**NASA**

**Museum Alliance**

**June 1, 2004**

**2:30 p.m. CDT**

**Overview**

**Amanda Hendrix of the Cassini Science Planning Team discusses plans
for investigating Saturn's eight medium-sized icy moons.**

Coordinator At this time, I'd like to inform all participants that
today's conference is being recorded. If you have any objections, you
may disconnect at this time. Thank you. You may begin.

Jane Since we're just starting to record, I'm going to introduce Amanda
again, so that it gets caught on the transcript. Our speaker today is
Amanda Hendrix from the Cassini Project. Amanda grew up in Pasadena, did
her undergraduate work at \[California Polytechnic University\] San
Louis Obispo, her graduate and post doc at the University of Colorado in
Boulder in the Aerospace Engineering Sciences Department, specializing
in ultraviolet reflectance from planetary surfaces.

She's been at JPL for 3.5 years now, and she works in the Cassini
Science Planning Team, focusing on planning for icy satellite flybys.
She's also on the Cassini UVIS team, and that's the Ultraviolet Imagine
Spectrograph instrument. She will be analyzing UV data of the icy
satellites, including CB. Now, without any further delay, here's Amanda.

Amanda Thanks, Jane. I understand that not everybody has the handout, so
hopefully, it will be clear what I'm talking about; but if not or even
if you do have the handout, please feel free to interrupt me with
questions as we go along. As Jane said, I'll be talking about the icy
satellites of Saturn and the observations that we're planning on doing
with the Cassini spacecraft.

On page two, I'll just kind of talk generally about the satellites.
Saturn currently has 31 moons that we know about, but certainly, we
expect that the Cassini spacecraft will discover more moons. Back when
Cassini was launched in 1997, there were only 18 known moons of Saturn.
So since then many have been discovered, and we expect that at least
several more will be discovered while we are orbiting Saturn during the
four-year tour.

The Cassini Satellite Orbiter Science Team, also known as CSOST, is the
group that plans the science observations that will occur during the
flybys of the eight major icy satellites. So the CSOST group is not
concerned with Titan, and it's not concerned with the other small
satellites, which are also known as rock. The satellites that we work
with are Iapetus, Rhea, Dione, Tethys, Mimas, Enceladus, Hyperion, and
Phoebe. These satellites were all discovered between about -- early on,
Cassini discovered Iapetus and Rhea in 1671 and 1672, Dione and Tethys
in 1684. Herschel discovered Mimas and Enceladus in 1789. Hyperion was
discovered by Bond and Lassell in 1848, and Phoebe was discovered,
finally, in 1898 by Pickering. These are all sort of considered medium
sized satellites. They're not as major as Titan, and they're not as big
as the Galilean satellites of Jupiter, for instance, but they are bigger
than the smaller moons of Saturn, which are more like big rocks.

Mainly the icy satellites are made up of ice, water/ice, and some sort
of contaminant because we can tell that they're not pure ice, but
water/ice has been detected on all of these moons, at least in some
quantities. But we also expect, due to their position in the solar
system, that ammonia and methane may be present. They haven't been
detected yet, but we expect that some of the instruments onboard Cassini
may be able to detect those species.

Now all of these moons, except for Phoebe and Hyperion, are tightly
locked, which means they orbit Saturn synchronously, keeping the same
face towards Saturn all the time, just like our moon.

If anybody has any questions about this slide, please feel free.
Otherwise, I'm going to move on to the next one.

On page three, I include here pictures from Voyager of all eight of the
satellites that we're talking about, and from left to right, top to
bottom, they go in order of their distance from Saturn. Mimas is the
closest of the medium sized satellites at about three R~S~ \[Saturn
radii\]. It's also pretty small. It's only about 200 kilometers in
radius. Next out is Enceladus. Back to Mimas. Mimas is unique because
it's dominated by this huge crater, which you can see in the image here.
It's a crater called Herschel, and it makes Mimas look a lot like the
Death Star in *Star Wars*, so Mimas is also sometimes known as the Death
Star.

Jane There's a copy of a slide very much like this on the Cassini images
Web site on our Web site under multimedia images and then, you go to the
large moon section, and there's slides that show the relative sizes of
all of the icy satellites. This looks very much like Amanda's slide.
\[http://saturn/multimedia/images/large-moons/index.cfm\]

Amanda Although here I should stress, that I put the radius of each of
the satellites on because I have the scaled images to scale.

