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

FTS-NASA-VOICE

Moderator: Trina Ray

June 24, 2008

1:00 pm CT

Coordinator: Excuse me. I'd like to remind all parties today's call is
now being recorded. If you have any objections you may disconnect at
this time. You may begin.

Jane Jones: Hello everyone and welcome to the fourth anniversary Charm
Telecon. We've been doing these telecons now through the whole prime
mission and this is kind of the wrap up of the prime - Part 1 of the
wrap up. My name is Jane Houston Jones. I'm with Cassini Outreach and
I'll be your moderator today.

We have three speakers today. Dr. Linda Spilker who is our Deputy
Scientist here on the Cassini mission. She's been on Cassini since 1988
and before that she was on the Voyager mission for 13 years. So she has
a lot of wonderful experiences here on planetary missions at JPL. Our
two speakers after Linda does an introduction are Dr. Andy Ingersoll
from Caltech. He's in the - he's a professor of planetary sciences and a
member of the imaging team - the Cassini Imaging Team.

Also joining us today is Elizabeth Turtle and she goes by the name Zibi.
And she's at APL, the Applied Physics Lab at John Hopkins University and
is also on the imaging team. So what I'm going to do is remind everyone
if you do ask questions to say your name before you ask the question so
that the talk can be recorded - so that your name will be recorded.

And if you need to make noise or anything you can mute your phone.
Hopefully most of you can mute your phone by pressing star, 6. And those
of you who can't, that's fine too. With that I'm going to turn it over
Linda.

Linda Spilker: Okay. Thank you very much, Jane. This is a very special
anniversary for Cassini - its four-year anniversary. It's the end of
what we call our prime mission and the completion of something like 76
orbits around Saturn including 45 Titan flybys and a host of close
flybys of (IT) satellites.

And you'll be hearing - I have an echo.

Jane Jones: Linda, are you on a speakerphone or did you pick up\...?

Linda Spilker: No I picked it up. I'll go ahead in spite of the echo.
Yeah, 45 Titan flybys and a host of IT satellite flybys. If you go to
the slide Huygens and Cassini, the scientists and the machine, the
mission was named after two scientists. The first was Christian Huygens
and he was a Dutch scientist who actually discovered Titan; so it's
quite appropriate that the Huygens Titan mission would be named after
him.

And as well, he discovered the true nature of Saturn's rings that
Galileo initially saw what he thought were two large moons on either
side of Saturn and then they disappeared for a while and then they came
back. And it was Huygens who determined that they were actually rings
around Saturn.

Giovanni Domenico Cassini was an Italian-French astronomer and he was
the one who discovered a gap between two of Cassini's rings, the A and
the B ring; named the Cassini division in his honor. And he also
discovered several of Saturn's satellites including Iapetus, Rhea,
Tethys and Dione. On Page 4 are photographs of the Cassini orbiter and
the Huygens probe.

And to give you an idea of just how large the spacecraft is you can see
on around the bottom of the Cassini orbiter you can see little figures
of their people dressed up in special suits for working on the
spacecraft to give you an idea of just how big the entire spacecraft is.
And that gold covered object is the Huygens probe and it's shown without
its thermal blankets on the right hand side of the page.

Going on to Page 5, the Cassini spacecraft - you can see it is indeed a
very large spacecraft. It's 22 feet tall. That high-gain antenna, the
white antenna at the top, has a diameter of 13 feet and the spacecraft
itself has a mass of about 2.8 tons. And if you include the fuel for the
spacecraft as well as the Huygens probe then you're looking at something
like a 6-ton spacecraft and the sheer size of Cassini helps explain why
we didn't take the direct route to Saturn but instead had two flybys of
Venus, a close flyby of Earth and then of Jupiter to give us the
additional gravitational assist to go on out to Saturn.

The power of Cassini at Saturn orbit insertion, that's the time on July
1, 2004 we first arrived, was about 700 watts and Cassini is powered by
three radio isotope thermoelectric generators shown on the diagram. And
the plutonium power source that we use the heat plume from the plutonium
decay to power the entire spacecraft. And that is slowly decreasing with
time so we have a little bit less power every year as the mission has
gone on. Yes?

Matthew Ota: (Unintelligible) question.

Linda Spilker: Yes. What's the question?

Matthew Ota: This is Matthew Ota with the Saturn Observation Campaign.
I'm just curious as the amount of propellant left for the main engines.
The 490-newton engines (unintelligible) insertion in.

Linda Spilker: Right. Yeah - right. I'm not sure of the exact number
although I know that we burned - we have certainly used over half of our
fuel and a great deal of that was used just to go into orbit around
Saturn. So I don't have an exact number for you though.

Matthew Ota: Okay. Thank you.

Jane Jones: But those facts will be part of the super-duper cool facts
in next month's Charm Telecon which will be Part 2 of this fourth year
anniversary. We're collecting all those metrics for (the next)\...

Andy Ingersoll: And in - Andy Ingersoll. And in practical terms we can
go on for another ten years with the fuel we've got.

Linda Spilker: Right. Right. Right. Yes, we tend to use the fuel
primarily for trajectory correction maneuvers when we are in close to
Titan or various targets and then we have reaction wheels that we use to
actually turn the spacecraft. So that makes it a much less fuel
intensive mission to say something like compared to the Voyager mission.

Let\'s see for the spacecraft we have a .5 Gigabit recorder and the
Huygens probe by itself weighed about 700 pounds. And the Huygens probe
is what we sent into the atmosphere of Titan and by parachutes it
dropped down to the surface and sent back data about the atmosphere and
pictures including great images once it landed on the surface.

Onboard Cassini we have a set of 12 scientific instruments including -
they're sort of in three groups­. The Optical Remote Sensing instruments,
which measure from the ultraviolet into the far infrared. We have some
Microwave Remote Sensing instruments including a radar instrument. And
we actually use the high-gain antenna for radio science experiments. And
then there's a suite of magnetospheric and plasma instruments including
a dust analyzer, an instrument that measures the magnetic field and
additional instruments that measure electrons, protons and ions in the
Saturn system.

Moving on to Page 6, if you look at the bottom of Page 6, there are
little asterisks with the instrument names indicating each of the places
where the instruments are - the various instruments are commanded or the
instrument operations are run from these locations. So you can see that
we have 10 of the instruments from the United States and two of those
whose activities are run one in England and one in Germany.

Moving on to Page 7, Cassini is truly an international mission and this
is represented by the 17 flags that are shown here surrounding Cassini.
These various countries provided not only scientists - there's about 250
scientists on Cassini but also engineers and various pieces of the
spacecraft or the instruments that were built in countries around the
world.

About 1/3 of the Cassini scientists are international scientists and the
other 2/3 are US scientists. Moving on to Page 8, the cost of Cassini -
the total cost is about \$3 billion and that's spread between NASA,
about \$2.5 billion for NASA and about \$0.5 billion for Huygens. And if
you spread that over the roughly - not quite 20 years of the mission,
that's about \$150 million per year although the current operating costs
for Cassini, since we're just in the operation space and aren\'t
building the space craft, are about \$80 million per year.

To put things in perspective, the Cassini budget is roughly half a
percent of the NASA annual budget. And to further put that in
perspective, the NASA annual budget is about 1.7% of the US
discretionary spending or about .6% of the US budget. So you can sort of
do the math and see that of the total US budget Cassini is really a very
small part of that.

Moving on to Page 9, just to give you an idea about the Saturn system
and how huge it is, what's shown here is the planet Saturn and its rings
plus the Earth and the moon; each of them shown to scale. And the
distance between the Earth and the moon is to scale as well. So you can
see that this is indeed an immense system and Andy will be talking more
about the planet itself in his discussions.

But you can see that the Saturn plus the rings would just fit in between
the Earth and the moon and it certainly dwarfs the Earth. Moving on to
Page 10, this is again continuing just an overview of the Saturnian
system. So far we've discovered between ground base and also Cassini
we're now up to a count of about 60 moons around Saturn and they come in
all different shapes and sizes.

Titan is the largest of those. It could be a planet in its own right had
it formed elsewhere in the solar system. And it has a thick nitrogen
atmosphere with methane and other hydrocarbons in it and it'll be
something that'll be discussed in more detail at the Charm Telecon in
July. And as you can see the tiny satellites, the ones closest to
Saturn, are toward the left and you can see that they come in irregular
shapes; they aren't necessarily spherical balls.

They might indeed be fragments left over from the break up of perhaps
larger objects and then as the moons get larger you can see that they
become more spherical in shape although Hyperion and Phoebe both have
irregular shapes as well. In the bottom panel it shows the ring system.
The rings have very simple names; basically just A through G, and they
were named in their order of discovery.

And it also shows, with the gold colored arrows, the locations that
various spacecraft have flown through the Saturn system including
Pioneer 11 and Voyager 1 and 2 and then Cassini, which flew through the
system at the closest point between the rings. One of the rings of note
is the E ring. We now know that Enceladus is indeed the source of that
ring that there are jets of material coming out of the south pole and
Zibi Turtle will talk about that in more detail in this telecon.

