**FTS-NASA-VOICE stop on page 28/2/3 of wav file**

**January 31, 2006**

**1:00 p.m. CST**

Coordinator This is the operator, I'll start recording at this time. If
anybody does have any objections, you may disconnect. Ma'am you may
begin when you're ready.

Trina Okay, thank you very much. I would like to welcome everybody to
our first CHARM telecon of 2006. This is our first CHARM telecon by the
way that's also, not only is the guest speaker from overseas, he's
joining us from Germany, but we have two of our Saturn Observation
Campaign members are now international. We have somebody from Germany
and Ireland joining us today. So the CHARM telecons have gone
international.

Today we have joining us Dr. Sasha Kempf. He's with the *Cosmic Dust*
*Analyzer* and he'll be telling us today about the first results from
the dust detector onboard Cassini. We have two hours, is the full time,
but normally, Sasha, about one hour. Feel free to take as much time as
you'd like, but right around one hour would be good.

Sasha Yes, that's my intentions, too, since we have night right now in
Germany.

Trina Good boy. Go ahead.

(Audio cuts-out)

Sasha Okay, so I'm quite happy that you offered me the opportunity to
seduce you to the wonderful world of tiny dust grains. Actually, my
group at Heidelberg has quite some experience since we run the dust
detectors and we operated the dust detectors on the Galileo and Ulysses
spacecrafts. We had dust detectors on the Helios spacecraft and on
Cassini as well. We also provided assistance and participated in the
dust experiments on Stardust, on Rosetta and on the Giotto mission.

Okay if you'd just proceed to the first slide. So this picture shows you
the dust instrument before it was mounted on the spacecraft. This
so-called cosmic dust analyzer instrument was designed and built in
Germany. Part of the instruments were contributed by our colleagues in
England. They did some mass analyzer and we also carried tiny
sub-detectors piggy-back on the instrument that's the high rate
detector. This instrument was built by a group at the University of
Chicago.

The Cosmic Dust Detector of the Cassini spacecraft is capable to measure
the mass and the velocity of dust grains and quite an impressive march
range. So the tiniest particles we were capable to detect were out of a
few nanometers, while the biggest particle the instrument can reliably
detect is of the order of 50 microns to 100 microns even. The dust
velocity and the determination of space on impact ionization, this
principal; this basic detection principal was inherited from the
progenitors of this instrument on the Galileo and Ulysses spacecrafts.

In contrast to these detectors, the Cosmic Dust Analyzer is also capable
to determine, at least roughly, the chemical compositions, elementary
composition of the dust particles by means of an integrated
time-of-flight mass spectrometer. That's actually the first time that in
large sensitive areas, detector is capable to detect the.. to a ways to
give measures of the elementary composition of dust particles.

The instrument is also capable to determine, at least for the big
particles, the charge the particles carry on and this is achieved by
means of a grid sensor in front of the instrument. So the grids are
barely recognizable on the picture, however the function principal is
quite simple. The inner and the outer most grids are grounded, while the
two inner and inclined grids are attached to a charge amplifier. As soon
as a particle penetrated through the outermost grid, it starts to
influence a charge onto the interior grids. By means of that, we can
measure directly the charge on the grains.

You might ask what is great about knowing the charge on the grain. The
interesting thing is that, if you know the potential of the particles,
you can easily determine the mass of the particle. So this technique
provides you with an independent means of evaluating the particle mass.
Besides this, we can also extract from the shape of the charged signal,
information about the impact angle and the velocity of the grains. So
it's quite a well technique and with the Cosmic Dust Analyzer, they
actually demonstrate for the very first time, that this detection
principal works great for big dust particles. Okay?

The last capability I would like to mention is the high rate detector we
piggy-back on our instruments. The main detector, a so-called analyzer,
is capable to detect one particle per second at maximum. Although this
is sufficient for measurements in the interplanetary space, where we
usually detect one particle per week of the order of that and the inter
core of the E-Ring, the impact rate is much higher than that. So we
detected up to 100s impacts per second in this environment.

In order to do this, we have to high rate detector piggy-back that's in
foil detectors, particles penetrating the permanently polarized foils
and causing short charge signals and this charge signal can be counted
or it's counted by the detector. So this detector provides impacts
weights for particles larger than approximately a micron and this
instrument provides very useful information in the inter core of
Saturn's E-Ring.

Okay next slide. So now I would just like to explain a bit how we
actually derive the mass and the speed of the dust grains. The problem
is that the particles have quite large relative speeds with respect of
detector. So typical speeds are ranging between 5 kilometers per second
up to 100 kilometers per second and for stream particles it might be
even larger.

This is quite a challenge to determine the properties of such a
particle. The way we estimate the particle mass and the speed is by
means of the impact plus mass produced by the particles when hitting the
impact targets, indicated by the yellow color. When a particle hits the
impact targets at this speed, the particle is transformed into a mixture
of plasma, of impact plasma and of tiny ejecta.

The plasma is separated within an electric field and we are measuring or
we are analyzing the evolution of the temperate solution of the impact
plasma on various electrodes. We have electrodes attached to the impact
targets where we collect the electrons and we have charge sensitive
clips in front of the multiplier, where we collect the ions. Half of the
ions are capable to traverse through the ion grids and those ions are
collected at the multiplier and are finally forming the final flight
mass spectrum of the ions.

Next slide. It might be -- well it seems to be easy to understand why
the impact charge provides a measure of the impact mass and the impact
charge somehow relates to the number of atoms in the dust particle, it's
difficult to understand how we actually derive the speed of the striding
particle and I would like to take advantage to explain just a bit how
this actually works.

Now the sketch shows the spherical impact targets and the grain hitting
the target. We learned from that experiment that ejecta particles
produced by the impact are moving with approximately the same speed as
its parent particle. Since the anglular distribution of the ejecta is
identical for all dust impacts, we take advantage of the spherical
target by the circumstance that the time of the path links, the mean
path links of an ejecta, striking against the targets, is approximately
identical for all impactors. That means since we know the path links of
the ejector, this gives us a measure for the impact by analyzing the
time it takes the plasma to rise.