Jane Yes. That's much better.

Amanda It's approximately right, but not even close to being correct,
but I just wanted to make them all big enough, so you can---

Enceladus, the second moon out at about 4 R~S~, or Saturn radii, is a
little bigger than Mimas at 260 kilometers in radius, and Enceladus is
unique because basically it's the brightest body in the solar system. It
has an albedo or reflectance of one, or maybe even higher than one,
which is about has high as you can get. You can see in the image here in
the handout that some regions are very smooth. There are other regions
on Enceladus that are more cratered, so it isn't completely a billiard
ball, but there are some regions that are quite smooth.

This leads people to think that there's been some recent resurfacing,
some geologic activity, such as perhaps ice volcanism that could have
led to these smooth areas. The fact that it's very bright means that
there are very few contaminants, which means that, perhaps, the surface
hasn't had time to be contaminated with outside material.

Tethys is the satellite that's next out at almost 5 R~S~. This is a
bigger one. It's 530 kilometers in radius, and it's characterized by its
very heavily cratered surface. It also has a very big crater on it,
which isn't shown in this image here. It's called Odysseus. It's on the
other side, but interestingly there is a big, huge groove that covers
about 270-degrees of the satellite, and that is shown in this image
here, kind of running across the middle of the moon there. It's possible
that when the impact that formed Odysseus happened, it also created a
big crack in the surface that's opposite the Odysseus crater. This is
called Ithaca Chasm.

Next out is Dione. It's a little bigger than Tethys, and it orbits
Saturn at about 6.3 R~S~. Dione is characterized by these kinds of light
colored wispy streaks that are particularly apparent on the trailing
hemisphere, so I said that they are tightly locked, and the trailing
hemisphere is opposite the hemisphere that leads the direction that is
in the direction of motion, so the Saturnian hemisphere faces Saturn.
The leading hemisphere is facing the direction of motion. The trailing
hemisphere is opposite that, and Dione's wispy streaks are primarily on
the trailing hemisphere. The source of these wispy streaks is unknown.
It's not clear whether they come from an exogenic source or whether they
are endogenically derived.

Rhea, the next satellite out, has similar wispy streaks. They're not
quite as apparent as Dione's, and these appear on a slightly different
part of Rhea than Dione. It's more sort of on the anti-Saturnian
hemisphere of Rhea, but it's really interesting that both of these
satellites have these wispy streaks. Rhea is the biggest of the icy
satellites at 765 kilometers in radius and it orbits about 8.75 R~S~.

Now we have kind of a gap in the medium-sized satellites because this is
where Titan orbits, but then Hyperion is the next of the icy satellites
out, and that's about 25 R~S~. It's small. It's only got a radius of
about 140 kilometers, and this is the mean radius because Hyperion is
unique in that it is irregular. It's not a sphere, and it's the largest
body actually in the solar system that is not a sphere because generally
at about 100 kilometers, things start to converge into a spherical
shape. And so Hyperion is unique in that it is non-spherical, and it's
extremely battered in appearance. You can also see that it's a slightly
different color. It's dark, and it's kind of reddish in appearance as
well.

Iapetus is the second biggest of these icy satellites at about 730
kilometers radius orbiting at 58 Saturn radii. Iapetus is unique because
it has a very distinct and mysterious albedo dichotomy. The leading
hemisphere, which is in this picture in my handout on kind of the left
side, the leading hemisphere is very dark. It's one of the darkest
surfaces in the solar system, and visible wavelengths, it only reflects
about 4% of the light that hits it. It's very, very dark, whereas the
trailing hemisphere is relatively bright. It's not as bright as some of
the other surfaces, but it's about 60% albedo. There's a fairly distinct
boundary between the dark areas and the bright areas.

The source of the dark material or the reason that the leading
hemisphere is dark is unknown. It's possible that dark material was
emplaced from an outside source, and it covers only the leading
hemisphere because Iapetus is traveling into, perhaps, a stream of dust
coming from some other source. It's also possible that it's
endogenically emplaced. Meaning that Iapetus has dark material
underneath the surface that has been exposed, due to perhaps meteoritic
bombardment, which is eroding away the icy, thin surface on the leading
hemisphere. Those are just two of the options for where the dark
material might be coming from and why it's only on the leading
hemisphere of Iapetus.

