seconds later than the
maximum of water that was seen by the neutral mass spectrometer both on
the Cassini spacecraft as it flew by Enceladus, so near closest
approach, but not exactly at closest approach. The amount of water vapor
there at the spacecraft and the amount of dust peaked at the different
points, so this is saying to us that we have a very complicated and
unsymmetric source of water and dust near the south pole of Enceladus,
most likely associated with geologic activity, where water vapor and
associated molecules of nitrogen and grains of ice are being shot out of
a fissure, what the camera team called the "tiger stripes." Next slide.

This slide shows how we can distinguish where those dust particles are
coming from, and the blue curves are offset from the curves that show
the very symmetric prediction if even the Southern Hemisphere was the
whole source. So we're seeing a source of dust that's shown in this
model to be much, much smaller and much more localized than the whole
Southern Hemisphere, and maybe only a few percent of the surface, maybe
just one or more of those tiger stripes is actually now emitting gas and
dust. We flew by Halley's Comet and we saw jets of dust turn on and turn
off, and so that may be the same sort of thing that's happening on
Enceladus. Next slide.

Looking again at the picture of Enceladus, it's quite possible that each
of these tiger stripes, or some fraction of them, is an erupted vent,
something like a geyser occurring on Enceladus. It may not occur all the
time in that the geologic activity associated with those eruptions is
what's made the surface of Enceladus appear so young near the south
pole.

We go to the next slide, and you may ask, how could we possibly explain
this? One possible explanation is that there's some sort of heat in the
interior of Enceladus, and the picture we're looking at now is an
idealized model of a block of the surface of Enceladus with that blue
feature along the top, that prismatic feature is meant to represent one
of the tiger stripes. So we see there's a tiger stripe, which is a hole
in the surface of Enceladus and underneath that hole there's some source
of heat, we don't know if it's from radioactive materials or if it's
from tide stretching of Io by Jupiter is what's the source of volcanic
activity on the moon Io.

In a similar way, there may be some sort of stretching and pulling of
the interior of the moon Enceladus to produce heat. But there's a
challenge with that, as Enceladus is very small, and there doesn't seem
to be any particularly strong tides \... on it, and in fact if Enceladus
does have a source of heat, why is it that the other satellites, the
other small satellites near Saturn, and even bigger satellites of Tethys
and Rhea do not have a similar sort of heat and a similar sort of
eruption, like we see around Enceladus. That's an unanswered question.
But there are two things I want to draw your attention to on this
figure. One is the idea of a slurry. There's actually the possibility of
an antifreeze in the water that's underneath the surface of Enceladus,
and a good antifreeze would be ammonia. So if we mix ammonia with water
we can make sort of a \... that will not freeze until about 100 degrees
Centigrade below zero, or a temperature of 170 degrees Kelvin.

So, this gives us the possibility, this antifreeze gives us the
possibility of using less heat and still making some liquid water
underneath the surface, which then would be under pressure and could
potentially escape through a vent in the surface. At the top you can see
little arrows showing the evaporating H2O molecules, and those are the
ones that were seen by the ultraviolet spectrometer and by the neutral
mass spectrometer. So, what's really been seen is what's at the top,
those little arrow heads, and everything below that is an inference of a
possibility and maybe not one that's generally agreed to, but one
possibility of explaining the source of this eruptive activity on
Enceladus. Next slide.

Here's a summary slide. If you click on that you can see that the
imaging system has shown a young, warm south pole. Click again, you can
see that there's a tenuous polar atmosphere, which is shown by the
ultraviolet spectrometer and neutral mass spectrometer, and the
magnetometer field draping. There's a non-uniform distribution of
particles, grains of ice that have been seen by the CDA. So the whole
story together is a story for eruptions, venting of gases, particularly
water vapor, sort of water style active geology that parallels the rocks
melting and releasing water here in a geothermal system on the earth,
and the puzzle that this leaves us is how such a tiny little satellite,
only 300 miles across, could continue to be warm and active and giving
us a spectacular showing after 4.5 billion years.