Since as long as ejector particles are hitting the impact target, new
plasma constituents are produced and the plasma charge is rising. When
the ejecta stops or hits the targets, the charge amplifier are
discharging again and so the time it takes the charge amplifier to rise
to its maximum value, is a measure for the speed. If you know the speed,
you can determine from the produced impact charge, the mass of the
particle.

This is the basic principal of our speed determination and we have an
accelerator facility at Heidelberg, which allows us to study dust
impacts or impacts by dust analogues in the speed range of five
kilometers per second up to let's say 70 kilometers per second and of
the mass range between 100 nanometers to let's say five or six microns.
We performed thousands of impact experiments and this provides us a
basis for quasi-empirical calibration of the right time dependence, and
of the impact charge dependence from the properties of the dust
particles.

The currency of the matter is approximately a factor of 1.6 from impact
speed and approximately a factor of six for the dust mass. So this might
seem quite huge but you should keep in mind that dust particles cover a
huge mass range and a huge speed range. So for the specific properties
of the dust populations, such instrument is really a very useful tool to
learn basically everything what's interesting about such particles.

Okay next slide. This slide shows you how a transmitted signal actually
looks like of a typical dust impact, that's an impact by an E-Ring
particle. The uppermost panel is the charge measured on the entrance
grid system and the second panel gives the charge measured on the small
inner-targets where we collect the plasma electrons. The next panel
gives the plasma electrons collected at the outer targets and the next
one The next channel gives the plasma ions collected on the ion grid and
apparently all three signals have similar rise times. The rise times,
which is market by the red color, gives us a measure of the impact speed
as mentioned.

In principal, all three signals provide an independent estimate for the
impact speed and for the mass of the impacting particle. The lowermost
panel shows the signal detected at the multiplier and for particles
hitting the inner-targets, we obtain useful time-of-flight mass spectrum
for particles hitting the outermost targets. The time-of-flight mass
spectrum does not really correspond to the time-of-flight signal since
the collimation of the ion started at the grid is too poor in order to
do this. Okay?

Yes that's it. So now I would like to talk about the major discovery we
did by the dust instrument on the Cassini Spacecraft, since we detected
streams of dust particles emerging from the Saturnian system. In order
to explain to you why this is great and why this is interesting and
stunning, I have to introduce you a bit to the history of the so-called
stream particles.

The next slide shows you a very old picture on a very old diagram. This
diagram shows the impact rate as detected by the Ulysses spacecraft and
Ulysses approached Jupiter in '92. Before this time, impact rates by
dust particles were quite boring, since the distribution of the dust
particles in the interplanetary space is at least smooth. I told you
before that the typical rate is of the order of one impact a week. So
being a dust scientist means that one needs to be very patient, however
when the instrument -- when the spacecraft approached Jupiter, the
colleagues detected quite something very different.