Now it's possible that Phoebe, and I'll talk a little bit more about
this later, but it's possible that Phoebe, the next satellite out, which
is dark, Phoebe material or Phoebe dust is the source of the dark
material that is exogenically emplaced on Iapetus' leading hemisphere,
if it is exogenic.

On to Phoebe, the smallest of these sort of medium sized icy satellites
at about 110 kilometers in radius, and it orbits way out at 215 R~S~.
Phoebe is on all of our minds these days because we're all very excited
because the Cassini spacecraft is about to fly by Phoebe. We'll have the
Phoebe flyby on June 11^th^, which is next Friday, and we'll get data
down on June 12^th^, and so we're all really excited to have this first
big event in the Saturn tour happening so soon. It's actually not next
Friday, but the Friday after next week.

Any questions in general about the icy satellites here?

M I did have a silly question. I notice on Mimas, Tethys, and Iapetus,
the crater features on the handout, some craters are quite similar in
appearance with the center projections in the center of the crater. Any
ideas or thoughts? I'm an amateur, so I'm not sure what would cause
that. It seems to be fairly unique.

Amanda A central peak is a common feature in craters, and you'll see
them on Earth's moon as well, but as the craters get older and older,
that central peak will go away. It'll degrade away, so if you see a
central peak, it's a sign that that not a whole lot of degrading has
gone on since that---

M It's a younger crater by comparison.

Amanda It's a relatively young crater. Now, the differences between
Earth's moon and these satellites is, of course, that these are made of
ice, and so what happens when you make a crater is different, and so the
ice is more fluid than the materials that make up the moon, and so a
central peak may be more easy to make, basically, and maybe longer
lived.

M Thank you.

Amanda I want you to keep in mind that the resolutions on these images
are all different, so even though Tethys is highly cratered, but it also
looks like in this image because this is a higher resolution image than,
say, the Dione image. Dione has got plenty of craters as well, but it
just isn't clear from this image here, for instance.

Another thing that I wanted to tell you about is about Enceladus. You
know I was mentioning how potentially there's ice volcanism or some sort
of geologic activity that makes these smooth plain areas. Another idea
that people have is that the e-ring, which is the outermost ring of
Saturn, and it's also very extended. It's tenuous, but very broad,
relative to the other rings, but it's possible that Enceladus is
actually the source of the material in the E -ring. Enceladus, Mimas,
and Tethys all orbit within the E-ring, and so they sort of bathe in
this E -ring material as they orbit Saturn; but it's possible that
material from Enceladus either geologically derived or sputtered away by
charged particles is creating this E -ring material.

Jane, maybe on the Web site there's an image of the E-ring or a drawing.

Jane Yes. Again, from our home page, go to the multimedia section, and
then under there is images. Go to rings instead of satellites of icy
satellites, and you'll find a really nice -- there's a Saturn systems
roadmap that shows. \[http://saturn/multimedia/images/rings/index.cfm\]

Amanda Yes, but the one that I really like is Saturn satellites and
rings in the third row down, the fourth one over.

Jane Yes. That one is really nice.

Amanda Actually, it's a little different than I thought it was going to
be. There's another one.

Jane There's two versions of this slide.

Amanda Yes.

Jane They're both made by the same person who works on our Cassini team,
but he's got two different versions.

Amanda But what you could tell from this Saturn systems roadmap or the
other one is that the E-ring is very broad and tenuous, and it's
basically centered on Enceladus, but actually the E-ring material
extends into Mimas and out to Tethys. It isn't super clear from this one
image, but in another one of ... drawings, it is more clear. We'll learn
more about that. That's one of the really exciting things that we'll
learn about with Cassini is whether Enceladus is geologically active or
not, and whether it is in fact the source of the E-ring, and what
process goes on to cause the E-ring to be formed.

Jane We'll send these two slides out to people if you want them, or
where the URL is for these two images for those people who might not be
at their computers.