Going on to Page 11, well, what did the tour look like - this fourth
year of the tour? What the goal in the final year was to basically go up
to very high inclinations - in fact the very highest inclination that we
have of the mission to date. There are roughly 27 orbits in this fourth
year of the mission; that was roughly 10 sequences that we had to send
up to Cassini.

It included 13 targeted flybys and 7 non-targeted flybys where we just
picked non-targeted distance of about 120,000 kilometers or less. In the
fourth year of the tour we started Cassini in a set of equatorial orbits
and those are a good opportunity to get IC Satellite flybys and
including one of Iapetus that we flew very close to in September of 2007
and got back some remarkable data about this very interesting moon with
one side as white as snow and one side as dark as charcoal and I'm sure
that Zibi will have a lot of highlights from that flyby.

We also had two very low non-targeted flybys, one of Rhea in August and
one of Epimetheus, which is one of two cool orbital satellites in
December of 2007. And then we had our last targeted Enceladus flyby of
the prime mission and that was in March of this year and it was the
closest we had yet come to this object and we got some really incredible
data.

We actually flew through the jets and plumes of material and we were
able to do in situ sampling and I'm sure that Zibi will talk more about
that as well. Well then we spent most of the fourth year after the
Iapetus flyby increasing the inclination and we're now at an inclination
of over 70 degrees and that's a wonderful opportunity to look down at
the north and south poles of the planet, the rings open up like a giant
bullseye.

And it's also a good time for in situ sampling especially in the regions
over the poles, what we call the open field line region - the region
through which the aurora are generated to understand more about Saturn's
auroral processes. So this is a really a very exciting and a very new
time in the sense that we're getting to see Saturn in a way that no one
has seen it before from these very high inclinations.

And also we've begun work on our two-year extended mission. We're in the
process of putting those sequences together because obviously it starts
on July 1 of this year. And then also are looking ahead to what we call
an extended-extended mission, which would be in the period after what
we're calling the Cassini Equinox mission or the first extended mission.
And we're hoping that perhaps we might be able to go as long as even
seven years all the way to the solstice for Saturn. So that would be
very exciting indeed and those plans are in the works.

Going on to Page 12, this is just a mission summary chart. It gives you
in the box on the far right just indicates the activities in the final
year of Cassini's activity where we are talking a year now that goes
from July1 of 2007 to July1 of 2008. You can see some of the highlights
there. The targeted Iapetus flyby is indicated, the blue triangle is the
close Enceladus flyby. And you can see indicated that the inclination
profile is showing as a function of time in the tour and that we are
indeed in very high inclinations in the remaining weeks. And it'll also
be in very high inclinations for the first part of the Cassini Equinox
mission.

On Page 13, just a list of the targeted flybys including the Titan
flyby, Iapetus and Enceladus and also included in this table are the
dates where we flew by these various targets. And if you're interested
in going and looking at some of the data, the radar maps from the Titan
passes or the images associated with them, you can use these date to go
into - go from the Cassini Web page to go into and actually look at some
of the data and images that have come back from these flybys.

And with that, I'm going to turn over the discussion to Dr. Andy
Ingersoll and he will tell you about some of the highlights from the
Saturn flyby. And I believe you have to skip to I think it's Page 55...

Jane Jones: Correct.

Linda Spilker: ...in the presentation to get to Andy's material.

Andy Ingersoll: Hi there. I'll tell a few jokes or at least will stall
for time while you get to Page 55. You should see a blank white page
with except for the words Saturn's atmosphere, results from Cassini,
Andrew P. Ingersoll, June 24. And that is my topic indeed. I will sort
of end on a few remarks about Saturn's interior.

It's obviously harder when you're in an orbiter to sample or measure
anything about the interior but we hope to be able to do that. The prime
mission was not the best way to do it but there's interesting
possibilities for later on to measure Saturn's interior. Now, move on to
Page 2 and there is an early in the mission picture of Saturn and its
rings.

And the sun in this picture - you can actually tell where the sun is
from the terminator. The terminator is the boundary between day and
night on the planet. And you can see that the terminator is sort of
tipped over indicating that the sun is maybe at the 4:00 position,
treating noon as being straight up in this picture.

And there's a very curious thing about this picture. I'll give you 15
seconds to spot it. The northern hemisphere of Saturn which is peaking -
which is getting some illumination through the rings from the sun, which
is down at the 4:00 position, looks blue. And it's a different color and
we scratched our heads about that for a long time. Remember, this is an
image taken early on - probably 2004 maybe early 2005.

And the ring scientists said, "Why is the atmosphere blue?" And the
atmospheric scientists said, "Well, why is light that shines through the
rings colored blue?" And so each side was blaming the other for the blue
color and now in 2008 we have figured it out because the sun is
approaching the equinox season when it's more - in this diagram it would
be at the 3:00 position.

And the northern hemisphere is receiving direct sunlight not filtered
through the rings and at first when we saw direct sunlight it still
looked blue. And so we couldn't blame the rings for that because it
wasn't being filtered through the rings. And now that we're - that the
northern hemisphere has been baked in sunlight for a year or so it's
turning pink or whatever that color of the southern hemisphere is in
this image.

So it seems to be some kind of chemical change in the atmosphere - smog
if you like, forming the way smog forms under the action of sunlight.
And in fact it could have some of the same ingredients as smog, little
particles of soot, hydrocarbons in other words, condensing out from the
mixture of hydrocarbons that are in the gaseous hydrocarbons, which are
in the atmosphere; methane is the primary one - that's one carbon and
four hydrogens.

So somehow the sunlight is turning some of the methane into smog and
it's beginning to look that pinkish-orange-yellowish color instead of
blue. When the blue skies is just the clean atmosphere not getting very
much sunlight and when the northern hemisphere was behind the rings it
was clean. All right, let's move on and talk about electrical storms.

Lightning is a very interesting phenomenon, not even very well
understood on Earth. The only place besides Earth where we know for sure
that there is lightning is Jupiter and that is - well, we know that
because we look at the dark side of Jupiter and we see - of course we
see a dark planet but we also see these lightning storms. And Voyager
discovered the, Galileo got a very good look at them and so we said,
well, let's look for the lightning storms on Saturn with Cassini.

Next slide shows you one of the problems. This sort of double picture
shows a little storm there; it's actually not too little - it's
thousands of kilometers across. Remember Saturn's a lot bigger than the
Earth, ten times bigger. And so this is like a - it's bigger than a
hurricane on Earth - like a big winter storm on Earth and it's producing
lightning flashes and - but we can't see them.

We can hear them. We can hear them with the radio wave detector, the
RPWS - Plasma Wave Radio something or other detector on Cassini and when
this little storm comes around on the side of Saturn facing the
spacecraft, we get these radio bursts. They're very short bursts, just
like a short lightning burst and then as the storm sets every Saturn
day, it goes on to the other side of Saturn where the spacecraft can't
hear the - or can't collect the radio signals - we don't hear them.

And then it comes around again a half a Saturn day later and we get the
bursty radio signals. And the reason we haven't seen them visually even
though we do get good views of the dark side of the planet or let me
call it the night side of the planet - is that the night side of the
planet is not very dark. And the reason for that is that you've got
these enormous rings scattering light from the sun and filling the sky
from the point of view of someone floating a balloon in Saturn's
atmosphere.

So the rings fill the sky and the brightness on the night side of Saturn
is brighter than a full moon - than the Earth at night under a full
moon. Even though the sun is only 1% as bright and the sun, of course,
illuminates our full moon. The sun also illuminates Saturn's rings but
the Saturn's rings are such a much bigger portion of the sky that the
overall brightness on the ground on Saturn, if there were a ground, is
brighter than a full moon.

And so that means that it's never very dark and the lightning flashes
which sort of have to filter up through the clouds are - although we're
probably getting some light from them, they're indistinguishable from
all the little puffy clouds illuminated from above by the rings. And we
can't tell the clouds illuminated from below by lightning from the
clouds illuminated from above.

But back to this image here of this little storm. The - it's very
interesting - there's - long periods go by, up to two years, where there
is no radio waves signaling lightning. And then all of a sudden within a
day the radio waves will start up and the RPWS will pick them up and
alert the imaging team. And if we happen to be taking images - we can't
respond that fast - but if we happen to be taking images the storm -
there'll be a new storm.

So that - these storms seem to pop up within a day and emit lightning
very - as soon as they pop up. It turns out the people who are best able
to spot the storm when the radio waves start up are the amateur
astronomers here on Earth who can just go out the next night and point
their telescopes and say, yep, it wasn't there last night and it's there
tonight.

So it's been a very nice sort of coordinated effort between professional
astronomers and amateur astronomers and we're of course on the Cassini
team very grateful for their efforts. Now, the next slide, which is
entitled Saturn, electrostatic discharge's intensity, shows you sort of
the history. You'll look at the bottom; you can see the day and the year
from 2004 to 2006. And in the top panel, the black vertical lines are
when the RSPWS instrument was receiving these radio signals from the
lightning.

