NASA's Jet Propulsion Laboratory
presents the von Karman lecture a series
of talks by scientists and engineers who
are exploring our planet our solar
system and all that lies beyond
Wow we pack the house tonight how's
everybody doing excellent well thank you
all very much for again coming to attend
these wonderful lectures we very much
appreciate them the Cassini mission a
cooperative undertaking by NASA and the
European at Italian Space Agency's has
revolutionized our understanding of
Saturn its rings an amazing assortment
of moons and the planets dynamic dynamic
magnetic environment the astonishing
discoveries continue to this day and we
can't wait to see what happens when
Cassini repeatedly dives between the
innermost ring and the top of Saturn's
atmosphere during its final six months
starting in April 2017 before finally
plunging into Saturn's atmosphere in
September tonight we have two guests who
will present highlights expectations
challenges and the promise of Cassini's
final year dr. Earl Mays is the manager
of the Cassini program a veteran of 32
years at JPL he began his career working
on the navigation and engineering teams
for the Galileo mission to Jupiter
after Galileo's final earth flyby he
transferred to Cassini as the spacecraft
operations manager and then deputy
project manager he left the project for
eight years to hold management positions
in guidance navigation and control and
avionics then returned to Cassini as the
program manager in January 2013 dr.
Linda spill ker is the Cassini project
scientist and a co-investigator on the
Cassini composite infrared spectrometer
team and has worked on Cassini since
1988 since joining JPL almost 40 years
ago her first and only out of college
job by the way she has worked on the
Voyager project the Cassini project and
conducted independent research on the
origin and evolution of planetary ring
systems she also supports proposals and
concept studies studies for new missions
to the outer planets she enjoys yoga and
hiking especially through her favorite
Park Yosemite and is married with three
daughters and five grandchildren so up
first tonight perhaps one of the coolest
grandmother's ever dr. Linda Spiller
thanks mark that was a great
introduction and as Mark indicated
Cassini has truly rewritten whole text
books on the Saturn system from the
planet itself to the complex ring system
to these just amazing and astonishing
moons that come in all shapes and sizes
and then the great magnetic field that
surrounds the planet itself now I'm
going to cover some of the highlights of
Cassini's journey in the Saturn system
her 12-year voyage around Saturn and
then Earl is going to talk about the
grand finale
those last precious orbits of Cassini
with truly unique science essentially
like a brand-new mission and then those
final moments with Cassini now if you
look at the picture behind me this is
one of my very favorite montages from
Cassini and as a ring scientist you can
probably guess why in this you can see
all of the major rings of the Saturn
system and it's a unique geometry the
planet itself is covering up the Sun
allowing Ksenia sensitive cameras and
detectors to mosaic this backlit view
it's kind of like looking through you
know a dusty windshield or something and
these particles brighten up and you can
see them so what you see is the planet
itself then the main ring system that
faint ring just outside the main ring
system is the G ring and that beautiful
blue ring is Saturn's earring and it's
created by tiny icy particles that come
from the South Pole of Enceladus that go
on to form a ring that fills in celle
this is orbit these particles even go
all the way out to the orbit of Titan
one of the distant moons at Saturn now
if you look closely at Saturn you'll
notice that there's a white ring around
the planet and this is where the
sunlight is refracted through the top of
the atmosphere into your eyes and it's
so beautiful because when you look at
this ring around Saturn you're seeing
every sunrise and sunset on the planet
at the very same time and you're looking
at the dark side of Saturn and yet
something is lighting up the night
side and what's lighting up the night
side is actually light coming from
Saturn's rings so the sunlight hits the
Rings on one side and it then reflects
on to the night side of Saturn so just
one of the many many incredible images
that have come back from the Cassini
mission now I'm often asked why do we
explore space why do we send robotic
emissaries out like Cassini what are
some of the grand questions we hope to
answer and Cassini addresses two of
those these are something that we're in
a survey for planetary science we do
these once every 10 years
so the first grand question is are we
alone in the universe
has life originated somewhere other than
earth perhaps in our own solar system
and how did life originate on the earth
another grand question is how did the
solar system and the earth within it
come to be how is it evolving and where
is it headed by studying the planets in
our solar system we can learn about how
our solar system formed how the planets
may have migrated as the system evolved
and where we might be headed and it's a
good analogy for other systems around
other stars now here's the and I just
want to go back briefly here and show
you these are the eight planets in our
solar system Saturn is the sixth planet
out from the Sun it's the second largest
planet and it takes 30 years to circle
the Sun a single time
now Saturn is indeed huge it's the
second largest planet the this shows the
earth and the moon to scale and the
distance in between them and so you can
see that Saturn would just fit in
between the Earth and the moon and if
the earth were a tiny marble it would