Amanda I wanted to make sure. I said that water/ice is the primary
constituent of all of these moons, which the exception of Phoebe. Phoebe
is very dark, and does contain water/ice on the surface. It's only
recently been discovered that the water/ice bands in the IR \[infrared\]
have been detected from Earth, but it does seem to be the water/ice may
be in distinct areas on the surface. It's possible, so in the Phoebe
flyby in the next couple of weeks, we'll be looking, analyzing the data,
looking for water/ice and other species and seeing how they're
distributed on the surface, we'll tell you a little bit more about that.

On page four, I just outline the flyby measurements that will be done
briefly. What we're doing is eight targeted flybys, and this means that
the trajectory of the Cassini spacecraft is designed, so that we make
these flybys in a particular altitude and a particular location over the
moon itself. These are special opportunities that we have to get very
high-resolution images and data from the other instruments; but even
besides these targeted flybys, there are many opportunities during the
74 orbits to look at the satellites from slightly more distant ranges
and then even from distant ranges, we can get good information, too.

As I said, the flyby of Phoebe, which is on rev zero, is a
2,000-kilometer flyby, and that's June 11^th^. Then we actually have
three targeted flybys of Enceladus because this is such a key target
because of its possible geologic activity and otherwise unique
appearance. We have three targeted flybys planned on rev four, rev 11,
and rev 61. Rev four is a 500-kilometer flyby, and that'll be on March
9^th^ of next year. Then we'll fly by Enceladus again on rev 11. That's
a 1,000-kilometer flyby on July 14^th^ of next year. Then we'll be at
Hyperion flying by at 1,000 kilometers on rev 15 next September. Then
we'll fly by Dione again at 1,000 kilometers in rev 16 next October.

Next November, we'll fly by Rhea at 500 kilometers. Then we'll have a
little break from the close satellite flybys because the geometry of the
trajectory basically is different in here for a while because the orbits
are more inclined. Until 2007 in September, then we'll fly by Iapetus at
1,000 kilometers. Then in 2008 in March, we'll fly by Enceladus for the
third time at 1,000 kilometers.

Then, as I said, in between the targeted flybys, we'll have plenty of
opportunities to look at all of the satellites at slightly more distant
ranges, and even more distant ranges. Observations are planned up to a
million kilometers or two.

As you can see from my list here, we are not planning targeted flybys of
all of the eight icy satellites just because it's impossible to do that
with the current tour, so we don't have any targeted flybys of Tethys or
Mimas, and we just have one of the others, but we'll have more distant
observations, and that should be very useful in particular compared to
what we have from Voyager because we have very limited coverage from
Voyager. And it's all fairly distant, so just with non-targeted
coverage, Cassini images and data of these icy satellites will really
help us to understand what's going on in these satellites.

Sort of broadly, some of the observations that we plan to do is, of
course, to take images with the camera. We just need to get better
coverage compared to Voyager to try to understand in particular the
geologic history of the moon by looking at craters, looking at other
features such as grooves, titanic features, if they exist, plains, any
mountains that might exist, and this will help geologists to understand
the geologic history and the internal activity, as it's evidenced on the
surface in the past on these moons.

Spectra and spectral images will be taken from the UV \[ultraviolet\]
all the way out through the long wavelength infrared. These will help us
to understand the composition of the surfaces, and that'll be kind of
the top surface layer, and also we'll be looking for any atmospheric
species. We don't expect any of these satellites to have anything other
than tenuous atmospheres that might be very -- they would be due
primarily to photochemistry to photons, but also charged particles
sputtering of the ice on the surface, then the gasses basically forming
exospheres around the moons.

The long wavelength infrared measurements will also help us to
understand the surface temperature, and so certainly, and this is in
particular the CIRS instrument, the Cassini infrared spectrometer. I
don't know if I have that right, the acronym, CIRS is going to be doing
measurements. They can measure both at daytime and nighttime on the
satellites, so it can measure day and night temperatures. This will
really help us to understand what's going on in the internal part of the
moons, and whether or not there's any activity happening, and hot spots
for instance.

Jane CIRS is Composite Infrared Spectrometer.

Amanda There's a radar on Cassini, and that will measure the surfaces of
the satellite to help constrain the bulk density of the surface layers,
and to also help us understand the relative cleanliness of the ice. In
other words, how much of the surface is pure ice, and how much is
material that's mixed in with the ice, contaminants, carbonaceous
material, etc.