> They observed impact bursts approaching or arriving from the
> collimated source and they easily figured that the apparent location
> of the source on the sky was the position of Jupiter. Even a more
> stunning thing was -- a point was that the impact burst showed a clear
> periodicity and the periodicity was of the order of 27 days and of 14
> days. This is a magic number in planetary science and these reminds of
> the rotation periods of the Sun. However it really took the colleagues
> a couple of years to understand what they actually observed.
>
> You have to understand that the dust instruments on the Ulysses and
> Galileo Spacecraft did not transmit the impact signals itself to Earth
> but it just transmitted some characteristics of the impact signals.
> According to the characteristic of the impact signals, the colleagues
> thought that the mass of such particles is of the order -- or the size
> of such particles is of the order of microns. The speed of the order
> of 20 kilometers per second and this was very difficult to explain.
>
> Next slide: So the colleagues basically were faced by two major
> questions. What is the dust source within the Jovian system? So it was
> totally unclear, although everything pointed for Jupiter itself ,
> within in the system was quite the -- there are quite some arguments
> about this. The other important question was why are the dust streams
> outside the Jovian system -- the system periodic?
>
> Okay next slide: finally a couple of years after the discovery, a PHD
> student of Eberhard Grun found the proof that the particles actually
> -- or that most of the particles were actually produced by Jupiter's
> moon Io. This figure here shows you a plot -- a wonderful picture of
> this moon and on the left side you'll see a plume, due to the
> volcanism on this moon. This volcanism is the source of the particles
> and the acceleration mechanism is similar to the acceleration and
> speed of the accelerator and the particles were ejected into IO's
> plasma torus.
>
> The particles get charged and since Jupiter has quite a strong
> magnetic field, the particle starts to interact with the Jovian
> magnetic fields. Since Jupiter has a rotating magnetic or a rotating
> dipole field, the particles experience an electrostatic force in their
> -- in their frame of rest, accelerating them outwards, providing the
> particles are positively charged.
>
> As it turned out, by later analyzers, by Eberhard Grun, E. Horanyi,
> and Morfill, as they figured out, the magnetosphere of Jupiter
> actually works as a huge mass spectrometer. Since only particles in a
> quite narrow charge to mass range, it came from Jupiter's gravity. If
> the particles are too small, the particles tend to gyrate around the
> field lines of the dipole field as the particles just get stuck to
> Jupiter's magnetic field. Why when the particles are too large, they
> are not energetic enough to escape from Jupiter -- from Jupiter's
> gravity.
>
> The fact that the system acts as a big time-of-flight mass
> spectrometer, it gave also hints about the mass of the particles. To
> the surprise of the colleagues, it turned out that the particles need
> to be very, very tiny - of the order of perhaps ten nanometers. The
> particles also turned out to be very, very fast, of the order of 400
> kilometers per second. It was approximately identical to the solar
> wind speed.
>
> In order to understand why the particles shown outside the Jovian
> magnetosphere's pronounced periodicity, one needs to understand how
> the solar wind is structured.
>
> So on the next slide I show, kind of a reasoning why the magnetic
> field in planetary space has at least a narrow edge and spiral-like
> appearance close to ecliptic plane. The reason for that is that, the
> solar wind that's a thin energetic plasma is moving radially outwards
> from the sun and the conditions are such that the magnetic field lines
> are bound to be to the plasma volume elements moving radially
> outwards. Since the sun is rotating, the field lines finally just
> spiral up and approximately as the Earth orbits the angle between the
> field lines and the Earth orbit is of the order of 45 degrees and
> approximately50 degrees at the location of Jupiter, the field lines
> are basically parallel to the orbit of Jupiter.
>
> This spiral structure is the same as Parker spiral and was quite
> impressively confirmed by measurements by spacecrafts on various
> missions. However this not the reason why the particles show these
> periodicities.
>
> The next important fact is that the rotation axis of the sun is tilted
> with respect to the ecliptic plane and that means that's assuming a
> dipole field for half of the rotation periods the field lines are
> piercing the ecliptic plane from the above to the below. While for the
> other half of the rotation periods, it works the opposite and so we
> end with a scenario that approximately half of the spiral is
> characterized by field lines pointing outwards, while the other half
> of the spiral is characterized by field lines pointing inwards.
>
> So the consequence of that is that the interplanetary magnetic field
> shows some pronounced sector structure. However, there's a case and
> it's really a simple case. It's not always such that we have to deal
> with two sectors. There are also periods when we have to deal with
> four sectors and now assuming a particle traveling with quite some
> speed, quite slowly, radially away from the sun, then the energy
> detector for magnetic fields will show for the highest of rotation
> periods a field pointing upwards and while for the other half of the
> periods, the rotation periods, a field pointing down.
>
> This is probably the reason for the chaotic behavior of the dust
> streams but before I will explain this a bit how this works, I just
> have to introduce two other facts. It's also an important property of
> solar wind that's -- the speeds of solar winds change. This depends on
> the processes on the surface of the sun and so there are high-speed
> winds and low-speed winds. If a high-speed wind moves into a low-speed
> wind, a shock front comes into being and this finally resides into the
> formation of a so-called corotating interactive region that means
> that, as seen from the rotating Sun, the period of the shock front
> seems to be stationary.
>
> The important thing about this so-called CIR, the solar wind plasma is
> strongly compressed. So the wind speed is higher inside the CIR -- the
> shock region and the magnetic field is enhanced.
>
> Okay so what is the -- what has all this to do with the periodicities
> of the dust winds? First of all, the fact that we show a periodicity
> which remains on the sector structure of the interplanetary magnetic
> fields, immediately tells you that on the charge to mass ratio of the
> stream particles has to be quite large in order to allow them to
> interact strongly within the planetary magnetic fields. If this is the
> case and we assume a dust particle moving away from Jupiter towards
> the Sun, this was approximately the configuration on doing the Ulysses
> approach to Jupiter and for such a scenario, the B fields or the
> forces of the B fields, it's leading to enforce accelerating the
> particles upwards or downwards.
>
> So we end up with this dust trajectories oscillating around the
> ecliptic plane and whenever these kinds of warped dust streams is
> piercing through the ecliptic plane, the dust detector will see a
> stream - a stream of dust particles and this somehow roughly explains
> why the stream shows this peculiar behavior. However the explanation
> was not entirely satisfactory since although one could explain the
> basic mechanisms behind the formation of the streams, people had
> difficulties to explain why the streams are that short in time, why
> the duration of the streams was only three days and not modulated by
> synoidal function. Simulations by Zook and his colleagues finally
> demonstrated that only particles with speeds of 400 kilometers per
> second and sizes below 14 nanometers were capable to reach the dust
> detector for the configuration to the Ulysses approach and for the
> simulation to use the magnetic field data and solar wind data by the
> spacecraft.
>
> Now it's actually -- we actually use the known properties of the big
> mass spectrometer Jupiter in order to calibrate the dust instrument
> for such tiny grains and for such fast grains when the dust
> accelerator facility is not capable to accelerate particles of this
> size and this speed.
>
> Okay next slide: however perhaps two years ago or three years ago,
> Jupiter was assumed to be the only source of such streams since