take 764 earths to fill up the volume of
Saturn so truly a giant planet and what
you're seeing are just cloud tops Saturn
doesn't have a solid surface like the
earth it's all clouds mostly hydrogen
and helium and maybe a tiny rocky core
about the size of the earth in the
center now here's an overview of the
Cassini mission Cassini was launched
from the earth and I
1997 we used gravity assist to a Venus
1 flyby of the earth one of Jupiter and
arriving at Saturn in July of 2004 now
originally Cassini was funded for a
four-year prime mission and by the end
of the prime mission we found we had
enough fuel and a healthy spacecraft
that we actually had two extended
missions the equinoxes where the Sun was
shining right on Saturn's equator edge
on to the Rings and then a seven-year
solstice mission and northern summer
solstice at Saturn will be in May of
2017 and the mission will last just past
that ending in September of 2017 and you
can see there at the end in the green
box what we could call the proximal
orbits or grand-finale orbits and
they're shown above highlighted in this
box and this whole mission is shown
against the 30-year orbital period for
Saturn so by the end of the Cassini
mission at the end of 13 years we'll
have been in orbit in the Saturn system
for almost two seasons they change very
very slowly at Saturn and right now
Cassini is almost to that green box
we're going up an inclination and we're
getting ready for our final set of
orbits this is another view of the
Cassini mission by year you can look
across the top bar shows the number of
orbits and the shapes of those orbits
then you can see that by the end of the
mission we'll have a hundred and
twenty-seven flybys of the giant moon
Titan and Titan is like a giant rocket
engine every time we fly by Titan it's
like expending almost as much fuel as we
spent to go into orbit for Saturn orbit
insertion and we get great views of this
very interesting body as well we've had
23 flybys of Enceladus and in the prime
mission the first four years we had
three we discovered in solidus was so
interesting that it reshaped our
thinking for the extended mission and we
added 20 more flybys of Enceladus we
have 15 flybys of the other icy
satellites and then you can see the
seasons changing from northern winter to
northern summer over the course of the
Cassini mission
and then of course those proximal or
grand-finale orbits at the end and early
we'll be talking about those in more
detail this is a Cassini orbiter and the
Huygens probe you can see a great model
a quarter scale model over in the corner
of the Cassini spacecraft Cassini she's
about 22 feet tall that antenna at the
top is about 13 feet in diameter it's
comparable to the Voyager antennae you
can see over in this other spacecraft
here you can see people for reference
and fully fueled Cassini weighed six
tons and about half of that was fuel
that we spent about a third of that just
to go into orbit around Saturn the
Huygens probe was provided by the
European Space Agency and it was
specifically designed with the goal of
being thrust into Saturn and Titan's
atmosphere parachuting down and landing
on the surface of Titan now Cassini
isn't just a spacecraft that's made up
of metal and bolts and bits and pieces
but this is kind of my view of Cassini I
see Cassini is made up of all the people
that are on her team the scientists the
engineers the support staff and in a way
Cassini represents all of their hopes
and dreams all of the things that we
want to accomplish and there are times
when I almost picture myself there with
Cassini in the Saturn system as we get
back some of these wonderful images or
spectra or data of these incredible
places and I almost feel like I'm right
there looking through Cassini's eyes and
watching as she collects her data and
feel very proud to be a part of this
incredible mission now on to some of the
science this is the tiny moon Enceladus
and so this is only three hundred miles
across
Enceladus would fit between Los Angeles
and San Francisco so it's a very tiny
moon and yet a very interesting one when
we saw it with Voyager we saw a very
bright icy surface generally in the
solar system something bright means that
it's young you haven't had a chance to
build up the pollution from the
micrometeoroid bombardment and also
you'll notice as you go south there are
very few craters in fact
there are no craters at the South Pole
of Enceladus and you can see for
tiger-stripe fractures that's our
nickname for those blueish features
there
Alexandria Baghdad Cairo and Damascus so
have very interesting names and those
fractures were something that were in
darkness when the Voyager spacecraft
flew through the Saturn system so we
didn't know we were they were there
until we had the Cassini spacecraft now
our first flyby in July of 2005 our
magnetometer team said there's something
interesting going on with Enceladus the
magnetic field lines from Saturn don't
go down to the icy surface like they
normally went for a body frozen solid
instead it kind of reminds us of a comet
those field lines are standing off
there's something going on in the
southern hemisphere and so they
encouraged us we had a thousand
kilometer flyby the first time they said
go closer we can really get a lot better
data so we went closer and also trained
our other instruments on Enceladus and
we found here this is with the composite
infrared spectrometer the team that I
work with they found that the Enceladus
South Pole was hot it was about a
hundred degrees hotter than the rest of
Enceladus
and if Enceladus were frozen solid it
was much harder than it should be and in
looking more closely that heat lined up
with those tiger stripe like fractures
so this excess heat was a puzzle we had