Then radio science measurements will help us to understand the gravity
of the moons. It will help us to understand the mass and density of
these moons. That'll help us understand the internal structure, how well
segregated out the materials are.

Then we also have fields and particles instruments that will make
measurements in the vicinity of the moons when we do the close flybys,
to understand the effects of the moons on Saturn's magnetosphere and
vice versa, and whether or not there's any sort of magnetic field
associated with any of the satellites, and what the dust environment is
like.

Any questions thus far?

On the final slide, the general science questions and observations, and
goals and observations that we'll be making then is probably number one
on some people's lists anyway. What's the compositional makeup of the
icy satellites? We really need to understand much better what these
things are made out of. With the suite of instruments that Cassini has,
we'll really be able to get a good handle on this. We know that water
ice is there, as I said, but what else is there, and what does that tell
us about the histories of the satellites.

As I mentioned before, what are the affects of the E-ring on the
satellites and vice versa, in particular, Enceladus, Mimas, and Tethys?
We expect that we know that satellites orbiting a planet in a
magnetosphere are affected, primarily darkened by bombardment by the
charge particles in the magnetosphere. But it seems that from evidence
that we have---ground-based and Voyager observations\--it seems like the
satellites orbiting Saturn within the E-ring might actually be
brightened by E-ring material bombarding the satellites on either
hemisphere, so that will be looked into further. Then, of course, the
source of the E-ring, is it Enceladus? If it is Enceladus, is it due to
charged particles sputtering, or is it due to Enceladus losing material
through geologic activities?

Are any of the satellites currently geologically active? This is going
to be a prime question to be answered, and particularly in terms of
Enceladus.

What is the interior structure of the icy satellites, and this will
primarily be answered by radio science and tracking measurements that
will tell us again whether the moons are made up primarily of ice, what
the percentage of rock or non-ice material is within these satellites,
and how well segregated out the ice and rock materials are, and that
will tell us something about the thermal history of the moon.

Mimas and Tethys, as I mentioned before, both exhibit very large craters
that are large enough that they should have basically blown apart the
moons when the impacts occurred, and how is it that they did not? How is
it that they survived the impact that created these large craters? By
looking at the other features on the satellites, such as grooves and
other craters, and getting a better look at the large craters, we can
understand more about the history and the cratering history of the
satellites.

Then, of course, what is the source of the wispy streaks on Rhea and
Dione? They seem to be emplaced over craters, which means that they
would be newer than much of the cratering that has happened more recent
in history, but how did they get there? Such wispy streaks have not been
seen elsewhere in the solar system. These are very mysterious.

Then, of course, what is the source of Iapetus' mysterious albedo
dichotomy? Why in the world is that leading hemisphere so dark, whereas
the trailing hemisphere is sort of a normal brightness?

We'll actually be doing, we have the targeted flyby of Iapetus on rev
49. We have a close flyby of Enceladus, so at the end of this year.
It'll actually occur on December 31^st^. It's not as close as the
targeted flyby, but it will really help us to get a good first look at
Iapetus. It's really a perfect situation here because the flyby of
Iapetus at the end of this year will get us good looks at the opposite
side and with opposite lighting of the rev 49 flyby, so that'll be
excellent. We'll start learning about Iapetus relatively soon, rather
than having to wait until 2007, which is good.

Hyperion: Hyperion rotates chaotically in addition to looking battered
and beaten. Why does it rotate so chaotically? Is it relatively new to
the Saturn system, or did it survive an impact that knocked it out of
whack, basically, and it's still trying to adjust after that?
Particularly using images, we'll be able to look into that a little bit
more.

Then I highlight in red here, where did Phoebe come from? I highlight
this in red because it is coming up so close, and this will be our one
good opportunity to look at Phoebe. Because of the fact that Phoebe
orbits opposite to the other satellites, it orbits retrograde, and it
also has an extremely inclined orbit, it's orbit is inclined about 175
degrees, these are indications that Phoebe is a captured object.
Phoebe's appearance, the fact that it's so dark, it's spectrally bland.
It doesn't exhibit, other than water, it doesn't exhibit any absorption
features. It looks a lot like a C-type asteroid, which is a very
carbonaceous type asteroid, very dark, very spectrally bland. It's
possible that Phoebe is a captured object from the main asteroid belt.