> Jupiter has really strong magnetic fields and it's known volcanism .
> It just seems likely that Jupiter is the only candidate for streams.
> However Horyanii took a risk to propose that Saturn might also be a
> source of stream particles and we persuaded the Cassini Project to
> allow us to scan for such particles and we did this approximately half
> a year before Cassini started its tour around the planet itself. The
> most favorable spacecraft configurations detect stream particles or to
> detect any kind of collimated dust stream is to have the spacecraft
> perform a continuous roll.
>
> This will finally lead to -- or this allows us to scan with our quite
> large field of view through the streams and to determine the
> directionality of the streams reliably and since Cassini is not that
> well designed -- or the Cassini spacecraft is not capable to perform
> never ending rolls for very large long periods and be persuaded
> basically the project, to allow us to have the spacecraft rolling and
> for 30 days and believe it or not during these 30 days, we detected no
> stream particle at all.
>
> However when the spacecraft then started to maintain a fixed attitude
> to allow to the other teams to do a different kind of investigations,
> we observed the first stream of such particles and until the -- and
> until Cassini entered its orbit around Saturn, we detected 2,000 dust
> particles, stream particles. The stream of particles again showed a
> pronounced burst behavior, burst behavior. We also observed impact
> bursts of the order of three days and we also found that the intensity
> of the burst was increasing instead of decreasing the distance to
> Saturn. This all indicated strongly for Saturn being a source of
> stream particles as well.
>
> Next slide: so then we took advantage from the fact that we transmit
> the impact signals to Earth and just by looking onto the impact
> features on the electron collecting targets; we realized that the
> particles really were very, very fast. The first column shows a stream
> -- a particle we detected in the vicinity of Saturn and the red arrows
> indicate the rise time and risel time is really, really short.
>
> The next column shows the feature of the stream particle escaped from
> the Jovian system and the rise time is even a bit longer and longer
> rise times means slower particles. The right column shows the fastest
> impact we ever observed in the laboratory and the speed of this
> particle was of the order of 70 kilometers per second. From that we
> immediately concluded that the speeds of the particles, we observed
> when we approached Saturn, was of the order of at least 100 kilometers
> per second and then comparing with the signal of the Jovian stream
> particles, it's even possible that the particle -- or the signal is
> very comparable with impact speed of 400 kilometers per second.
>
> You we could also conclude from the impact signal that the particle
> needs to be tiny of the order of 20 nanometers or less. Okay now we
> made use of the fact that our colleagues studied very extensively how
> steam particles are accelerated within the magnetosphere of the
> planets. We applied their work to the conditions in the Saturnian
> System. The big difference between Saturnian System and the Jovian
> system is that the dipole fields of Saturn are stunningly well aligned
> with the rotation axis of the planet.
>
> The field is weaker; however the environment where the particles might
> acquire a positive charge by interaction with the plasmasphere of the
> planet is larger than for Jupiter. We learned from the analyzers that
> there are two regions where particles might end up as stream
> particles. On this plot, the escape speeds of the particle is shown as
> a color code on the X axis gives the initial position of the particle,
> which wants to become a stream particle and the Y-axis gives you the
> size of the radius of the particle. Since we will on the reduced -- we
> learned from the impact signals that the particles detected were of
> the order of at least 100 kilometers per second fast. Only the red
> colors are correspondent with possible candidates for stream particles
> and this was quite a surprise, since one region where stream particle
> might originate from it from is beyond the orbit of the icy moon
> Dione.
>
> This is indicated by the blue box, however particles starting at this
> environment, at this location, within the Saturnian System, need to be
> really, really tiny, of the order of two nanometers, which is
> ridiculously smaller. The other possible starting position of the
> stream particles on the outskirts of Saturn's A-Rings. This is really
> quite a surprise, since as you know, the A-Ring is composed of big
> bolders, of bigger bolders of ice bodies -- of icy bodies and this
> environment is not accessible for detailed studies by spacecrafts.
>
> So if the particles actually originated from the outskirts of the
> A-Ring, this provides us with the unique opportunity to study ring
> material from the main ring in detail.
>
> Okay next slides: so in order to figure whether the particle started
> from -- let's see an opposite position of Dione or the particles
> actually originated from the outskirts. We did basically quite the
> same as Zook did for the Jovian stream particles, we studied the
> motion of the particles in the planetary magnetic fields to watch
> Saturn and the plots at the bottom of the slide shows you trajectories
> of particles of different size. Started at the location of one of the
> big stream particle impacts we detected when we approached Saturn and
> apparently only the red and the black trajectory hit Saturn and red
> corresponds with ten nanometers and black corresponds with 28
> nanometers in size. While the tiny particle, the two nanometer meter,
> never hits Saturn.
>
> So the simulation excluded that at least the particles that we
> detected at large distances from Saturn originated from Dione's orbit.
> Those particles actually started from the outskirts of Saturn'sA-Ring.
> These are quite surprising results.
>
> Okay so this just summarizes what I explained to you, that at least
> the particles that we detected at large distances to the planet,
> originated from Saturn's A-Ring from the outskirt of the A-Ring and
> this allows us to study the -- at least some Ring material from the
> main rings by in situ technique and in this sense, the stream
> particles, the Saturn stream particles, are really the messengers from
> the main Ring.
>
> Okay next slide: so this plot shows you the mass spectra we obtained
> from ring particles. The lowermost panel shows the typical mass
> spectra of the Jovian stream particles we recorded when we did the
> Jupiter Flyby. As you can easily recognize the mass spectra of such --
> of Jovian stream particles are looking very different from the mass
> spectra above this particular Mass spectra and all of these Mass
> spectra are Mass spectra of Jovian steam particles. The Mass spectrum
> of Jovian particles is dominated by sodium and a PHD student of mine
> showed recently that, the best explanation for the composition of the
> Jovian particles is that those particles basically consist of sodium
> chloride, which allows to get some understanding about the processes
> going on in the volcanos of Io. However, these stream particles
> produced by Saturn are looking very different from that -- they always
> show a carbon feature, an oxygen feature, a weak sodium feature, which
> we could demonstrate as due to impurities on our impact target.
>
> It usually shows a silicon feature and that is quite interesting and
> it also shows a rhodium feature and rhodium that's the target material
> of the impact - that's the material to the impact target so the
> rhodium ion should show up in each mass spectra. By doing -- or just
> by co adding, see quite faint mass spectra of similar strength we
> realize that there are also tiny traces of SI02 and of perhaps of
> hydronium molecules formed on that's the ion formed by water ice.
>
> The next slide: then we realized from analyzing the mass spectrum
> aspect more carefully by the co-addition technique that we could
> separate the thousands of mass spectra, whatever you call it into four
> groups. There a four composition types. There is the silicatic type.
> This is a type which shows ions by -- silicone ions SIO2 plus ions and
> also ions formed of the target material and silicone. There's an
> alkali composition type and this type is characterized by showing
> lines of alkali. Elements of sodium and potassium and it can be shown
> that this is actually due to the impurities of -- on our targets. We
> also found clear in the -- sometimes about 10% of the impact spectra