And you can see that there was around Days 200 and 250 in the year 2004
there was a lot of radioactivity from lightning. Then there's a long
pause and around Day 140 in 2005 there was a little whiff of lightning
and then a big storm started up in 2006. And each time - and we never
saw evidence of a storm in 2005 but there was a big storm during the
radio episodes in 2004 and 2006. And now we've got one going in 2008,
which is much longer-lived than the other two.

It's been going for six months and it's still going strong. And that's
the only source of lightning on the planet. The next slide, which is
labeled planetocentric latitude and west longitude shows a movie over
20-25 days of - I can't remember - I think this is the 2004 storm. Maybe
it's the 2006 storm actually, and it's in the false color; a combination
of three filters that are sensitive to cloud height, so the yellow are
the highest clouds.

And you can see the different active center sort of popped up suddenly
like alpha and beta and then drifts west and watch the alpha one in the
left hand column as time goes by. Time increases as you go down. Now it
started off as a high cloud, that yellow color and then it turned into,
if you follow it in the right hand column, into blue clouds. Actually
blue signifying a hole in the cloud. And we don't fully understand why
it goes from a very big high cloud into a hole in the cloud but - some
kind of rebound where the clouds evaporate.

But figuring this kind of stuff out, the first step is to gather the
information and the data and the second step is to read all the books on
Earth lightning and Earth's thunderstorms and then the final step is to
put it all together into a new view of thunderstorms and lightning and
that's what we're trying to do right now. Obviously lightning on a giant
planet is not going to be quite the same as lightning on the Earth.

It probably does involve water, probably does involve ice particles and
rain drops but there's no ocean underneath, there's no moist land. It's
just a deeper atmosphere. So the hope as with all of these kind of
studies is to understand more about the phenomenon in general - in this
case, the phenomenon is electrical activity in the atmosphere using a
more - a broader context than just studying the Earth alone.

Our next slide shows - yeah.

Trina Ray: Question. Hi, this is Trina. It looks like all the storms
sort of appear at the 300 west longitude even though after that they
drift. Did those storms earlier also appear at 300 west longitude and
does that mean anything that they're all in\...?

Andy Ingersoll: Well we wondered about that. The storms are spaced two
years apart and we wonder if maybe it's the same storm but it just sort
of went dormant for two years. Actually if you go back one slide, I
didn't talk about - this is the one entitled Saturn, electrostatic
discharge's intensity - I didn't talk about the lower panel.

But you can see the answer to your question. The 2004 storms, which are
these little black squiggles around 300 west longitude were sort of
drifting to higher longitude values; that means they were drifting to
the west. And then the - and that's the dashed line, sort of projecting
that drift rate. And then nothing happened for two years and then the
2006 storm started up at about 200 west longitude, having drifted almost
once around the planet.

And it's possible it's the same storm but we don't really know. And so
back to the next slide, it's possible that there's an active storm
center just as you were guessing and then the clouds are lofted to
higher altitudes where the winds are stronger and more easterly - in
other words, towards the west at high altitudes and then they drift
away. So that's quite a reasonable possibility.

Matthew Ota: Question. Slide 60.

Andy Ingersoll: Another question.

Matthew Ota: Yes. This is Matthew again with the Saturn Observation
Campaign. I'm looking at Slide 60. I have a pretty fundamental question.
How do scientists determine where the prime meridian and how they
determine where the prime meridian is on Saturn's atmosphere since it's
not a fixed land...

((Crosstalk))

Andy Ingersoll: No. I understand the question.

Matthew Ota: Okay.

Andy Ingersoll: You don't have a solid planet so you can't just decide
that Greenwich is the prime meridian the way we can on Earth. Well,
that's a big problem and it's still an unanswered question. I have some
remarks on that at the end. With the other three giant planets, the
magnetic field of the planet is tipped relative to the rotation axis of
the planet. And so like a wobbling top, all the phenomena that are
associated with the magnetic field, all the charged particles, all the
radiation belts wobble once a day.

That's true of Jupiter, Uranus and Neptune and that wobble is detectable
from Earth, in the case of Jupiter, and very clear, detectable from
spacecraft. And so we define the internal rotation of the planet from
the magnetic field since the magnetic field is generated inside the
planet. And so that becomes our reference frame and that substitutes for
a solid planet and that defines our prime meridian.

And then it's just an arbitrary decision, sort of as it was on Earth,
once you know your reference frame you just pick some place to be the
prime meridian and on Earth there was a little bit of politicking going
on between Paris and Greenwich but for some reason the English won. And
so on Saturn there's no such politicking but there is a prime meridian.

Unfortunately - oh and on Jupiter there is a prime meridian and Uranus
and Neptune too. Unfortunately for Saturn, however, the magnetic field
is not tipped and so there is no wobble and therefore although we can
see things moving in the atmosphere we can't decide what reference frame
to use to measure the wind. And there are electrical currents outside
the planet and those generate magnetic fields but they don't come from
inside the planet.

And so we thought after Voyager that we had measured the internal
magnetic field and had detected some - a wobble or a tilt or anomaly or
something and it turns out we were detecting external fields instead and
that period has changed over the years and there's no way the inside of
the planet could change its rotation. So we really don't have a
reference frame for Saturn.

Matthew Ota: Okay. Thank you...

((Crosstalk))

Andy Ingersoll: Yeah and I'll talk more about how we hope to get it.

Matthew Ota: All right. Thanks very much.

Andy Ingersoll: Okay. Now there's a picture here - nighttime on Saturn.
This is a very rare picture, a very rare opportunity where the sun was
behind the planet relative to the spacecraft - as viewed from the
spacecraft. The sun was in a - actually not directly behind the center
of the planet, it was sort of in the 7:00 position, halfway from the
center and you can even see a little piece of the sun getting where the
sunlight is getting bent over the horizon by the atmosphere.

And you can see a little piece of the sun peeping out. It's not - the
sun isn't at that location. It's further towards the center of the
planet but you're looking at the night side of Saturn. And you can see
that it's not pitch black over most of the night side. The only place
that it's pitch black is over the north pole and that's because the
rings are not visible. The rings cannot shine their light on the north
pole or the south pole for that matter because they're over the horizon.

If you just imagine yourself standing right on the north pole, you're
looking straight out to the left or the right in this picture and the
rings - to see the rings you'd have to look down and the horizon's in
the way. So the only place dark enough to detect lightning is in the
north pole and we've looked there and there wasn't any lightning.

The storms that I showed you are all in the southern hemisphere and
they're all at the same latitude, about 35 degrees south latitude. So
it's the ring shine that is confounding our efforts to visually see
lightning. The reason the rings look so different is that you're - this
outer ring is not normally visible. It's only visible in this extreme
geometry where the sun is almost directly behind the Saturn system.

And this outer ring is made of very small particles that scatter light
in a forward direction and the E ring - it's the stuff that's coming
from - it's the result of stuff that's coming off the little moon
Enceladus. And actually Enceladus is in this picture if - at about the
8:00 position on the E ring, there's a little tiny white dot - that's
Enceladus.

All right. So that's the problem is this very bright night side of the
planet. Now, switch gears here - south polar hurricanes. Whether if you
call it a hurricane or not is kind of risky because terrestrial
meteorologists feel they know what a hurricane is and of course they do.
And they sort of bristle at us borrowing their favorite term.

But this thing on the south pole does have an eye and it has a very deep
and very high cloud around the eye. Next slide. There's another one of
these false color images showing cloud height. And the - it has a double
eye actually. The inner eye is sort of oblong. It's not circular and the
outer eye is that circular region. The purple color or violet color
perhaps is deep cloud; the greenish color in this false color image is
high clouds.

And so you can see that there's a sudden transition - there's sort of a
wall of clouds around each of these two eyes. The - let me see - I don't
think this is a movie on your screen. If it is a movie, see if you can
play it. I don't think it is. Let's move on. So this eye and the eye
wall clouds is one feature that makes it like a hurricane. Another
feature that makes it like a hurricane - I'll list the ones that make it
different from a hurricane - that they're sort of obvious.

It's not in the tropics and it's anchored to the poles - that's the most
obvious difference. And there's no ocean to power. But the next slide,
which is labeled temperature and anomaly shows temperature as a function
of latitude in the south pole, in the southern hemisphere. And if you
look at the anomaly - anomaly is just the difference from the mean so
you can see that it's warm.

The red color right over on the right side of this figure within a few
degrees - two degrees of the planet, it's several degrees Celsius or
Kelvin warmer than the further south at the same pressure level; that's
the vertical coordinated pressure - basically altitude. And so you can
see this warm core stretches up from the troposphere where the pressures
are sort of like the atmosphere pressures. A thousand millibars is the
sea level pressure on Earth.

This warm core stretches all the way up into the stratosphere of Saturn
where the pressures are a few millibars. The warm core of a terrestrial
hurricane does not go up that high. It sort of stops at the bottom of
the stratosphere but the value is several degrees warmer, up to five
degrees warmer, are maybe similar to a terrestrial hurricane.