a an occultation of a star going behind
this region we looked at these tiger
stripes in more detail on the various
flybys here's a tiger stripe it's about
a mile or so across typically about a
hundred miles wide and it's just this
large gash four of them in the South
Pole you can almost see what looks like
a frosted side on the left-hand side
there we wondered what could be going on
with these tiger stripes we also had
images and the answer it was very clear
there are Jets of material water vapor
water ice particles shooting out of
these tiger stripe like fractures here's
another view of those Jets coming out
just going all different directions
continuously going off ever since
Cassini arrived at Saturn and we've been
watching and cell it is so not only do
you get water vapor and water ice coming
out you have things like ammonia
methane carbon dioxide you have many of
the key ingredients that you might need
to find life coming out of these jets on
Enceladus and part of our the goal of
our flybys is actually to fly through
this material and in October we came
within 50 kilometres of Enceladus
surface right under the South Pole and
it gave us a chance to essentially taste
and smell those particles figure out
what they were made of and try and
figure out the activity inside of
Enceladus here's another view of those
icy Jets this is a backlit view similar
to what you saw earlier in the Saturn
image you can see the sunlight shining
through each of these jets and we found
in the particles that some of those were
salty it says there's a global ocean
underneath and syllabuses icy crust and
it's as though there were frozen sea
spray and they contain sodium and
potassium salts and we know the pH of
the ocean very similar to the oceans
here on the earth so very interesting
finding in the particle data this is an
interesting view this is another
Enceladus this is a fountain at
Versailles and their gardens there and
this particular in solidus is as a Greek
giant and he had a run-in with his grand
niece Athena and he lost
and so his fate was to be forever buried
under Mount Etna so I think here he's
protesting a bit with this giant 82 foot
high geyser of water who knew in the
1670s that Enceladus would actually kind
of be doing something like this now
here's an artist's concept of what might
be going on you have the liquid water
ocean underneath the ice the crust and
that carbon dioxide might be sort of
like shaking up a champagne bottle you
pop the cork and perhaps that's the
energy that's there to raise that water
vapor and icy particles to send them
continuously into space now most of the
material falls back onto the surface of
Enceladus the particles are too large
and they just there they fall back and
it's like it's snowing if you could
stand near a tiger stripe underneath
that you could put out your hands and it
would be like it would be snowing on
Enceladus maybe a future
vacation destination you know who knows
but some of the tiniest grains escape
into space and there would go on to form
that very beautiful blue earring that
you saw in the first image if you look
carefully in this image you can see this
tiny black dot that's Enceladus
underneath it is the bright plume of
material coming out and you can see
wisps and tendrils of those icy
particles going out to form the e-ring
now the earring particles are so tiny
that they spread throughout the system
and if you turned off and sell it as as
Jets it might only take a hundred or 200
years until the earring has gone
completely so that's like sort of a clue
we see the earring we know the Jets are
going off at Enceladus this is just an
artist concept of the inside of
Enceladus
we know it's differentiated that just
means it's separated into a rocky core a
global ocean and an icy crust we've also
found that in looking at some of our
particle data there are tiny grains of
silica we call these nano silica grains
what's unique about them is these nano
silica grains can only form in water
that's near boiling so we think happens
is that the water goes into the rocky
core of Enceladus it's heated up there
Enceladus is kept warm by a resonance
with another mooned Ione that's
essentially just pumping heat energy
into it and once that water is heated up
it absorbs these minerals in particular
silica when the silica comes back out
through these hydrothermal vents hits
the cold water those minerals condense
into tiny particles then those particles
are frozen into the particles that go
out into space that Cassini can measure
so this is an indication that there's a
possibility of hydrothermal vents on the
sea floor of Enceladus now if we look at
our own planet we have the same kind of
hydrothermal vents on the seafloor of
the earth this is along the mid-oceanic
ridge in the Atlantic Ocean it's very
very deep no sunlight penetrates to that
depth this is illuminated from basically
the headlight of the submarine that's
looking at this particular event and
here you have silica and
Tass you and other minerals that
condense in the cold water on the
Earth's sea floor forming what looks
like smoke and these are what is known
as white smokers on the earth there's
also something along the seat depending
on the composition there are black
smokers as well and they're more iron
rich so a different composition what's
interesting is here in the deep cold
ocean where you have no sunlight the
only heat energy and nutrients are
what's coming out of these vents you
find an amazing array of life you find
tiny crabs you find tube worms you find
little tiny animals all sorts of life in
an island around these hydrothermal
vents and so we wonder if we can find
life in our own ocean perhaps might
there be life in the ocean of Enceladus
so some of the factors that life might