The next slide just summarized the results from my experiment, that the
occultation of the star Belatrix Gamma Orionis on July 14^th^ determined
the composition of the Enceladus atmosphere, it's water vapor with
limited amounts of carbon monoxide, perhaps some nitrogen in there. It
also said that the Enceladus atmosphere is very localized, and the
picture we have in mind is of jets of gases and grains of ice shooting
off under the fissures on the surface, and we've done preliminary
calculations of the amount of water vapor escaping, and that amount is
sufficient to supply the atomic oxygen in the Saturn system that was
detected by the UVIS, and also to re-supply Saturn's E-Ring, so that
potentially these eruptions of water and ice from the surface of
Enceladus are making Saturn's E-Ring and also making the cloud of oxygen
that was discovered just last year by Cassini.

That concludes my presentation. In summary, we're potentially solving
some of the mysteries of Enceladus, if it has geologic activity,
including hydrothermal vents and geysers. And that would explain why the
surface is young and so bright and shiny, and the material that's
escaping from Enceladus in these vents is enough to make the cloud of
oxygen that was discovered by Cassini, and also to make the particles
that form the very, very tenuous E-Rings around Saturn.

This is the conclusion of my presentation. I'm open to your responses
and I thank you for your attention. Good-bye. Hello, I didn't really
sign off, I am able to take questions now if people have them.

Ron Larry, can you hear me?

Dr. Esposito Yes. Go ahead.

Ron This is Ron Hobbs. I'm a solar system ambassador. Do you know if any
data came from this fly-by that gives any evidence of Enceladus being
differentiated? One would imagine if it was warm if there's something
\... that all the heavy stuff would have gone down to the center, is
there any evidence of that?

Dr. Esposito Not that I've heard yet.

Ron Thank you.

Rachel Larry, this is Rachel Mann from the Solar System at Decatur. My
question to you is based upon all this evidence that you recently found
from the fly-by, are there other plans to do more fly-bys of the moon?

Dr. Esposito Well, that's a very good question. You know the reason we
did this fly-by was because of the discoveries we made in February, and
I think it's a very natural thing for the Project Science Group to
consider changes to our current plan to have other close fly-bys of
Enceladus, and that's really what we need to sort out this very
complicated structure here.

Rachel Thank you.

Dr. Esposito You're welcome.

Steve Larry, this is Steve Lee. I'm at the Denver Museum of Nature and
Science.

Dr. Esposito I know you, Steve. Go ahead.

Steve I'm still a little confused about the energy source to actually
produce the melting on Enceladus. I thought there wasn't a strong
orbital or tidal resonance for Enceladus right now, and \...

Dr. Esposito That is true. Yes.

Steve \... evidence that the orbital changes would support a stronger
resonance in the past, or how does that work?

Dr. Esposito Your question is a good one, in that the tides, there's no
theory that would give the tidal heating that's sufficient to melt the
interior of Enceladus, and there's no reason to expect at this present
moment that tidal heating is sufficient, and we were guessing that if
tides were raised inside Enceladus they could melt it. It's possible
that there was a situation in the past where there could have been more
tidal excitement, I don't know any good evidence for that. There's also
the possibility that Enceladus might have been spinning much more
rapidly early on and when it was slowed down to its current rate, where
one side always faces Saturn, just like one side of the earth's moon
also faces the earth, when it was slowed down to that synchronous
rotation that energy was released, which is now stored and could do the
work to melt that water. But, there is no good explanation right now of
how the interior could melt to create the eruptions that we've seen.
Nonetheless, we see water vapor, which would not melt at the temperature
of Enceladus, and CIRS, the infrared spectrometer, sees a surface that
is much warmer than can be explained by sunlight.

Steve I guess the theorists need to catch up with the observations now.

Dr. Esposito That's a particular advantage of space missions, that we
provide material which really needs to be explained, and just as you
said, the explanation is not clear at this moment.

Steve Thanks.

Alan Larry, this is Alan Davenport up at the University of Maine, at the
\... planetarium here. I want to thank you, first, for taking the time
to be with us. This is fantastic. I was wondering if any information or
data from your study so far of Enceladus would allow you to say that it
did or did not possibly form as a K.B.O. from much further out. Is there
any signature or compositional information that enables you to establish
its origin?