Next slide shows a time sequence over 2.83 hours of watching those two
inner rings. The arrow, the white arrow, is the direction of the
incident sunlight and we're watching this thing over 2.83 hours and the
sun changes its position in the sky. And the time sequence as you can
tell goes down the page and then shifts over to the middle column and
then down the page and then it shifts over to the right column.

And the sun shifts around and the shadows cast by these high wall clouds
also shift around. You can see by the end the shadows are shifted around
in a sort of counterclockwise direction by 90 degrees and they're
basically following the sun. And from the length of the shadows we can
determine how high the - rather crudely, not a precise measurement - but
we can - we take what data we can get and this is the data that you're
looking at - we can determine pretty clearly how high the clouds are and
they're very high.

Next slide - one is labeled inner wall and the other is labeled outer
wall - shows that some of the inner wall especially the eye wall height
does get up to 100 kilometers. Now in Earth, the eye wall of a
terrestrial hurricane gets up to about 15 kilometers so these are indeed
very high clouds on Saturn.

So we're trying to study and actually model using terrestrial -
borrowing models of terrestrial hurricanes and modifying to have no
ocean underneath, trying to understand how you get these wall eyes with
walls when you don't have an ocean underneath. It's a different
mechanism but same physics, different setting but same physics and it's
a puzzle ongoing.

Next, an old friend reappeared from the distant past. The distant past
in this case being Voyager 1981 period, which saw in the northern
hemisphere a hexagon-like cloud circling the pole. And this is a lot
bigger; the eye and the eye walls that I just was talking about in the
southern hemisphere sort of centered on latitude 88 degrees - so they're
two degrees in radius but centered on the pole.

The hexagon, if it were a circle would be at latitude 75 degrees north
so it means a lot bigger structure and the northern hemisphere has been
in darkness for a long time and the spacecraft has not had some good
views of the northern hemisphere. But the first instruments to detect
the hexagon detected it in thermal radiation and of course atmospheres
give off thermal radiation - this is in the infrared, whether it's day
or night.

So putting together images from the thermal radiation revealed the
hexagon. The next slide labeled Saturn north pole, Kevin Baines, Cassini
VIMS instrument, that is a movie and see if you can play it.

Jane Jones: I think on the - the way - the people calling in they needed
to download the movie from the page. Oh. Yeah.

Andy Ingersoll: So if you did, then you'll see it. I'll let you struggle
with it. It's a - I'm going to stop it. The still that starts the movie
is - just shows the hexagon sort of peeking out of the page on the right
and then as the movie plays, it appears that you're seeing motion in the
clouds but what you're actually seeing is the spacecraft flying from
north of the pole down towards the equator and you're just seeing the
motion of the spacecraft.

The next slide, which is a beautiful red with a blue circle, is another
one of these false color images where the red is thermal radiation,
infrared radiation from the clouds and actually, to be more precise,
it's radiation from below the clouds peeping through the holes in the
clouds. So anything that looks red there is - oh, and it's been - let me
see here.

It's - I think it's been reversed so that the - whoa. You'd think I'd do
my own homework. I'm going to figure this out. It is - no it's indeed
what I said. The red is the regions of high infrared emission and the
thicker clouds are blocking the infrared emission from below. You can
see the hexagon there in sort of a black shape and the blue is an aurora
at a totally different wavelength, also infrared but it's sensitive to a
totally different altitude in Saturn's atmosphere, much higher than
these clouds.

And so it's the heat from the aurora that is shown in blue. And the
obvious question is, is there any connection? The aurora is upper
atmosphere, the clouds that are in the troposphere much lower down,
hundreds of kilometers separation in vertical distance. It seems very
unlikely. The aurora is associated with charged particles from outside
the planet following the magnetic field line crashing into the upper
atmosphere.

And why the aurora should have anything to do with the hexagon or maybe
the reverse is true - why the hexagon should have anything to do with
those charged particles is very hard to imagine. I personally don't
think there's any connection except sort of a coincidence here. Why is
there a hexagon if it's not associated with the aurora?

Well, that too is a mystery. Prevailing wisdom is that it's some kind of
a wave in the atmosphere and a wave has to join on to itself if it's a
wave around a latitude circle, it - so it's a wave with a certain
wavelength and it just so happens that six cycles of the wave fit into
that latitude circle. If the wavelengths had been a little longer it
only would have been five so that we could have had a hexagon, a
pentagon, a heptagon - just depending on the wavelengths of that.

Now what excites the waves, keeps it going? We thought that maybe there
was a storm there that was causing the jet streams to deflect around the
storm and that sets off the wave that closes on itself after six
oscillations. That's a theory but no one has successfully modeled it in
a computer simulation. As - next slide - as the northern hemisphere
comes into sunlight, we're beginning to see visible views of the hexagon
and this shows a fairly recent image of the northern hemisphere.

And you can see a corner of the hexagon beginning to peek out of the
darkness and as the sun illuminates more of the northern hemisphere
you'll see more of the hexagon. The equinox, when the sun is just rising
at the pole itself is in August of 2009, which is little more than a
year away. And like the southern hemisphere - next slide - right at the
pole, you can see there's a little hot spot right at the pole.

It's about the same size as the southern hemisphere hot spot. In this
image, a temperature map of Saturn's north pole, hot spot from 89
degrees latitude to the pole, you can see the hexagon sort of
surrounding that little hot spot and it may be that these are very
similar phenomenon. Obviously having a hot spot at the pole is sort of
counterintuitive because, well, Earth's pole is cold because there's
less sunlight there.

And there has to be some fluid dynamical heating going on; it can't be
direct sunlight heating that little hot spot and making it warm because,
after all, the northern hemisphere has not been getting any sunlight for
15 years. So there's some fluid dynamical heating mechanism going on,
which we'd love to understand.

Next, there's something on Earth called the quasi-biennial oscillation.
That means it reappears or it's an oscillation that has a period of
approximately two years. It averages a little longer than that. And it
consists of an oscillation in the wind's speed and direction in over the
equator - not just the equator but the whole tropical region. The winds
blow from the west for a year and then they reverse and blow from the
east for a year and then they reverse again.

And the phasing of the oscillation shifts downward so that the winds
will - the oscillation will start up at high altitudes and then the - so
that the westerly winds, they will start at high altitudes and then half
a year later the winds will be westerly at somewhat lower altitudes and
half a year later than that it'll be westerly at even lower altitudes.

And this is a pattern that rings all around the Earth and there are
accompanying temperature changes; the equator is warmer than the
latitudes on either side for a year and then it's colder than the
latitudes on either side. Well, we can't measure the winds as a function
of altitude or really the stratospheric winds on Saturn at all or only
indirectly because to really do a good job we need little clouds that we
can watch and in the stratosphere we don't have such clouds.

But we do measure the temperatures and the next slide shows that over a
sort of 9-year period, the temperatures have reversed. Obviously this
is - now this is not Cassini data; this is taken from the Earth using
the infrared telescope - and the aspect of Saturn has changed over this
period but look at the line labeled equator and compare it with the line
labeled 13 degrees south latitude.

In 1997 the equator was colder than 13 degrees south latitude and in
2006 the equator was warmer than 13 degrees south latitude. And it
appears that this is a, well - this is spanning a 9-year period so maybe
it's an 18-year oscillation. And Cassini has been participating in this
study looking for reversals in the winds and certainly verifying some of
these temperature changes although they were discovered from Earth
before Cassini.

And it's a very nice example of Earth-based astronomers contributing to
a Cassini mission and Cassini because it's up close and obtaining
detailed observations is helping to further collect data and hopefully
lead to some understanding of this oscillation. Okay. Next slide goes
back to the Earth and shows you this oscillation over a multi-year
period - 25 years. And you can see the red color is a westerly wind -
that means blowing to the east - and then the blue color is the easterly
wind blowing to the east - blowing to the west.

And you can see how the - and you could obtain this pictures at almost
any longitude because it circles the planet and - but you can see how
the winds oscillate and how the patterns start at the high altitudes and
then shift downwards as time goes by. So again we're trying to
understand phenomena that we thought we understood on Earth but in a
much different context.

And you learn stuff - often you learn that your terrestrial
understanding was based on a house of cards but it's sometimes very
humiliating and sometimes very illuminating to study things that you
thought you understood. This just shows the oscillation - now back to
Saturn - how it seems to be oscillating with time.

Okay. I told you about how we don't have a reference frame for Saturn
winds. There's a hope to find one and that is if you get close enough to
the planet, you might detect a very small tilt in the magnetic field; it
has got to be a small tilt because we would have detected anything
larger. But yeah - but a very small tilt is possibly hidden there and as
we're very close to the planet we might be able to detect it.

And so independently the project has been ruminating about how to end
the mission and how to dispose of the spacecraft. You don't want to
contaminate a moon like Enceladus, which has biological potential - you
don't want to contaminate it with a bunch of terrestrial microbes. So
the best place to dispose of the spacecraft is into the planet where
it'll burn up. And that means you've got to spend some time in close to
the planet.