exist there include a global salty ocean
pH very similar to our own we know it's
long lived a global ocean probably
formed at the same time as Enceladus
there's organics coming from the ocean
to the limits of the instruments we have
to detect them carbon chains up to c6 c7
they're probably even longer but that's
the cutoff of the instruments what we
can measure heat energy coming from the
hydrothermal vents on the seafloor and
best of all for Enceladus it's giving us
free samples and it turns out when we
launched Cassini we had no idea that
there'd be these jets or vents coming
out of Enceladus so we didn't carry the
instruments that we would have needed to
look for amino acids and fatty acids and
long-chain molecules that could tell us
that life is there so this just means
that this is a wonderful destination
this ocean world to go back to Enceladus
and to keep exploring and answer the
question are we alone in the universe or
perhaps might there be life in Enceladus
is ocean now another very interesting
moon is Saturn's moon Titan Titan is
about ten times bigger than Enceladus
and fact Titan is about the size of the
planet Mercury if Titan had formed
anywhere else in the solar system Titan
would be a planet instead of a moon
now this was the Voyager view of Titan
and we just saw this hazy world and we
couldn't see through to the surface so
after the Voyager flybys in the 1980s a
group of scientists got together and
said you know we really need to start
thinking about going back and it was
both US and European scientists and that
was basically the birth of the idea for
what became the Cassini mission now
Titan has a very dense atmosphere it's
made mostly of nitrogen very similar to
the Earth's atmosphere no oxygen but it
has methane in its atmosphere and
methane is really the key at Titan
because you see methane plays the role
at Titan that water place here on the
earth the methane can be a gas it can be
a liquid it can form clouds it can rain
onto the surface of Titan that the
temperature of Titan surface is just
right to have be at the triple point
where you could have a liquid a solid or
a gas for methane now the methane is
also part of the problem with the smog
on Titan because you see some of the
methane goes high up in the atmosphere
the solar photons the UV breaks the
methane apart they grow into larger and
larger chains of molecules and that
forms haze very similar to the smog that
we have here on the earth when the
particles grow that large enough they
actually fall down onto the surface of
Titan now the Huygens probe was spelled
specifically to let go through the
atmosphere land on the surface and
reveal the surface for the first time
and so this is an artist concept at the
Huygens probe you can see it coming in
it was released from Cassini on December
25th 2004 and entered into the
atmosphere and landed on Titan on
January 15th of 2005 so the heat shield
basically ablated away carrying away the
heat energy and once the probe had
slowed down enough then the parachute
could come out and for the next two and
a half hours the Huygens probe floated
gently down to the surface of Titan
softly landed on the surface and
returned data for another half hour and
Cassini was the relay so as the Huygens
probe was floating down Cassini was
flying overhead collecting the data
then to send back to the earth for the
Hawaiians probe so really an amazing
mission with Huygens we didn't know what
we'd find would we land in an ocean
global ocean of methane that was a
possibility so we built the Huygens
probe to float at least for a few
minutes but it turns out that we didn't
have to worry about landing in an ocean
instead here's the view that we had with
the cameras we measured not only the
pressure temperature and composition of
Titan's atmosphere on the way down but
the cameras took these pictures and
about 60 kilometers above the surface
the haze finally started to clear and we
got a view of the surface and we started
to see what looked like mountains as we
went on our way down and in fact the
Huygens probe became the very first
object to land in the outer solar system
land on a body the furthest away from
anything we've had previously here's a
view of the surface you can see on the
leftmost panel these are rounded icy
pebbles that tells us that fluid has
flowed in this region probably we landed
in what was the equivalent of a dry
lakebed
we had a lamp you can see the spot for
the lamp here to give us an idea what
the color might be of the surface and
you can see the icy pebbles here and
here's a really neat comparison this is
from our own moon here's a footprint of
one of the Apollo astronauts you can see
the astronaut and a little flag up here
so this is sort of the same perspective
view that we had on Titan and we also
could see all of these channels
indicating that indeed methane was
flowing and we found a world that was
remarkably like the earth in so many
ways in fact there were lakes and seas
that Tynes North Pole lakes of methane
in fact this Lake Ligeia moiré is about
50 percent larger than Lake Superior
it's about 500 feet deep which is about
the depth of the Great Lakes as well so
there's a tremendous volume of methane
on the surface of Titan and in fact if
you could gather up all of that methane
knowing the depth of the sea is a
typical depth you'd have ten times more
hydrocarbons than all of the reservoirs
we have here on the earth
so if only we could build a pipeline big
enough to go from Titan all
to the earth our problems would be
solved but there's just tremendous
amount of hydrocarbons on the surface
and you can see the channels flowing
into that particular sea dunes those
particles that form high in the
atmosphere fall down form these long