Dr. Esposito It doesn't appear distinctly different from other Saturn
satellites except it's brighter and has more water visible on the
surface, so, that's certainly consistent with it being a captured Kuiper
Belt Object. But it's hard to imagine an object wandering in from the
Kuiper and ending up so close to Saturn within four radii of Saturn and
in such a regular equatorial, uninclined, low eccentricity orbit. So it
certainly has characteristics which remind one of a Kuiper Belt Object,
and it's not impossible, it's just a very improbable event that an
object could have come from so far away and end up right in the middle
of the Saturn moon family.

Alan I understand. Thank you very much.

Rachel Larry, this is Rachel again. Just out of curiosity, has this all
hit the newspapers and the science magazines yet?

Dr. Esposito No.

Rachel Okay.

Dr. Esposito Let me say that a little more clearly, because you know on
this telecon we can't talk about things that haven't been released yet.
But this morning in London there was a press conference associated with
the PSG, so just this morning some of the more recent information, that
is about the composition of the material coming off of Enceladus and
about the fact that there's sufficient material to actually explain the
existence of the E-Ring and to produce all the oxygen we see in the
Cassini discovered ring. These have just been released today, so you
probably won't see them in the paper until tomorrow.

Rachel Okay. Thank you.

Mike Doctor, this is Mike Lipkus, solar system ambassador. \...
reference the cloud activity around the southern pole and \... break
down that \... Are you suggesting that \...is with the E-Ring?

Dr. Esposito I'm sorry. I didn't catch the question. Could you repeat a
little closer to the mike?

Mike Yes, is there a suggestion that Enceladus is evaporating into the
E-Ring?

Dr. Esposito Right. Not all of Enceladus, but the amount of material
that's needed to produce the E-Ring against the losses due to grinding
by meteorites and erosion by the plasma in the Van Allen belts of
Saturn, the amount that's needed is about a kilogram per second. The
amount of dust that's coming out of the vent on Enceladus, if it
represents just a few percent of the water that we see, and it's also
water, it would just be water ice, so just a few percent of the water
that we see is ten kilograms per second. So the amount of material
that's coming out of Enceladus is enough to create and replenish the
E-Ring, and to replenish a ring might seem like a lot, but remember this
is the E-Ring, which has just barely been seen by Cassini, so we're not
talking about making the main rings of Saturn by grinding up or
evaporating Enceladus, but we're talking about making one of the very
tenuous rings that's centered on Enceladus from dust, grains of ice that
are blown out of these vents.

Mike This is a very bizarre place.

Dr. Esposito Yes. Well, nobody could really have predicted this, and as
I was explaining to Dr. Lee, this is one of the reasons that you have to
go there, being there is much better than any sort of theorizing or
modeling we can do before the event.

Mike Absolutely fascinating. Thank you.

Dr. Esposito Are there other questions?

Steve Larry, this is Steve Lee again. You talked about the possibility
of future alterations to the mission, how likely do you think that's
going to be to get some more really close fly-bys where you could
examine these possible eruptions?

Dr. Esposito I can't say, because the people who are making that
decision are meeting Thursday in London. But in teleconferences that
we've had, in the past few weeks there's been significant support for
changing the mission and there's likely to be some valid resistance to
that because it may cost more fuel and it may cause people to re-work
some of the plans that they have already. So, I think that is going to
come out of a meeting that's still going to be held in a few days, and I
believe even if we don't re-program the mission to look at Enceladus
more closely during the nominal mission during the next few years, it's
possible that the mission would be extended, and in such a mission that
would be one of the major objectives, that the actual orbit of the
spacecraft would be designed to encounter Enceladus multiple times. We
still have that all open in the extended mission and at the moment we
have fuel and electrical power and all the other resources, so that the
mission could be extended two or four years.

Steve That's great. Thanks.

Dr. Esposito If there are no more questions, I thank you again for your
attention. Good luck to any dissemination of these very interesting
Cassini-Huygens results. Thank you again and good-bye.

W Thanks, Larry.

W Thank you very much.