It's possible that Phoebe is a captured object from a population of
bodies such as the Trojan asteroids of Jupiter's orbit, so those would
be both inside Saturn's orbit, but it's also possible that Phoebe was
captured from way out in the solar system, and that it could be a Kuiper
Belt Object or a KBO. If so, it's really exciting to be able to get so
close to Phoebe and to take such good measurements, because we have
obviously never been that far out in the solar system.

And so this would be kind of like sampling a Kuiper Belt Object without
having to go that far out. Kuiper Belt Objects are remnants from the
very early solar system, not very evolved at all, and so this will
really be an interesting find if it turns out to be a KBO. It won't be
easy to tell actually, but the fact that Phoebe is especially bland, but
also contains water is a strong indication that it didn't come from the
main asteroid belt or even from the Trojan population. Most of those
objects are spectrally redder than Phoebe, which is, as I said,
spectrally just bland and kind of black or gray.

We're all really looking forward to Phoebe, and hopefully you all will
hear about what we've found out and get to see the images soon after the
flyby, and we'll get to share in the excitement there, too.

Now this is all I've prepared here, and so I'm happy to take questions.

Jane I have a question. How many instruments during these flybys? There
won't be that much time to actually aim a whole lot of instruments on
each of the objects.

Amanda Right. Good question.

Jane How many? I can guess a couple of them, but I'm just wondering how
many actually get to gather some information.

Amanda During most of these targeted flybys, what we've done is the plus
or minus 12-hour period around the flyby is really the key time. That's
when inbound closest approach and outbound are really good
opportunities. So we've mostly planned out observations for about a day
around the flyby, and we've split up the time so that all instruments
who want to look and can get good science results out of such a flyby
will get a chance to look.

Now, the four remote sensing instruments, which are the camera, the
UVIS, the ultraviolet instrument, the VIMS, which is the visible to
infrared instrument, and the CIRS, which I mentioned already, which is
the long wavelength instrument, they're all aligned. So when we do
remote sensing observations, we'll get observations from all four of
those instruments.

If we want to do radio science measurements to measure the gravity of
the moon as we're flying by, then the ORS instruments, the remote
sensing ones, can't do their observations since we have to turn the
spacecraft a different direction. Similarly, if we want to do radar, we
need to turn the spacecraft, so that basically the large antenna on
Cassini is facing the moon. So the cameras and the other remote sensing
instruments can't observe, while we're doing radar or radio science, but
we try to split up each of the timelines fairly, so that everybody can
get to do their science and get good results out of it, so that we can
learn. The goal is to learn about all of these moons as much as we can,
and to learn about all aspects of them. It won't do us any good if we
have pretty pictures of the planet, but then can't understand what it's
made out of, for instance. Everybody needs to share, and everybody is
getting good information.

Jane That's great. Thanks.

Amanda Anybody else have any questions?

W One thing that's always bothered me about Dione, looking at the two
sides of Dione, you said we really didn't have a good feeling for it.
But not only does one side have these rays, and this is true, I think,
of Rhea and several of the other ones as well, but also very blue
looking, if you look at the colored ones, where one side looks kind of
gray and cratered, and the other one looks blue and very pretty, almost
more reminiscent of Ganymede. You really don't have any? Is this water?
It looks like it's got a lot more water on that trailing side, like it's
slamming in from the back from the magnetosphere ramming into it maybe.

Amanda I see what you're saying. Now, as far as I know, there's not real
color differences between the leading and trailing hemispheres of Dione
and Rhea. I know that one hemisphere is slightly brighter. I think on
Dione, and I should look this up, so I don't tell you something wrong.
But I think on Dione the leading hemisphere is a little bit brighter
than the trailing hemisphere, and that's kind of the typical situation,
because the trailing hemisphere is typically darkened by the
magnetosphere bombardment. But as far as I know, there aren't any color
variations. I wonder if the images that you're looking at where one side
looks bluer than the other are just due to maybe stretching of the image
or something like that.

W It may have been contrast enhancement a little bit, that's true, but
it sure looked like from the Voyager pictures, that the bright side was
very gray, and the dark side was very blue. Anyway, that's what it
looked like to me.