dark linear dunes that wrap around the
equator of Titan those so those long
dark linear features there's also
mountains this is a mountain color-coded
with height mountains can be as high as
a kilometer or so on Titan and we think
perhaps in this case you look at it it
might have even been an ancient krile
volcano perhaps water mixed with ammonia
flowed out on the surface of Titan and
perhaps with that water perhaps came the
methane there's not enough methane and
Titan's atmosphere to have lasted from
the time Titan formed so there needs to
be some internal source periodically
releasing methane otherwise once the
methane gets divided up in the upper
atmosphere the atmosphere would collapse
so it's there's some source of that
methane clouds we've seen lots of clouds
as to the colorized cloud we've seen
lots of clouds and and weather on Titan
we even saw a rainstorm a methane
rainstorm on Titan the darker and the
surface and then we watched with time as
the surface slowly dried up then here's
a view of the dry riverbeds now in
looking at these images what you see
here though the lakes and the dunes are
taken at radar wavelengths radar
wavelengths are very good at penetrating
through the haze and so we really have
gotten tremendous views of a large
portion of Titan's surface this view is
what you would see with the cameras you
can see hints of the lakes in the north
pole at polar region what we did is we
carried near-infrared filters
specifically designed to go through and
penetrate the haze and look at those one
of the things in the beginning we didn't
know for sure is in those Lakes was that
truly a liquid or some kind of a goo or
something what really was it and we were
trying to figure out how do we find out
if it's a liquid without going there
landing in the lake and finding out and
it turns out we have another instrument
the visual and infrared mapping
spectrometer looking at near-infrared
wavelengths and it five microns it found
a bright spot called a specular
election if you have sunlight coming in
at an angle reflecting off a liquid
surface it comes out at the same angle
and if Cassini is looking at that angle
they'll see a bright spot over the lake
if you ever been on an airplane
sometimes if you're looking out the
afternoon window as you go across a lake
or a river
you might notice there's this bright
spot that pops up when you go over a
liquid and that's a specular reflection
I just want to say a little bit about
the Rings the Rings have very simple
names A through G just we keep naming
them with other letters as more of the
rings are discovered the main rings of
Saturn Saturn is off to your left the
main rings that you would see through a
telescope or the a ring the Cassini
division which is the astronomer that
discovered Cassini division and for
which our mission is named the B ring
which is the most optically thick ring
and then the C ring and they're also
additional rings just shown in the
bottom panel here's the innermost D ring
it's very very faint you've got it the
tenuous very narrow F ring just outside
then here you have the e ring going all
the way out to Titan and it turns out
there's one more ring in the Saturn
system and this ring wasn't discovered
by Cassini but it was discovered by
ground-based observers and it has
created by Phoebe so there's a ring the
Phoebe ring that actually comes in to
the Saturn system as well now here's a
Cassini view of the rings of Saturn
they're made mostly of water ice and on
average they're only thirty feet thick
so incredibly narrow for the hundreds of
thousands of kilometres that they span
from end to end there's tremendous
amount of detailed structure there some
of it we understand is the interactions
with the tiny moons just outside but so
much of that structure we still have no
idea what's causing that incredible
structure we do know that there are two
moons it actually orbit in the Rings
there's one that orbits in the Anki gap
named Daphna sand other one named pan
these two moons keep their gaps open so
we know that you know that information
about the Rings and here's a nice view
of the very dark very very tenuous D
ring now this is the lit side of the
Rings what you would see through a
telescope but there's also another side
to the Rings in this movie I was taken
by kiss
basically you're writing along as
Cassini is plunging down through the
ring plane you can see the a ring
Cassini division and B ring every once
in a while you'll see a tiny moon go by
there's Titan you can see it's it's much
larger now you get to see the other side
the dark side of the Rings the side
where the Sun isn't shining in this case
the B ring blocks out all the sunlight
the Cassini division is very bright the
earring is bright and cans just see a
hint of the bright c ray so the Rings
look very different and that's the
advantage if you go to a place like
Saturn you can see the Rings on both
they're lit and they're unlit sides now
Christina also had a rare opportunity at
Equinox in fact we just had our autumn
equinox that just I think very early
this morning and that's when the Sun
shines directly on the equator and in
this case it shines on the Rings edge-on
and that's important because with the
Sun edged on to the Rings essentially
you've turned the sunlight off for the
Rings and this mosaic taken by Cassini
what we've had to do here is increase
the brightness of the Rings by about a
factor of 20 so you could even see them
because they're only now illuminated by
Saturn shine and around on the dark side
of the Rings where it's darkens in
before Saturn's shadow we've had to
increase the contrast by about a factor
of 60 now you here you can see the
narrow F ring but it's slightly tilted
so it can still catch the sunlight even