And so we are seriously discussing going - skimming over the atmosphere.
The next slide says end of mission scenario. On the left you can see the
view from above the system and you can see the rings A, B, B, D and then
in between the D ring and the planet there's a white space. That area
seems to be devoid of ring particles and therefore you could send the
spacecraft through there.

Now the right panel shows the kind of orbit a typical high-inclination
orbit, which even at its closest approach does not get in to skimming
the atmosphere; it has to stay outside the rings. But you could take one
of these high-inclination orbits and perturb it with a little thruster
firing and send it just skimming over the atmosphere between the D ring
and the planet.

And this - the next slide shows another spacecraft that's on the books
called Juno, which is slated to orbit Jupiter in a decade or so. And it
has a similar - now Jupiter doesn't have the same enormous ring system
but this is the successive orbits of Jupiter by the Juno spacecraft -
well, if you just imagine this diagram with - make it Saturn and put in
Saturn's rings and say that these trajectories are going between the D
ring and the atmosphere, you'd have our end of mission scenario.

And when you're in that close you can detect the magnetic field, you can
hopefully detect the - well, you can detect any anomalies and any tilt
that exists. You can also measure the gravity field with exquisite
accuracy and the magnetic field and the gravity field tell us about the
interior of the planet; something that's very hard to get at but you've
got to be close.

And really I think I'll stop right there. I'm open to questions.

Jane Jones: Thank you Andy. Does anybody have any questions?

Andy Ingersoll: Is anyone still there?

Jane Jones: Yeah.

(Don O'Coyne): This is (Don) from - (Don O'Coyne) from Bangalore. The
hexagon that we see at the pole, do you believe that it will change when
the tilt changes?

Andy Ingersoll: When the sunlight starts illuminating it.

(Don O'Coyne): Right.

Andy Ingersoll: Well, it was detected by Voyager when it was in sunlight
and so my guess is - and it's lasted for over 20 years. So my guess is
it'll still be there.

(Don O'Coyne): Okay. So it's a permanent fixture. Well, sort of.

Andy Ingersoll: Yeah. Well, nothing - you know, atmospheric features are
not permanent. It's remarkable how long they live on the giant planets
compared with storms on Earth.

(Don O'Coyne): Right.

Andy Ingersoll: The Great Red Spot is 300 years old and is shrinking
right now so it's possible that after 300 years it's lived its life. We
don't know what's going to happen to any of these features.

(Don O'Coyne): Okay. Thank you.

Jane Jones: Okay. Well if we don't have any more questions we'll thank
Andy and then he can get off to his seminar and then we can greet Zibi
to talk about icy moons. And for that everyone will need to go back to
Page 17 of your PowerPoint. That's where the Saturn's icy moon section
picks up. And thank you Andy so much. I think he's already gone. And
Zibi are you there?

Elizabeth Turtle: I'm here.

Jane Jones: Oh great. Okay. Super. So I already introduced you a little
bit earlier from APL. You just recently moved from Lunar and Planetary
Lab - I don't know how recently but\...

Elizabeth Turtle: Yeah, it's been a couple years actually.

Jane Jones: Oh okay.

Elizabeth Turtle: Time flies.

Jane Jones: Time flies when you're having fun. Okay, so take it away.

Elizabeth Turtle: Okay. The 18th slide shows a discovery that was
announced in the last year, which is that the imaging experiment on
Cassini detected the 60th moon identified around Saturn. And you can see
it outlined in that little red box there. And it's not a very big moon.
It's only two kilometers across but it's - 60 is kind of a nice round
number.

There's also a - and the movies aren't in the presentation but there is
a movie that shows the motion of the various satellites here and the
discovery; the motion is what demonstrates that it's a satellite of
Saturn. And if you go to the Cassini Web site you can find that.

Jane Jones: I'll add that movie to the page where the Charm Telecon is
but I'll do it after the fact.

Elizabeth Turtle: Okay. Yeah, the PIA number is 08369 for people who
want to look at it.

Jane Jones: Great. Then I'll add that in the next day or so.

Elizabeth Turtle: Thank you. And there are a couple others that I - a
couple of other slides in here where movies - I've actually sited the
photo journal number at the bottom so people can find them.

Jane Jones: Right. Yeah, we added the Enceladus plume one. So that one's
in there. Okay.

Elizabeth Turtle: Great. So the next slide, Number 19, shows some of the
other small satellites; these are a little larger than the one that was
discovered most recently but these are nonetheless small for satellites.
And they have a fairly unusual shape in that they actually look a lot
like flying saucers.

And there were some papers published this year. The citations are at the
bottom of the slide, describing the shape of these. These satellites are
within the ring system and the shapes of the satellites are consistent
with the satellites consisting of a core. You can kind of see,
especially in the second picture of Atlas there just kind of looking
down on the top you can kind of see a central part of the body that's a
little rougher and then the softer part is actually a little smoother.

And the models indicate that these may be more spherical bodies that
then have kilometers of materials deposited, kind of collected around
the center, around the equators, to form these unique shapes. There
were - going on to the next slide, there were several close encounters
with the various larger icy satellites in the Saturnian system and I'm
going to talk about some of the results from those.

Actually the first set of slides here are images of Dione. We didn't
have a very close encounter with Dione but nonetheless did observe it
throughout the last year. And these observations show the fracture
system on Dione and the craters and we recently released a map of the
surface of Dione that has been observed so far and that's on the 22nd
slide.

You can see the fracture system wrapping around. As Andy mentioned, we
still haven't gotten to the equinox in the northern vernal equinox in
the Saturnian system yet; that will happen in August 2004 - 2009, sorry.
And the - so you'll see in the maps in this presentation that the
northern latitudes are not well imaged yet and that's because they're
not completely illuminated yet.

And as we proceed towards that vernal equinox in another year we'll be
getting more and more coverage of the northern territory. The next slide
has an image of Tethys, of a crater several tens of kilometers in
diameter on the surface of Tethys taken during the close encounter last
summer. And there is another - the slide following that also shows a
fairly dramatic high phase angle view that - there are two of the
crescent of Tethys at - and the one on Slide 24 is a fairly high
resolution and then Slide 25 is pulling back away from Tethys.

The 26th slide shows the big fracture system on Tethys, Ithaca Chasma.
It's quite a dramatic structure. You can actually see on the 27th slide,
which is the full map of Tethys that we released earlier this year, the
extent of this system; it's really quite a huge - it wraps almost half
the way around or almost all the way around the planet and it's quite
deep.

One of the things that has come out of the recent imaging of Tethys is
that a group on the imaging team has counted the number of smaller
craters - you can see that there's a very large crater up, Odysseus, up
in the upper left of the map. And that's actually kind of - the
relationship of where that is on the satellite with respect to where
Ithaca Chasma wraps around the satellite is very intriguing.

But one of the things that you can do is look at the smaller craters and
if you go back to some of the other images you can see that the surface
of Tethys is just covered with craters of different sizes. And you can
look at the number of craters per area on different parts of the
satellite to get a feel for the relative ages because the cratering rate
should be consistent and fairly consistent across the surface of the
body throughout time.

So one of the things that's come out of this study that was published in
the last year was that the cratering - the number of craters per area in
Ithaca Chasma is actually slightly higher than the number of craters per
are in the large crater Odysseus. And it has been hypothesized that the
geometry wasn't a coincidence but this would suggest that it is because
it suggests that the crater is actually younger and that therefore - is
slightly younger and that therefore the two are not related genetically,
which makes the chasma all the more puzzling.

There is also, if you go on to the next slide, Slide twenty - is it 28?

Jane Jones: Twenty-eight.

Elizabeth Turtle: There was a close encounter with Rhea and you can see
on the 29th slide some of the high-resolution images from that
encounter. Especially intriguing on the left-hand side, you can see the
sun and (Ymir), (Ymir) is on the left-hand side, the sun is illuminating
the surface from the left. And you can see at the top that there's a
slope that's exposed and illuminated and that there's actually - it
looks like a tongue of material has flowed down from that.

So this is what looks like a small landslide that's (occurred) on Rhea,
mass wasting being one of the major - one of the primary mechanisms of
erosion. Obviously cratering is clearly happening on the surface as
well. But that slope has clearly been degraded also by some land sliding
down it. The 30th slide shows a stereo view of an impact crater on Rhea
that's on - it's on the leading hemisphere of Rhea.

And if you look, and I should have put in a picture of - a global
picture of Rhea, because there's an impact crater that's actually quite
young that has rays extending out from it. And this is actually that
crater shown close up. Rays are known to form; many satellites have -
and in fact craters on the moon, you can see this as well on our moon -
that the youngest craters have rays and they fade with time.

So this is a - thought to be quite a young crater relatively speaking on
Rhea. And you can see, if you have stereo glasses available, there's
actually a central peak structure and, again, there's been some collapse
downward of material. And there are a number of very small craters
superimposed that may be secondary from the cratering.