Amanda That's really interesting, but the thing on Dione, I think
there's about a 20% difference in albedo between the leading and
trailing hemisphere. So when you say the bright side, do you mean the
leading hemisphere?

W Yes. I mean the leading hemisphere is very cratered. The dark side was
smooth and blue. I know there's a Voyager picture that has it almost
edge on, so you can see the two sides in the same shot. It was very
dramatic to me, and I've always wondered. My class has always wanted to
be able to say why.

Amanda Certainly, everybody on Cassini will be looking for leading and
trailing asymmetry to help us to understand the exogenic processes,
because I was talking about the magnetosphere bombardment. There's
E-ring material that could be affecting Dione, and then what about these
wispy streaks. How did they get there, and why would there be streaks
like that if they're exogenically emplaced? Yes. Stay tuned.

There'll also be Dione ... later this year. I think it's in about
November. That's actually our second pretty good opportunity. Phoebe is
at 2,000 kilometers. Dione on rev B in about November is more distant,
but it's still a pretty good first look. I think it might be like
100,000 kilometers away, but stay tuned for those images because that'll
help us figure out what's going on there. And you can look for yourself
and see if you see color variations or not, too, because those Voyager
images, since they're lower resolution, sometimes it's hard to tell
what's real and what's not. I'm kind of looking through my stack of
papers here to see if I can jog my memory about Dione color variations,
but as far as I know, I don't recall hearing anything about that, but
that's a good question. Thank you.

M I had a question. Did you mention that there were two satellites in
retrograde orbit?

Amanda I didn't. All I said was that---

M Just one, just Phoebe?

Amanda Phoebe, and a bunch of the new satellites, the small ones that
have recently been found orbit in a retrograde motion.

M Which other one, other than Phoebe, is not tightly locked? Did you
mention that one?

Amanda Hyperion.

M Thanks.

Jane For those of you who are interested in timelines for news briefings
and press conferences and so forth, it looks like we're having one
Thursday, June 3^rd^, but I'm going to let Anita do the communication
with you just because she'll have the exact time. This will be kind of a
background press conference on orbit insertion. It won't necessarily be
about Phoebe, but it will be kind of the first of many press conferences
to do with the Cassini mission.

As far as the Phoebe flyby, we will be having an image release on
Saturday, June 12^th^. I don't think at this point that there's a press
conference planned on the 11^th^, but if there's anything, for all you
folks that want to know about these things, Anita will have her hand on
the pulse of that, and we'll get that information out to you.

Rosaly \[Lopes\] The press conference on Thursday is at 10:00 a.m.
Eastern Time.

Jane Right. It'll be on NASA TV. It'll be from NASA HQ with ESA and NASA
headquarters people, and it'll be 7:00 Pacific Time; but again all the
specifics, I know that Anita sends out a much more detailed announcement
to the museum folks, so we'll just make sure. That'll probably go out
tomorrow or something since today is the 1^st^ and Thursday is the
3^rd^. \[Bookmark
<http://www.nasa.gov/multimedia/nasatv/MM_NTV_Breaking.html> to check on
the NASA TV schedule\]

Any other questions for Amanda?

M I had one more question. Is our moon, is it darker, the leading edge?
Is the other end of the moon darker that we don't see? Did you make a
statement that it's bombarded by the magnetosphere that may darken the
leading edges?

Amanda That's a common -- I'm sorry if I didn't make myself clear on
that. It's common in systems such as Jupiter where the moons are
orbiting within the magnetosphere of the planet, so that's certainly the
case in Jupiter. It seems like it might be the case in Saturn too to a
certain extent, but no, not with our moon.

M Thank you.

Jane If we don't have any more questions, I think we can end the
telecon. The next one, I'm not sure who the speaker will be. It will be
on June 15^th^, and we'll probably have something out to you as soon as
we schedule out the next suite of speakers. Now that we're getting so
close to the mission, we'll kind of transition from talking about the
mission to talking about more specifics, I think.

Everybody fine with that? If you have any suggestions for talks that
you'd like to have, send them to Anita because we're always looking for
covering the topics that you'd like to hear about. With that, I think
I'll end the call.

M Thank you.

Jane You're welcome. Bye.