> show indication of H3O+ and O+ ions. This might be due to the fact
> that the particles are covered by a thin ice mantle, but this might
> also be executed to just water vapor condensed on our impact targets
> due to the exhaust product of the main engine.
>
> However, the most important finding was actually that there is a line
> which can be executed to a cluster ion formed of the target material,
> rhodium and SI silicone and silicon atom or silicone ion and it's very
> difficult to form the cluster ion consisting or rhodium and silicon.
> We learned from that experiment that the -- well we studied a huge
> range or a quite impressive range of different mass of dust analogues.
> We learned from that, that the dominating species in the dust
> particles tends to form a cluster ion.
>
> This cluster ion is therefore an indicator that's for the most
> abundant specie in the dust particle. Since we found the clear
> indication for the cluster ion forms of rhodium and silicon, we
> actually found indications of the particles, the stream particles, are
> basically made of silicatic material and that's really a big surprise,
> since the main rings of Saturn as well as the -- and the faint rings
> of Saturn are composed of ice particles and when we started the tour,
> we studied the ice particles quite extensively and they are all
> basically all made of ice.
>
> It's difficult to explain why the stream particles are composed of
> silicate. However, there are a few points which at least give some
> hints why this is that case. First of all, there is an indication that
> there are silicatic impurities in the material of the main rings.
> Since the main rings appear to be a bit colored. Assuming silicatic
> impurity is one of the explanations for the ring color.
>
> We also found, when we started the tour, that also the ice particles
> composing, such as E-ring show tiny faint traces of silicates. So the
> best explanation we can offer right now is that basically all ice
> particles have tiny impurities by silicatic material. Perhaps the
> cores are due to where the condensation sits for the formation of the
> ice particles. Perhaps from the moon Enceladus and stream particles
> are just, you know the cause of the particles, which did not succeed
> to accrete substantial ice matter or the particles were produced
> between collisions of the ice parent bodies of the main rings and the
> cause of the collision, such material was set free and get charged and
> were exited outward and finally ended up as a stream particle.
>
> So we are still working on coming up with a really convincing
> explanation why these particles are composed of silicates but our mass
> spectra only allow this conclusion.
>
> The next slide: we also learned quite a big deal about the
> stream-like\... from the measurement. The data shown in this plot here
> are impacted data -- we recorded after Cassini started to tour around
> the planet. Whenever we on the spacecraft left the magnetosphere of
> the planets, we started to see stream particles and the interesting
> finding was that, outside the So we observed bursts and in between the
> burst impactors, we saw particles arising from approximately Saturn's
> position and the speed factor was approximately aligned with the ring
> plane of Saturn.
>
> This plot shows, at the upper-panel on the angle between the
> instrument boresight and the ring plane and the mid-panel shows the
> angle between of the instrument boresight and Saturn. The lowermost
> panel shows the impact rate. The grey structures are indicating the
> angular range scanned by the instrument. Basically each of these grey
> bars corresponds with an eight-hour spacecraft roll and during such a
> roll, the spacecraft performs about one rotation during half an hour.
>
> This allows us to determine directionality of the streams and the blue
> boxes indicate the directionality of the streams outside an impact
> burst and as I told you, outside an impact burst the directionality of
> the particle is parallel to the ring plane and pointing towards
> Saturn. However, whenever we observe the bursts, the directionality of
> the particle change rapidly to -- by very large angles and during the
> bursts the particles arrive from approximately 90 degrees above the
> ring plane, with respect to the ring plane.
>
> So the particles actually move on a bent trajectory and also the angle
> between the instrument boresight and Saturn changed quite
> significantly. The interesting finding was that, whenever we observed
> the burst we also found the spacecraft was traversing through CIR
> \[corotating interaction regions\] which I explained to you at the
> beginning of this talk. When the spacecraft is traversing in CIR -
> corotating interaction regions - the plasma conditions, the conditions
> within the solar wind changed dramatically. So there's increase in the
> impact speed in the solar wind speed, an increase in the magnetic
> field strength and there's an increase in the plasma density.
>
> Our best explanation is that whenever the spacecraft or the particle
> moves in such environments, the particle is charged up to higher
> charges. The particles experience a stronger force acting on the
> particle speed of the particle to the solar wind gets larger and so
> the increase of the speed of the particle actually leads to the impact
> burst. So it's not from the density of the particles which are
> increasing. It's the speed of the particles relative to the spacecraft
> that's increasing.
>
> Since the fields strengths are larger inside the CIR, the particle
> trajectories are more bent and this leads to the deviation from the --
> from its original trajectory. So the measurements we did outside the
> magnetosphere, after the Cassini started its tour, basically answer
> the question, what is actually the mechanism behind the formation of
> dust streams. It's actually -- the interaction of the particles with
> CIRs and this is quite consistent also with the measurement, the
> current measurements by Ulysses spacecraft at the outer planets from
> the university of Mexico City analyzed the Ulysses data starting from
> '92 and he found also quite a impressive correlation between CIR's
> crossings and the duration of the burst and the directionality of the
> burst.
>
> Next slide: Here the structure is the same finding again and for
> longer periods. So this plot covers approximately 50 days and the
> green color indicates crossings of or traversals of the CIR by the
> spacecraft and the lowermost panel shows the field strengths, which is
> the indicator for CIR structure and that's quite a reasonable
> correlation between the change of directionality and the end of
> traversal of CIR. Now we are capable to predict or to tell the
> magnetic of the MAPS people, are people dealing with fields and
> particles, when the spacecraft traverses through a solar wind stream.
> So we are actually quite a sensitive -- well we turned out to be quite
> a sensitive detector for structures and solar winds.
>
> However -- next slide on -- I'll summarize again what I tried to
> explain, that inside the Saturn's magnetosphere -- since thin sheets
> of radially escaping grains are formed and these sheets are warped by
> the action of with the solar wind and then whatever these particles
> are traversing through in solar wind stream, the particles experience
> a strong exhilaration and finally forming an impact burst or an impact
> stream or -- as seen by the dust instruments.
>
> Okay but the next plot shows quite a stunning result. We found that
> it's not only the interaction with the CIR, which are forming an
> impact burst. We also found that from time to time we saw an impact
> burst but it didn't and we didn't see a change in the directionality
> of this grain. It turned out that whenever this happened, the
> spacecraft was traversing through plasma, which was due to a coronal
> mass ejection event and although we have no explanation why this leads
> to this behavior of some particles, we found quite a stunning
> coincidence between such events and the impact rate. This is basically
> all I can tell you about the stream particles and if you are really
> excited about what we will learn on doing the remaining two years of
> the Cassini's tour in particular, since the spacecraft is now starting
> to move on a slightly inclined orbit, at the end of the tour we will
> move highly inclined orbits, which allows us to come up -- as with
> basically a three dimensional picture of the stream particles emerging
> from the system and this will allow us, hopefully to give you a couple
> of years the full picture of the these interesting particles. I thank
> you for you attention.