There's also a very exciting discovery announced this year that there
may be - the data from the Cassini encounters with Rhea are consistent
with there being a ring of material around Rhea itself. This is
something that's going to be discussed in the next installment of the
fourth anniversary telecon so I just wanted to mention that; it will be
discussed next time.

Jane Jones: Okay.

Elizabeth Turtle: So one of the really exciting encounters of this year
and, of course all of the satellites are exciting in their own right,
but I'm a big fan of Iapetus. And so one of the most exciting encounters
for me was the one last September with Iapetus. It's the only close
encounter with Iapetus in the mission.

It was a very distant one, well a fairly distant one, at the end of
December 2004 and the image on Slide 32 shows what we saw of Iapetus
from that encounter. And that was a really exciting encounter but the
one in last September was much, much closer. So one of the things that's
been known about Iapetus for a long time is that one of the sides of
Iapetus is dark and the other side is quite bright.

And on Slide 32 you see an image of Iapetus from the earlier distant
encounter that Cassini had with Iapetus. And this is an image of the
dark side and this is the image that really - this is the encounter that
really reveals this ridge that runs along the equator of Iapetus. What
we saw in the encounter last September, as shown in Slide 33, is the
other side of Iapetus.

So this is a really good view of the other side. You can see - map out
how the ridge progresses along that side and look at the transition
between the dark and the bright material and get a good look at the
bright side. And some - we got some really spectacular - and not only
scientifically important but also just aesthetically pleasing images of
the surface of Iapetus.

Slide 34 shows a higher resolution view of the bright and dark
transition area that you can see in the global view on Slide 33; this is
just a kind of zooming in. And then 35 shows another higher resolution
image and then 36 has several images of both the bright terrain, which
has some dark materials deposited on it and vice versa and it's really
just a spectacular place.

The 37th slide shows an observation made by CIRS, which is measuring the
temperature, the surface temperature of Iapetus across this transition
region. And this is really important for understanding what is causing
the albedo contrast that we see. And this flyby really provided a lot of
important data to confirm hypotheses about this.

You can see that the dark material is much higher in temperature than
the bright material; the red rectangle shows you where the CIRS data
fall on the visible imaging map. So the dark areas are much warmer
similar - you know, as anything with - that's dark, it will absorb the
heat much more effectively than something that is bright. And this is
part of the key to why Iapetus has this color dichotomy.

The dark areas are actually warm enough that over, you know, a billion
years you can about 20 meters of just water ice, which is primarily what
the surface components of Iapetus - the surface of Iapetus is - 20
meters would evaporate or sublime from the surface at those
temperatures, about 130 Kelvin. That doesn't sound like a lot maybe over
a billion years but it really is.

In the bright areas, there it's much cooler and only about 10
centimeters - so an order of magnitude less ice will actually be able to
sublime from the bright areas because they're cooler. So this supports
the hypothesis that one of the things causing the bright/dark
hemispheres on Iapetus is that the dark material is actually - the
darker areas are warm enough that ice sublimes and then is re-deposited
in the bright regions and that kind of process becomes a self-fulfilling
prophecy that the darker the area gets the less ice there is, the warmer
it can be.

And this is also helped by the fact that Iapetus has a very long
rotation period, I think it's 78 days. So the part of Iapetus that is
illuminated is illuminated and can warm up for a long time. So they also
got temperature maps, I don't have them here but they also did map the
night side - CIRS mapped the temperatures of the night side as well and
those are consistent with the very (plucky) material that cools off
quite quickly.

So the next slide shows observations of Iapetus that were made by UVIS
in the - this is an Ultraviolet Imaging Spectrometer and these are a
couple of different maps showing what UVIS saw. UVIS is looking at the
composition of the materials on Iapetus and those maps show differences
in the materials.

And the UVIS observations are also consistent with the hypothesis that
the volatiles are being lost at low latitudes and transported to the
colder high latitudes. They're also able to look at differences in the
composition within the dark and bright areas to try to see how much it
varies across that. The 39th slide has a similar observation made by the
Visual Imaging Mapping Spectrometer - Visible and Infrared Mapping
Spectrometer, sorry.

They too are looking at the composition of Iapetus but in the infrared
part of the spectrum. And these - their observations show that - so
again, that most of Iapetus is composed of water ice but there's a
stronger signature of carbon dioxide in the dark terrain. And there are
also some trace amounts of other organic materials and possibly ammonia,
although there's still, I believe they're still trying to sort out the
calibrations to confirm that.

There are also some spectral features that actually don't match any of
the compounds that are known or in the databases to which they're
comparing the observations and that's pretty intriguing, especially
because a lot of those features are also observed in the dark material
on some of the other satellites, especially the outer satellites -
Phoebe, Dione and in the rings.

So it suggests that a lot of the - that the origin of some of this
material is the same for various parts of the Saturnian system. So
that's - it's interesting that those are consistent. One of the big
questions is what the origin of the dark material is. I mentioned that
it becomes kind of this run away process; you get a dark area and that
it becomes warmer and then it becomes harder for ice to persist in that
area and it - you get this run away process where the ice is transported
from the dark areas to the bright areas.

But that needs an initial deposition of dark material to get it started
so one of the things that's interesting - you'll see in some of the
upcoming slides, which are also images of Iapetus up close starting with
Slide 40 - this is an image of the ring - the ridge that runs around the
equator or most of the equator of Iapetus.

But in the center top, you'll see that there's a small, bright impact
crater. And we can use the impact craters to assess the thickness of the
dark material on the surface of Iapetus. Most of these craters actually
don't have a strong albedo difference but - and there's that one and
there really are only a handful of these really bright craters that are
punching through.

The fact that they're small indicates that the layer isn't that thick,
that they can punch through it - that even the smaller craters can punch
through it. And now that we have these really high resolution images of
Iapetus, we can see that even craters on the scale of several tens of
meters are punching through, which suggests that this material is only
maybe several meters deep before you get down to the brighter ice
underneath it.

And that of course begs the question of why the larger craters are still
dark, which suggests that not only did - was there some - has material
been in place on Iapetus to start this process of transport of the ice
away from the dark regions but it must continually be being in place
such that it's coating the larger craters again.

And this is consistent with some of the other instruments' observations
like UVIS and CIRS as well. So the 41st slide also shows a nice high
resolution view of Iapetus and the 42nd slide shows the map that we can
now put together because we've seen both hemispheres fairly well. The
ridge runs most of the way around but it is incomplete; in some areas
it's interrupted.

At about 30 degrees west longitude you can see that the ridge is
interrupted by a huge impact basin. In other areas it may not - if it
doesn't exist or we don't see the ridge but there isn't necessarily an
impact crater there to obscure it - it's not clear what the origin of
this ridge is; it's really - it's surprisingly difficult to explain how
a feature like this, which is clearly a fundamental feature to Iapetus,
how it formed and that's something that's still being researched.

One of the other things I should mention about Iapetus is that we
actually approached - Cassini approached Iapetus during the flyby from
the un-illuminated side but the radar instrument was actually mapping
Iapetus at that time and so we have a radar map of Iapetus.

And we have radar observations of the surface because they can probe
into the sub-surface of Iapetus to some extent, also give us information
about the mixing - the characteristics of the dark and bright materials
on the surface of Iapetus and the mixing and so that's going to be very
interesting as well.

The 43rd slide shows one of our best images of Epimetheus, which is a
small satellite. It's about 100 kilometers - I'm sorry, yeah, its about
100 kilometers in diameter and it's - this is - it's clearly a cratered
body but it's not completely covered in craters. In fact, it has a lot
of areas that aren't cratered, which is interesting. You can also see
that there are a couple of different units of material.

There seems to be this kind of gray materials that's collecting down in
the bottoms of craters by mass wasting and maybe in other low areas on
the surface. And last but certainly not least, there was a very close
encounter just this past March with Enceladus.

The image on Slide 44 is actually an older image, one of our kind of
best global views of Enceladus demonstrating the incredible diversity of
the land forms on its surface, including the - this is a very false
color, very enhanced color view - but including the tiger stripes down
at the south pole. And the 45th slide, again, is an image from one of
those earlier encounters that shows the tiger stripes from a little
closer.

Later, just a few months after that image was taken, this movie was put
together of the plumes on Enceladus and by looking at how the - if you
download that movie from the Web site, you can see that the plumes move.
And you can use that parallaxes caused by the motion of the spacecraft
to trace - you can trace back to where the sources of those plumes must
be on the surface.

And the Slide 47, the image on that slide shows the results of analysis
done by (Jeff Talling) and Carolyn Porco that was published last year.
The - it's a very busy graphic but the yellow roman numerals show the
places where the sources of those plumes must be to be consistent with
the parallaxes observed as you - in that movie. The red diamonds or some
of the - I'm sorry, the smaller diamonds actually show some of the -
where the CIRS instrument has seen hot spots as well.