around Equinox now a 30 foot thick rings
what's unique is you can look for
anything that sticks up above or below
the ring so if you're bigger than 30
feet in size there's a chance you'll
cast a shadow and we can see you so
we're looking for objects with Cassini
that would be larger and would cast
shadows and so I'm just going to show
you an image now this is the outer edge
of this ring the beii ring and it
stretched out and lo and behold we found
shadows lots of them turns out that the
outer edge of the Bering is held in
place by a resonance with one of
Saturn's moons and it looks like some of
the largest particles or maybe they form
and grow right there at the edge of the
B ring now some of these are probably a
kilometer or two in size casting very
long shadows but there are hundreds of
across the Bering almost looking like
little mountains along the B ring and a
good analogy is if you wanted to say
find the pyramids if you're looking out
from the Space Station if you looked
around noon they'd be hard to see
against their sandy background but if
you look near dawn or dusk the
equivalent of Equinix they would cast
long shadows making them much easier to
pick out against the sandy background so
in the same way Cassini used this to
look for structures and we found a
number of different structures like this
that would cast shadows in the ring so
very as a ring scientist a very exciting
time to be looking at Saturn's rings and
finally here's a very interesting
discovery for the Rings it turns out
that there is a feature this feature is
about twelve hundred kilometers long ten
kilometers or so wide indicating that
there's a tiny object two or three
kilometers in size creating this feature
this feature is right at the edge of the
a ring so as discovered in 2013 its
Discoverer Carl Murray discovered it on
his mother-in-law's birthday so he
nicknamed it Peggy after her so this
tiny object that's here creating this
feature Peggy
we've been watching for her ever since
she comes and goes we're wondering will
she break free of the Rings and become a
moon in her own right or will she be
torn apart and jostled by the other
particles in the Rings and disappear so
so far she's still there we're gonna
keep watching for her through the end of
the Cassini mission we're kind of
rooting for her by now because she's
she's been around for a few years moving
on to Saturn one very interesting event
happened at Saturn a giant storm
developed toward the end of 2010 the
storm grew so huge it was a giant vortex
and that vortex world off this huge tail
the tail of the storm wrapped itself
around the planet there was another
vortex on the other end kind of like a
hurricane when these two vortices merged
that marked the end of the storm a
tremendous amount of energy was released
in this storm at Saturn and typically
these storms happen about once every 30
years and so this
the fifth time we've seen a giant storm
like this at Saturn but what was unique
is this storm was early it had only been
20 years since the last storm and so it
came early so Cassini could get a good
view of it and watch it and so we
watched it as did ground-based observers
it lasted about nine months and started
to fade now this is in the visible if
you look toward the near infrared you
see deeper into the atmosphere the
colors in this view if it's white or
yellow that's high up in the atmosphere
Green is also high up that's the center
of the storm and then the yellow then
the oranges and the Reds are looking
deeper so we're basically getting a
profile of what that storm looked like
and how those clouds behaved and we can
model that and perhaps have it use it as
an analogy to storms in the Earth's
atmosphere now looking at some of the
longest infrared wavelengths the thermal
infrared turns out that the storm was in
the lower atmosphere of Saturn the
troposphere but when those two spots
merged it released a tremendous amount
of energy kind of like a giant burp and
here up in the stratosphere is a large
very hot feature and this feature
persisted for a couple of years and has
slowly cooled so very a very dynamic and
active Saturn at least in that time
period
now Saturn has a very interesting
feature at its North Pole
here's that feature you're looking right
down at the North Pole of Saturn that
features a six-sided jet stream called
the hexagon the Voyager spacecraft first
saw this feature in the 1980s and it was
still here when Cassini arrived you can
see the pinkish clouds this is a false
color view
rotating around and they go faster the
closer you get directly to the North
Pole and at the North Pole there's a
giant hurricane and this hurricane is
about 50 times larger than a typical
earth hurricane blowing about 340 miles
an hour and finally before I pass it
over to Earle this is a view of the
changing seasons in fact Saturn's shadow
on the Rings you can think of as a giant
sundial and this picture taken back in
April of 2016 you can see that the ring
the shadow of Saturn
just past the Cassini division at
solstice that shadow will pull in until
it's about in the middle of the B ring
and so as that shadow pulls in so will
Cassini's time shorten that Saturn with
that I'd like to turn it over to Earl to
talk about the grand finale
so how does Cassini follow that how do I
follow that I want to go first next time
you know one of the things about
Cassini's that always Trump's itself you
know as we keep finding you know one
year we announced a subsurface ocean the
next step next year we announced a
global ocean so it keeps building and
building and building and then you look
at the last 12 years and how do we do
something even more spectacular in our
final year well I'm going to show you at
least the potential for that but before