Trina Okay are there any questions?

W I'd like to ask a question.

Trina Go ahead.

Deirdre Deirdre Kelleghan here - SOC member in Ireland. My question is
about the high-rate detector. It's plated with gold and it receives a
high-velocity frequent impacts. So does a soft metal like gold withstand
all these impacts?

Sasha Oh I haven't heard the question so\....

W Okay.

Sasha Yes I had a better connection, I hadn't heard you.

Deirdre Will I repeat the question?

Sasha Yes.

Deirdre Yes my question is about the high-rate detector. It's gold
plated and it receives high-velocity frequent impacts. So how does a
soft metal like gold withstand all these impacts?

Sasha The material, the high-rate detector is not gold.

Deirdre Not gold?

Sasha The material of the high-rate detector is so-called PBDF, so the
PBDF is an abbreviation for a quite a complicated name for organic
materials. The particularity of this material is that it is thin foil.
One foil is 28 microns in thickness and the other foil has about 6
microns in thickness. At the back of the foils, is a metal film in order
to support the foil and the property of this foil is as follows: the
foil is permanently polarized and when the particle punches the hole
into the foil, it temporarily depolarizes the materials. This
depolarization leads to change of the competence of the foil and this
change of the competence is measured or is detected by charge amplifiers
attached to the foil.

This short burst or this short peak of the charge signal can be used to
detect the impact. They also made use of the fact that the amount of
charge produced by the impactor is also at least roughly a function of
the mass and the speed of the particle, as you can imagine of the impact
energy. That's why the high-rate detector -- the charge signal of the
high-rate detector is attached to four chage sensitive comparators. We
count the peaks within four charge ranges and this allows us to come up
at least with a rough picture of the impact rate of the function of the
particle mass.

So provided you know the impact speed of the particles and that's quite
often the case when you are in a planetary ring, particles are moving in
Keplerian orbits and so you know with an occurancy of about a factor of
1.4. The speed of the particle, you get the measure for the impact for
this charge and by means of that you know the mass. This detector is
only sensitive to big particles. Stream particles cannot be detected by
such a detector.

(Overlapping voices)

Deirdre Can I ask you -- I have another question just connected to.. Are
there plans to compare the cosmic dust samples from the CDA with the
samples from Stardust 's Comet Wild 2?

Sasha Yes of course, we are happy to be guided by our colleagues. The
problem here is that the dust, the Stardust Mission collected particles
in the interplanetary space and this would be quite a challenge to
identify such particles within the array aerogel since they estimated
about 30 to 40 particles of this origin.

They collected particles at the comet and the cometary material is very
different from the material we deal with in the Saturnian system, since
the Saturnian system basically, all dust particles are made of water ice
and of course water ice particles, even if they're were water ice
particles in the vicinity of the comet such particles bounce away from
the aerogel. However, we learned from the analyzers of such particles
quite a lot how to interpret our cruise data so we got - we recorded
three or four good mass spectra of interplanetary particles and the mass
spectra of such particles indicated silicated material as well. That's
actually not a big surprise and we are very happy that the return
mission succeeded and we will definitely learn from that.

Deirdre Thank you.

Sasha I just -- to be honest, mass resolution of our mass spectrometer
is about 50, so we cannot come up as an isotopic analyzers of the
particles. So we just can collect on the principal type of the particle.
If its a carbon particle, it's an organic particle, and it's a silicated
particle or an ice particle. We cannot do much more.

Deirdre Thank you very much.

Sasha You're welcome.

Trina Are there any other questions? So, Sasha what are you looking
forward to in the next two years of the mission?

Sasha Well of course we hope that there are more close flybys at the icy
moons. We got exciting results at the icy moons. We found that Enceladus
is -- or Enceladus has an ice volcanism going on its surface and so we
all have big interest to have as many close flybys of the icy moons as
possible. We also -- our basic desire is to map the particle properties
within Saturn's E-ring in order to understand the dynamics of such a
planetary ring. Since the E-rRing is the biggest planetary ring of the
Solar System, the E-ring is a good analogue by the way for a pre-disk
around a young star.

So what learned from such measurements will be of quite some importance
for some of my colleagues as well. We also want to map the composition
of the particle within the ring and by means of that; we want to learn
something about the transport processes within the ring. As you perhaps
all ready realize, all these goals by the CDA team are based on big data
sets is based on statistic analyzers. So we are -- we hope that we will
be able to collect data within -- for as long as possible. The more
data, the better and this is what we actually are hoping to achieve
during the mission.

As I told you before, we are also quite eager to study the dust
environment around the planets when we are at higher latitudes, since
this is actually the first time that a spacecraft moves ...? the ring
plane or the ecliptic plane around the planets and studies the
conditions at high latitudes and this would allow us to understand the
stream particle phenomenon or even unexpected new phenomena much better.

Homer I have a question, if I may ask please.

Trina Sure go ahead.

Homer This is Homer and I'm in South Carolina and it sure is good to
talk with you, speak with you. I spent some time in Heidelberg and also
Darmstadt - beautiful country. I have a couple of questions if I may
ask. I was concerned about that you said the charge of the particles
help determine the speed. You've also talked about the composition. Does
the charge of the particles hit -- do you also determine the
composition?

Sasha You mean the impact charge we collect at the target?

Homer Yes, sir.

Sasha Yes in principal yes. What we actually do is to separate the
impact plasma in a strong field. So in front of the inner-target there
is some grits. So the distance between the grits and the target is
approximately three millimeters and there's a strong separating field.
By means of that, the ions acquire approximately the same starting speed
and the same energy and this allows us to do a time-of-flight mass
analysis of the ions collected at the multiplier.