You can see that the - a good correlation there. And CIRS got more data,
this is from the earlier encounter; CIRS got more data in the more
recent encounter and I'll be getting to that. You can see that those -
that the plume sources are correlated with the location for the most
part of the tiger stripes. Just last fall, you can see on Slide 48, a -
on the left an image of Enceladus that was taken.

And on the right, a graphic illustrating the path of a star that UVIS
watched as it traversed behind the plume. And this is a really important
observation; the 49th slide shows where this - shows the tracks of the
star, as kind of shown above the surface of Enceladus and again those
same plume sources are listed.

So one of the really important things that came out of this observation
made by the UVIS instrument had to do with the size of the particles at
this altitude above the surface of Enceladus because the Cassini
spacecraft flew quite close to Enceladus in the encounter in March and
of course we want to make sure that it's safe to get that close to that
source of the plumes, the encounter in March, the closest approach is
only 50 kilometers but that wasn't over the plumes. Cassini was higher
than that over the plumes - I think about 250 kilometers.

Nonetheless, that's close and we want to make sure it's safe so that was
one of the really important results to come out of that observation. The
next slide actually shows those encounters. On the left is a graphic of
the 2005 Enceladus plume observations and on the right is a graphic
showing Enceladus and the plumes and the path of Cassini's various
encounters. So we've actually only had three of these encounters so far;
the one in kind of teal, that's labeled E-3 is the one from this past
March.

And there are several more encounters with Enceladus planned for
Cassini's extended mission for the next couple of years, some of which
will get closer in within the plumes. From the March flyby, the slide on
Page 51 shows the results from the Ion and Neutral Mass Spectrometer,
which actually measures the composition of material as it passes through
it. This instrument is also very important for understanding Titan's
upper atmosphere and the composition of that.

But it's wonderful for flying through Enceladus' plumes and
understanding what the materials within that are. And of course there's
a lot of water vapor - that's what seems to be driving the plumes,
although the actual mechanism for that is still being debated.

There's primarily water vapor but there are also a fair amount of
organics and intriguingly the organic composition is actually closest to
that of comets, which would not have been expected for, first of all, a
satellite in the Saturnian system, which is likely to have gone through
the formation of the Saturnian system and therefore would not be
expected to be as primitive as a comet. And also a satellite that is
clearly active and therefore has gone through a fair amount of thermal
processing as well.

So it has a fairly primitive composition of materials being (expelled)
from within and is a puzzle. One of the other observations from the
encounter last March is higher resolution views of the surface
temperatures. CIRS saw that in the very first Enceladus encounters - saw
that the south pole was much warmer than one would expect for a small
(icy) body sitting at that distance from the sun.

And on Side 53 you can see one of their higher resolution observations
from this most recent encounter. The asterisks again indicate the
locations of the triangulated plume sources and you can see that those
correlate with these warm regions along - that run for the most part
along the tiger stripes, right along those fractures. And the
temperatures on the surface there are about 180 Kelvin. The peak
temperature is about 180 Kelvin, which is surprisingly high for such a
small satellite.

The equilibrium temperature at this distance from the sun is 72 Kelvin
so it's clearly very, very warm compared to what you would expect for
the surface of Enceladus. The last slide I have actually in the
discussion of the satellites is actually Enceladus' northern territory
and, as I said and Andy said, we're only just at the northern most
portions of Saturn in the satellites are only just becoming illuminated
as we get towards northern spring.

The northern part of Enceladus is very, very different from the southern
part. It's quite cold and it has a lot of impact craters if you compare
that to some of the images of the south pole. The south polar terrain of
Enceladus basically has no impact craters at the resolutions we've
observed it at. And if you look at the north pole, it has a lot of
impact craters; more over those impact craters are deformed in a way
consistent with relaxation.

This is something that can happen if the ice is warm enough to be mobile
over geologic time and clearly for Enceladus that's the case. And that
also provides really important information as to the geologic history of
Enceladus and its interior conditions. So we'll be really looking
forward to viewing the northern hemisphere of Enceladus as it comes out
of the winter darkness and mapping and completing the map of Enceladus.

There isn't - the next Enceladus encounter is, I believe, August 11, so
that's coming up quite soon and should be very exciting. So I'll leave
that there and take any questions.

Parker Moreland: Hello?

Jane Jones: Yes. Go ahead.

Parker Moreland: Parker Moreland, McCarthy Observatory. A couple of
simple questions. One, are all of the icy satellites that you have been
going through, Libby (sic), phase locked with Saturn?

Elizabeth Turtle: Yes. They are all - all the ones I've been speaking
about are. It turns out Titan may not be and that's something that I'll
talk about in next month's...

Parker Moreland: Okay. But certainly Enceladus and Iapetus are phase
locked and actually have a leading side.

Elizabeth Turtle: Yep. They do.

Parker Moreland: Now, I have a question that's been bothering me since
it came out and that's Slide 61. It was actually earlier but I hesitated
to delay our speaker then. The eclipse slide. I cannot understand\...

Jane Jones: This is the nighttime on Saturn slide. Yeah. Number 61 in
Andy's presentation.

Parker Moreland: Nighttime on Saturn, 61 on the PDF...

((Crosstalk))

Jane Jones: Number 61 in Andy\'s presentation.

Parker Moreland: Right.

Elizabeth Turtle: It's the solar eclipse from Cassini.

Jane Jones: Right.

Parker Moreland: Right. I've been looking at that for years and I cannot
understand why I can see rings in front of Saturn in the dark. They're
offset from the rings that are coming around but I still see rings here
on the dark side. Is that some kind of reflection phenomenon of the
light bouncing off of these near side rings back on to Saturn and making
it appear that I'm seeing rings in front of Saturn even though, you
know, I can't be. It's dark here, I guess.

Elizabeth Turtle: The image in that slide, that one is very stretched to
bring out the\...

((Crosstalk))

Parker Moreland: ...or something?

Elizabeth Turtle: But that doesn't mean those are artifacts. It's just
that you're seeing, you know, you're seeing very faint features. But
there is a reflection from the rings of light back onto Saturn and there
is also scattering from dust that's illuminating part of that.

So I think the source of illumination there is reflection onto the night
side of Saturn and maybe reflect...

((Crosstalk))

Parker Moreland: The same problem that he was worried about. He can't
get a nice dark thing for his lightning strikes.

Elizabeth Turtle: Right.

Parker Moreland: But the alignment is such that it almost looks like you
have continuous rings into a shadow area and so it can be a little
disconcerting (at first). Okay. I think we just\...

Elizabeth Turtle: Yeah. And the rings look very different in different
lighting conditions. So\...

Parker Moreland: Right.

Trina Ray: So just to clarify that a little bit, we did a Charm Telecon
with (Matt Headman) and I'm just bringing it up right now, where he
talked for about 20 minutes about this image alone. And he drew like 20
different slides where he drew every line of sight from the sun hitting
the rings, hitting the planet, going through the rings and being - and
getting to your eye; it was fantastic.

And I'm just looking to see when this was - it's been recent. Oh Jane,
help me.

Jane Jones: Okay. Let me get there.

Trina Ray: Saturn's Rings Large and Small. Was that it?

Jane Jones: Let me see.

Trina Ray: Probing (Mysterious) Iapetus - no, no, no. We had so many
great Charm Telecons. It was in October I thought. No, it can't be
October. Well, you know what, of course, here I've interrupted the whole
talk and\...

((Crosstalk))

Elizabeth Turtle: ...yeah.

Trina Ray: But if you just go back, there is a terrific Charm Telecon
and I'm almost certain that it's Saturn's Rings Large and Small on July
31, 2007 where (Matt) talks about that.

Jane Jones: I'm pulling it up just to see if that's what it is.

Trina Ray: And it's just - this image can fascinate you for hours. But
that's exactly what's happening is the sunlight is coming in, it's
hitting the rings, it's bouncing off the rings and hitting the planet
and making the southern hemisphere of the planet a little bit brighter
and bouncing off the planet and heading back towards your eyes.

But of course the rings are still in the way so there you see the shadow
of the rings. So the rings are actually blocking your view of the
southern hemisphere on that band where they look dark right in the
middle of the image. And this - it's completely real. This image is
completely real. The only parts of this image that are image artifacts
are the very weird streaks that are outside of the planet itself.

Parker Moreland: Right. Yep. The propellers.

(Curt): Trina, this is (Curt). That Charm was on 11-28-2006.

Jane Jones: Yeah.

Trina Ray: 11-28-2006. Thank you so much.

Jane Jones: Yeah, I was just digging that up.

Trina Ray: A New Perspective of Saturn's Rings, yeah. So if you go to
where you downloaded the presentation and take a look at (Matt)'s
presentation from November 28, 2006, he literally has 14 pages where he
lays out this image.

Parker Moreland: Okay.

Trina Ray: And it is well worth the time to take a look at it.

Parker Moreland: Will do it. Thank you so much. I'm glad I asked the
question.

Matthew Ota: Question and comment.

Jane Jones: Go ahead, please.