we do that I want to just a little bit
of a backup here I want to go to the end
this is September 14th 2017 it's about
Oh two o'clock in the afternoon here in
Pasadena and Cassini has just wrapped up
a 30 30 hour or so observing session the
recorders are packed full of images and
data kills in particles data and so now
it's time for Cassini to turn back to
earth and begin to play those back so
this is a high speed slow speed version
of the last of these periods so
Cassini's going to be working with this
for about 10 hours DSN is gonna be
receiving all this data we are going to
be streaming these back and as soon as
we see them you'll see them some
spectacular images of the poles and of
the Rings as we come in and then when
the SS ours the solid state recorders
are empty be about 10 hours Cassini is
going to reconfigure for the periapsis
here at Saturn on let me try so we've
done that 292 times over the last seven
years periapsis at Saturn is it's pretty
routine but not this one this one is
absolutely unique because it's casitas
last three days before this event
Cassini had a close encounter with Titan
Titan gave it a little gravitational
nudge and that nudge has pretty much
sealed Cassini's fate as a matter of
fact it's not coming out of this
periapsis it's moved to periapsis the
closest approach distance inside the
capture radius of the Saturn's
atmosphere and so Cassini this one is
going to reconfigure itself so that
doesn't put the data on the recorders
it's gonna put everything out
pipe as quick as it can so the minute
you see now it's going to start to turn
colors here's Cassini reconfigures
Cassini is going to go into the
atmosphere and every second of this data
is going to be coming back to the earth
and unfortunately Cassini is going to be
going 77,000 miles per hour you can get
around the earth in about 20 minutes at
that speed so what's going to happen
it's going to happen very very fast we
are going to have the every piece of
data streaming back down we're going to
be sampling the atmosphere and trying to
answer some of the fundamental questions
about Cassini a Saturn's atmosphere but
it's not going to be very fast it ought
to be very long at 77,000 miles per hour
Cassini is going to be going in with its
antenna pointing to the earth but the
atmosphere is going to quickly overpower
its ability to point it just doesn't
have that kind of control it's going to
push it off and then we'll lose comma it
essentially would disappear from our
monitors and about three or four minutes
later that speed and the density of
Saturn's atmosphere will vaporize
Cassini and it is over one of the most
spectacular missions ever to leave Earth
a discovery machine like you will never
see and it's gonna be done so why are
you doing that the first thing what do
you I did you guys ask anybody's
permission to take something that is
rewritten science programs redirected
NASA programs and recontour missions you
ask you're just going to destroy it let
me give you a try to explain why we
think that's a good idea
in order to do that I got to go back a
little ways so back to 2009 Linda told
you about the prime mission and the
extended missions we got to Saturn in
2004 right we had a four year mission
but we didn't have any in there was no
endgame planned but we got to the end of
that mission realized we had a
incredibly good spacecraft lots of
propellant so we went for another two
years about midway through that second
mission 2009 said 'jesus all subsystems
are great this system is wonderful we've
got a lot of gas in the tank let's do
something else so what
what's next and we actually got a lot of
study study you know there it's there's
a lot of opportunities at this point
with all the subsystems going we could
have left Saturn we could have gone off
to the Centaur asteroids and turn
ourselves into reconfigured repurpose
Cassini as an asteroid mission we could
have believe it or not left Saturn and
gone to Jupiter or gone out to Uranus
Uranus or gone out to Neptune now I
gotta say this was a 40-year cruise so
you know I mean it would have been long
cruise but you know what look whatever
Voyager is it could it was possible we
could have gone back to Jupiter that
actually is an image we took on our way
out and we could have gone back and it's
you know the same set of resources on
Jupiter Saturn Uranus is also a
possibility or more shattered well you
know this is kind of a no-brainer I mean
we had barely scratched the surface
Saturn is just incredible you couldn't
have asked for a more dynamic
environment you've got the rings you've
got the planet you've got the icy
satellites
you've got Titan and Enceladus little
prebiotic worlds on their own and
Cassini is still unwrapping this so it's
really not hard to figure okay we got to
stay so you know I'll jump to the chase
real quick now we're not going there nah
we're not going there we're gonna stay
but there's a catch if you want to stay
at Saturn there's some rules and they
are we call up planetary protection but
the real essence of this is you've got
to protect Saturday ocean worlds Cassini
is essentially a victim of her own
discoveries you my apologies to the Oak
Ridge Boys but you can you can visit but
you can't stay so you've got to make
sure that if you stay in the Saturn
system there is no possibility of a
crash landing on Enceladus or Titan
Cassini is room temperature inside if
there are little microbes in there that
don't mind a vacuum they can list lasts
forever
while we are we're running essentially
at about 72 degrees inside their
spacecraft is so going and taking
some of our Earth's microbes or spores
onto Enceladus in particular where we
know there's water warm water would just
be absolutely unacceptable so you guys