You are right, the likelihood to produce an ion from the specie, within
the particle. It's not only a function of the abundance of this ion,
within the particle it's also a function of the composition of the
particle itself. It's a function of the speed of the impacting particle
and that's the case us about our measurements. It's not necessarily so
that, when a specie does not show up in the mass spectrum, that the
specie is not there. However if a specie shows up in the mass spectrum,
the specie's in the particle and for the analyzer of the stream
particles, we exploited the fact that they are cluster ions and cluster
ions are a good indicator for the abundance of such atoms in the
particle. Besides that, the analyzers of such a mass spectrum is really
complicated. All in-situ mass spectrometers flown on spacecrafts are
suffering from this limitation, since it's turned out to be impossible
to get rid of the\.... The particles always have these huge relative
speeds with respect of the spacecraft. So whatever you do, if you do in
situ analysis of a particle on the spacecraft, you either have to
collect the particle in the collector as Stardust did, or you have to
analyze the impact level. That's what we do.

Homer \...Thank you very much. My second question I had really is I
believe you mentioned that dust particles in Jupiter are moving towards
the Sun. I can understand that but the question I guess I'm having in my
mind is the Earth magnetosphere is preventing most of this from entering
into the Earth and be collected here. I was thinking about the
International Space Station. That would be a good location also to do
some studies on the dust particles but I'm so excited the dust particles
from Saturn and also very interested in the CME events having affect on
the dust particles at Saturn. Thank you very much and I appreciate any
help.

Sasha Yes just to comment to this. We started to see stream particles,
Jovian stream particles when we left the asteroid belt. This was
basically the case for all spacecraft which detected stream particles.
Stream particles from Jupiter, were now detected by Jupiter, Galileo and
Cassini. Right now Ulysses is at very high latitudes and when Ulysses
approached Jupiter during the last year, it again detected stream
particles high-latitude. It's not very likely that such particles will
actually be detected at the space station. The distance is too large and
at this distance, probably the dynamics of the particles is all ready
entirely randomized by the interaction with the interplanetary magnetic
fields. So there's actually no need to worry about such particles, so
they can only be detected outside the asteroid belt.

M I have a question.

Sasha Sure.

M I'd also like to say I've very much enjoyed visiting the University of
Heidelberg and the Schloss as well. This is Pete Goldie from San
Francisco. Can you tell when your detector is just chance upon a
cometary stream of dust particles? I guess a number of those attracted
to the gravity of Saturn.

Sasha Well a former PHD student of my group just told me when he
analyzed the cruise data of the Cassini detector that he probably found
an indication that Cassini traversed through a cometary trail in 2003.
However, we detected 14 particles between Jupiter and Saturn and 6 of
them are attributed -- although they are attributed to a cometary trail
and so this gives you a measure how difficult is to detect such a
phenomenon and the problem with Saturn is that Saturn is actually the
dustiest place in the Solar System perhaps except during the rush hour
at L.A. and there's that much dust that you really have difficulties to
distinguish between particles from exterior sources moving inside the
Saturnian system and the ring particles itself.

So we detect right now of the order of a thousand to two thousand
impacts per day and so since there are that many particles, they
basically arrive from any direction. The only way to distinguish between
the particles -- the various particle sources right now is by means of
their mass spectra. Up until now, we haven't found a good indication for
a particle in the interplanetary space detected inside Saturnian System.
This is entirely due to statistics and this finding is very consistent
with the estimates by Jeff Cuzzi and Paul Estrada about the iflux into
the Saturnian System.

However there is a unique and exciting possibility to determine the flux
of particles into Saturnian System by studying the dust environment of
icy moons. Since the icy moons are that big, they have very large
sensitive area for dust particles and dust particles hitting the surface
of such moons are producing more dust particles which finally form a
dust cloud around the moon. By measuring the number density in the dust
clouds to get an estimation of the external impact of flux, this is a
quite interesting technique to determine this important number, since
the colleagues, which are interested into the age of the main rings.
They want to know how much dust particles per century are moving into
the Saturnian System and changing the compositions by means of that, to
change the composition of the main rings. This gives them the handle to
estimate the age of the rings.

P. Goldie Thank you.

Trina Do we have any other questions?

Phil Phil Evans in Palmdale.

Trina Go ahead.

Phil Yes I'm just curious, looking at the spectra in these stream
particles, there's a couple fairly strong lines of rhodium at least
looking at it from the Earth here is a relatively rare metallic element.
Is that something that we would expect to normally find in that part of
the solar system? If not, is there an explanation?

Sasha We definitely expect rhodium to show up in our mass spectra in the
targets, the impact target is made of rhodium and we chose this material
carefully. Since rhodium is not a likely candidate for cosmic silicate ,
for cosmic particles and rhodium is an inert material. So rhodium does
not tend to form molecules with other possible contaminants. We used
this material for the impact target and this gives us also the
possibility to calibrate the mass scale of such impact, since we know
that rhodium needs to show up and we know the mass of rhodium and by
means of that we can perform a better calibration.

Most of the other time-of-flight mass spectrometer flown on spacecraft
used silver as an impact target. Silver is also a great material and
silver has the two isotope with almost identical abundance, with can
also be used quite nicely for calibrating the mass spectra but we chose
rhodium and that's why it shows up in all the mass spectra.

Phil Thank you.

Trina Are there any other questions. Okay well I'd like to thank you
very much, Sasha for joining us today. We know it's very late there in
Germany and we really appreciate you taking the time. We've learned a
lot today and hope to see you back here in a year or two when you can
tell us about the rest of the exciting discoveries that CDA is making
out at Saturn.

Sasha I'm happy to do this. Thank you very much for your attention.

Trina For the rest of everyone, we are sort of canvassing people to ask
for their ideas, for what talks they'd like to hear from the CHARM
telecom in 2006. I'm trying to line-up some talks on Titan's atmosphere.
We've had a lot of work done on the project recently, trying to
understand the variability of Titan's atmosphere and that would probably
be an interesting talk.