Matthew Ota: Okay. This is Matthew again with the Saturn Observation
Campaign. On Slide Number 48 (unintelligible) about Enceladus' plumes,
the graphic representation on the right shows the location of the plumes
in relation to the entire satellite in the south polar regions.

My assumption is there's no other plumes that have been detected on any
other areas of that moon, which begs the question of does that
particular plume have any effect on Enceladus' orbit because I believe
you're showing the velocity vector with that arrow - the orbital
velocity vector?

Elizabeth Turtle: The arrow is actually showing the star. That's just
showing the path the star took behind the plumes.

Matthew Ota: Oh. Okay.

Jane Jones: Yeah, that's just the occultation.

Elizabeth Turtle: Yeah.

Matthew Ota: Okay. I was thinking of comets and how they have jets, you
know? And the jets on comets actually change their trajectories and
whatnot. Is there enough mass in these plumes to appreciably alter
Enceladus' orbit?

Elizabeth Turtle: Well, I'm not an expert in that. It probably depends
on your definition of appreciable. It's - I don't think it's affecting
the dynamics dramatically. I don't know if there's detectable - I mean I
don't think we'd be able to detect it on the timescale that we're
observing Enceladus.

Matthew Ota: Okay.

Elizabeth Turtle: Over the longer timescale, it might be something that
would be detectable - I mean over a very long timescale, probably not
one we would be able to do. But I'm not a dynamicist I'm afraid.

Matthew Ota: Okay.

Elizabeth Turtle: The - it is unique to the south pole. There have not
been plumes observed anywhere else on Enceladus. That's the part of
Enceladus that is warm and CIRS has observed other parts of Enceladus
and they are not warm. The north pole for example because it hasn't been
illuminated at all is sitting down at something like 30, 40 Kelvin; it's
really quite cold.

So this is completely anomalous. It may not be a coincidence that it's
at the south pole in that if there is a difference in the (shape) or the
mass distribution in Enceladus because of this activity, it might - it's
possible that the poles would rotate such that it - or that that region
would rotate such that it were at one of the poles just from the
dynamics.

So it may not be a coincidence that it's at the pole. That may have
happened because of the internal structure beneath this region. But it
is the only area that's active now. There are some other areas on -
there's one or two other places on Enceladus that have similar looking
tectonic features; the geology looks similar.

And so it's been suggested that those might be areas that used to
exhibit this kind of activity and that are no longer and now this area
that's currently at the south pole is active. So it's possible that this
has happened other places at other times but the full geologic history
of Enceladus is still being studied.

Matthew Ota: Okay. And then the comment is for Slide Number 46,
Enceladus' plume. I did go to the Web page for the movie and I just want
to comment that to download the animated GIF file, you have to right
click over the image and do a Save As - Save Image As operation because
the other options are TIF and JPEG format, which of course are not
animated.

Jane Jones: There\'s several places to get that movie in addition to the
photo journal. That's one place and then there's also in the Cassini
movies - it's also there, too, in four different formats of movies.

Matthew Ota: Okay. Okay. Thank you. Thank you.

Parker Moreland: (Libby) (sic)?

Elizabeth Turtle: Uh-huh.

Parker Moreland: Parker Moreland again. It seems to me that we have to
come up with a heat source for both Enceladus and Iapetus. What's the
best thinking? The only thing I can think of is radioactivity but what
is everybody out there thinking about as a heat source to cause all this
stuff?

Elizabeth Turtle: Well, it's harder for Enceladus than Iapetus.

Parker Moreland: Yes it is.

Elizabeth Turtle: Iapetus - well, and it's not to say that Iapetus is
simple because the ridge on Iapetus and the shape of Iapetus actually
really complicate that as well. It's something I didn't talk about today
but from the December 2004 encounter with Iapetus, you can see that the
shape of Iapetus is actually much more oblique than you would expect
given the fact that it's got a 78-day rotation period, which suggests
that the early - it's got I think the - if I remember correctly, the
shape of Iapetus is consistent with a hydrostatic - (unintelligible)
hydrostatic equilibrium rotating at 17 hours.

So that implies that it's frozen in to Iapetus - the Iapetus shape froze
in and has persisted in that state despite the fact that Iapetus is now
(default) entirely locked for its system orbit. So Iapetus has to have
been warm enough to deform to that shape - for the faster rotation rate
and probably have to, you know, if the ridges - if the tectonic
features - then that also has to be explained somewhere in there early
on.

And yet it has to have cooled fast enough that that locked in and has
been able to stay stable over 4 billion years of history. So the timing
on Iapetus is actually quite tricky. To model that all using the short
and long-lived radioactive thesis and get it to be warm at the right
times and cold enough quickly enough that it froze in and has persisted
is actually non-trivial.

Parker Moreland: So we don't think it was at one time close to Saturn
and it got tidal heat like Io and then somehow it got knocked out to
where it is now? That does not\...?

Elizabeth Turtle: No.

Parker Moreland: Okay.

Elizabeth Turtle: No it's - for Iapetus it looks like it's - I believe
the history is such that it does not have to have moved significantly
within the system.

Parker Moreland: Thank you.

Elizabeth Turtle: Enceladus is also hard to explain. And it depends; you
can look at it, you know, one way or the other. Either Enceladus or
Mimas is hard to explain because Mimas is actually slightly closer to
Saturn and yet it has no activity at all. It's got one oldest surfaces
in the system.

And so somehow these two satellites that are about the same and in about
the same part of the Saturnian system, have had hugely different
histories. Again, for Enceladus, unless you appeal to deus ex machina
explanations for the plumes, and that's not out of the realm of
possibility of course, but we like to not have to rely on that as an
explanation.

The radioactivity and the tidal heating are sufficient to keep Enceladus
warm if it never cooled off. So if this region on Enceladus that has
persisted as warm throughout its history - you can, I believe the most
recent studies that I have heard the results of, you can keep it warm.
There's enough tidal heating to maintain that heat through the history
of Enceladus.

But if it ever cooled off there's not enough tidal heating through the
evolution of its orbit and the orbits of the other satellites; there's
not enough to heat it back up again without some external event. So
you're right, it too is difficult to explain but it's possible that the
radioactivity early on and given the radioactivity early on and the
resonances, the tidal activity, there's enough of that to keep it warm
if it never cooled off.

Parker Moreland: Thanks much.

Jane Jones: Okay. If nobody has any other (questions), let's thank Zibi
for her really great talk. I loved having all the comparisons from all
the other instruments besides the ISS on that. It was a really, really
nice presentation. Our next Charm will be July 29 where we'll cover the
other three of the five Cassini science objectives.

Today we've covered Saturn and the icy satellites and on July 29 we'll
cover maps, the magnetospheric and plasma science results for the fourth
year and rings, Titan and Trina will wrap it all up with some cool,
gee-whiz facts. Anybody have any other questions or comments?

Parker Moreland: Same time?

Jane Jones: It's always the same time. Are you a - which group are you
with?

Parker Moreland: McCarthy Observatory.

Jane Jones: I mean which - how did you get your invitation?

Parker Moreland: Oh, museum.

Jane Jones: Museum Alliance. Okay. Great. Yes, the announcement that
comes out every month says at the bottom that these are always at the
same day; it's always the last Tuesday of the month, always 11:00 to
1:00 pm. And then the topics change every month. But you'll be getting
another invitation from the Museum Alliance with all that information in
a couple weeks. Thank you everybody.

Trina Ray: Thank you.

Jane Jones: Okay bye-bye.

Trina Ray: They finally started going after the little toys in the
(unintelligible).

Jane Jones: Hey Trina.

Trina Ray: Oh hey Jane. I was just calling in to get the numbers. I just
pressed star, 0 and so I'm waiting to be connected with the operator I
hope. (Put) that in an email to (Amanda)? Thirty-two people is how many
we had online today. Can you drop that in an email to (Amanda)?

Jane Jones: Oh yeah - oh you already got that. Thank you.

Trina Ray: You're welcome.

Jane Jones: I was just waiting to do that myself. Yeah, that was an
awesome, awesome presentation. Yeah.

Trina Ray: Presentation. Yeah.

Jane Jones: Although I found two boo-boos and I corrected them but they
didn't make it in. So\...

Trina Ray: Oh well. We'll catch them next time.

Jane Jones: No, no, no - they'll get corrected.

Trina Ray: Yeah.

Jane Jones: But one of them, the cover slide said Cassini's third
anniversary.

Trina Ray: Ouch.

Jane Jones: And then the moon page said we had 47 moons.

Trina Ray: Oh yeah. We didn't catch that once.

Jane Jones: Yeah, I caught it but didn't get it - but anyway, (Curt)'s
making those changes.

Trina Ray: Okay. Okay well thanks so much for hosting today because I'm
still home sick.

Jane Jones: Okay. Oh you're welcome. Yeah.

Trina Ray: And so I'll be in tomorrow though.

Jane Jones: Okay I'll talk to you then.

Trina Ray: Okay. Bye Jane.

Jane Jones: Bye-bye.

END