I've lined-up a UVIS occultation talk and a couple of Rings talk. I was
wondering if people would be interested in a more detailed spacecraft
talk. I know that we've talked a lot here about the science results from
the mission but I was thinking a year or a year and a half into this
that maybe a very detailed spacecraft talk about the capabilities of the
spacecraft. How we control the spacecrafts to all the engineering
sub-systems. Would that be of interest to this group or I'm just asking
because I have a whole bunch of you on the line right now.

W I'd think that would be a great idea for the spacecraft details.

M Yes I adore that.

Trina Okay.

W Yes the speaker here in Ireland.

Trina It sounds good and then are there any ideas that people are
interested in learning about. Another idea I was thinking of was
following up with the Huygens Probe folks a year after their mission.

W Yes that would be great too.

Trina Okay.

M Can we have perhaps a session on, what are the ideas being thrown
around for the extended tour?

Trina Oh an extended tour, yes because we're just starting to do that
work now.

W Hey, Trina?

Trina Yes.

W Is it an idea to also talk about the new reference trajectory or is
that the wrong audience for that?

Trina That's probably a little too detailed but I mean we can ask. I
mean right now, because of the difference in Titan's altitude, we're
having to change the trajectory slightly. Is that a topic of interest to
this group? I would not think so but I think it would be more
interesting for this group to talk to the Titan scientists, who are
working on understanding Titan's atmosphere.

W Okay.

Trina If there's any comments from the group at large? Okay any other
ideas? We've basically stepped through most of the instruments but we
have a few still to go. We would need a really good VIMS talk but I'm
hoping to get that as part of a VIMS Ring science talk. So we basically
hit all the instruments. Is there any other topic that people are
sitting around wondering?

W Will there be anymore close Flybys of Enceladus or anything
interesting like that?

Trina We do have another close Flyby of Enceladus but it happens later
in the mission, it happens at 2007. We have certainly had a lot of
interesting science results from the Enceladus flybys of last year and
I'm hoping to get an icy satellite talk in too in the works for this
year. Also Hyperion is very interesting.

W I'm sure it is yes, definitely\....

M I have a question, if I may ask. This might not be interesting for a
study but I was watching the -- looking at the Saturn's magnetosphere
and I noticed that the shape of the magnetopause is different from that
of Earth. It has a pointed -- almost an arrow-shaped towards the solar
wind, as compared to a rounded affect on the Earth's magnetosphere. I
was just wondering and maybe I could find this on the Internet, looking
for it on one of the websites but I just wondered if anyone's thought
about that.

Marcia Trina, this is Marcia.

Trina Marcia \[Burton\].

Marcia Yes hello.

Trina Yes\....

(Voice fades off)

Marcia Burton I work on the magnetometer, I'm here at JPL and yes there
are people at Imperial College that are actually modeling the shape of
Saturn magnetopause and bow shock and doing comparisons with Earth. I
don't know if that would be a full talk but maybe if you get one of
those people to present their results.

Trina We did have a nice MAG talk in the middle of last year. We might
be able to go back to that presentation and take a look to see if it was
addressed.

(Poor audio)

Marcia Yes well I think I probably gave it, I don't know. I mean it's
just a matter of time, while we accumulate a number of bow shock and
magnetopause crossings and then people model that. In general, Saturn's
magnetosphere tends to be blunter than the Earth's. I think the new
results are kind of upholding that finding. That finding was from
earlier spacecrafts such as Voyager but I think Cassini is pretty
consistent with that. We could get somebody, if people are interested in
magnetosphere topics, we could get somebody from Imperial College.

(Overlapping voices)

Trina Actually we had somebody, I'm just drawing a blank on who it was.
It was on of the younger scientists.

Marcia \...Oh it was? okay.

Trina Who was that?

Marcia I don't know; I didn't hear it.

Trina Oh gosh, it was -- boy I'm starting to lose my mind. Are there any
other topics that people are interested in because I'm trying to set up
the whole year up front?

M Personally I'd like to see another one on some of the spiral density
waves of the Rings. I think -- I forgot who did a -- six or nine months
ago but I wish there was a little bit more on that because I still -- I
still can't really present that in my presentations based on what was
shown there so..

(Overlapping voices)

Trina Okay yes we had -- Jeff Cuzzi gave a brief talk in the July, I
think, telecom, because it was the one-year anniversary. I'm sure we'll
have another one of those also by the way. I'm sure we're setting-up for
July or June to have the two-year anniversary. Sort of a summary of our
second year in orbit - will be one of the talks that we'll arrange.

Richard This is Richard Manning calling.

Trina Yes?

Richard My Son Rob had a really interesting session with the Cassini
Spacecraft's computer system and it might be interesting to figure out
how he decided to enable all of these different experiments to happen
within the computer system that they devised for the Cassini. Sort of a
how-to or how they did it type of discussion.

Trina Oh how they did it, sort of a -- you know building the spacecraft,
retrospective kind of thing.

Richard Yes especially when you consider all of the variety of
experiments that they were trying to accomplish and how do you fit all
of those, not only physically but electronically and digitally within
the spacecraft itself?

Trina Okay also another talk that might be interesting is how do we
operate the spacecraft day-to-day, sort of in practical terms. What do
we do here at the laboratory and around the world with our scientists,
to put together a sequence and get it up to the spacecraft?

Richard Yes.

Trina Okay and that -- a day in the life of the Cassini Spacecraft. We
might make it a month because we do sequences on about a month basis.
Okay any other ideas?

M Yes, Trina this is a -- I'd like to know more about how each -- how
the different outreach activities are working. What's been working,
what's been not working very well and how -- kind of how they all
interplay and dovetail through one another.

Trina Okay we should certainly be able to do that. We have a lot of the
Outreach people that participate in the CHARM every month. Okay well if
you have any other ideas please send it to the
charm_leads@cdsa.jpl.nasa.gov and I don't know what the talk will be for
February. I'm still trying to line-up the first few talks of the year
but everybody have a terrific month and we'll see you next time.

M Thank you very much.

W Okay thanks very much bye.

M Bye.

M Thank you very much.