can stay but you got to be careful about
what you do about Titan and Enceladus so
with that in mind you say well how are
we going to do that we could stay and
goo big long orbits you know stay way
outside the orbits of the cell that's
way outside in orbits of Titan but guess
where all the science is it's down there
with Titan whose eldest so we want to do
explore these guys but we want the same
time remain safe so we go to the
trajectory designers we've got a fair
bit of propellant we've got good
subsystems what can you guys do for us
we want to be able to stay inside Souder
system we want to explore all the icy
satellites we want to explore the rings
of Saturn but we want to still remain
safe for these two you know incredible
worlds so what these guys gave us with
the Solstice mission trajectory this
started in 2010 and this is a trajectory
designers masterpiece it's a lot of
squiggly lines but each of those is in
orbit and every time that orbit changes
shape it's because Titan move this as
Linda said we get essentially a Saturn
orbit insertion velocity change every
time a flyby Titan so you want to go up
you to fly under Titan it pulls you up
you want to go in you go to the right go
to the left and we take you all over the
system so what we did what the
trajectories I understood they took
these orbits that you stayed very flat
in Saturn's plane that's by the way that
center there in the middle very flat and
then you could stay and do all the
satellite interrogation you want you
could go very inclined very looping
orbits to do magnetic fields and to do
the poles and the Rings and as a bonus
to all of that those this is the first
six years of this mission the mission
that Linda just reported you also get
this this is the last year of the
mission and this is unfortunately at the
end the demise of Cassini as I described
just a few moments ago but on the way in
we have an entirely new
something we have never done before
we're gonna flirt with the outsides of
the rings and then we're gonna go go
diving deep in between Saturn and the
Rings and I'll show you a little bit
more about that just to just to show off
some here because these things are just
phenomenal the key orbital
characteristics of this final set of
orbits which we call the F ring and
proximal z' you'll hear some of the
flight team call them Firpo sounds more
like a dog food than a that a real
acronym but really that they're Ephrem
orbits and what we're now calling the
grand finale 42 short period orbits each
of these orbits lasts about a week the
flight team is going to be running
around like they have never you've never
seen 20 of them are going to be oops
I've hit the wrong button sorry I have
it again there we go 20 of them are
going to be just outside the F ring
right this is the outermost ring here
Titan is going to be this and both these
essentially running in tight and right
out here twenty of these outside with
great coverage of the poles and the
Rings and then another tight and flyby
is going to move us in to the gap
between the innermost D ring and the
outermost edges of Saturn's atmosphere
22 of those the periapsis is going to be
in what we call a 20 20 400 kilometer
clear zone between them essentially
Scylla and Charybdis we've got their
dust on the left and we've got the
Saturn on the right we've got to
navigate in between next slide is I
think a look at the view from Earth not
only are these things phenomenal from
their proximity to the system the
geometry is also phenomenal because if
you look at what happens here these
orbits go behind the Rings in behind
Saturn almost every one of them from the
view from Earth provides what we called
awful tation not only do we have
instruments that can photograph and
sample we also have instruments that can
send a very very precisely tuned radio
signal to earth and passing that signal
through the Rings and the atmosphere can
tell us a tremendous amount about their
internal structure the opportunities
here are absolutely phenomenal and we
and we by the way Saturn
alleged by never if you recall back to
lip Linda's picture never opening up the
Rings more than they are right now
so essentially be passing the wage right
through it's an absolutely unique and
spectacular opportunity this again is
just to show a little bit of what
happens at the periapsis
you can see you don't quite see the F
ring on this illustration but it is
right so I've done it again there we go
we have a these rings here the F ring is
actually coming out right here we have
about an eight thousand kilometer gap
there but there's extended dust and if
you look at the F ring i actually more
terrified about that that i'm about the
the gap because of these tendrils that
keep coming off the F ring but
nevertheless that's where we're going
and then again do you see the proximity
of these periapsis here inside the four
would call the proximal the grand finale
this is again just kind of showing off
but it's here is a is a straight and a
flattened out version these are the
rings Saturn here's the F ring up here
and here is Saturn's atmosphere down
here Saturn yeah atmosphere Saturn
doesn't have a surface or if it does
it's way down in there so what we called
the surface is essentially the one one
bar level essentially the pressure of
sea level so that's what we're calling
the surface of Saturn so here are
graphically each of our periapsis so
we're flirting around in this safe
little gap between the F ring dust I've
done again we'll get to that the between
the the Rings here incredibly precise
navigation to stay between the dust
hazards between the F ring and the Janus
and Epimetheus rings here then the Titan
flyby that brings us down in here and
then we stay very carefully and very
precisely within the gap between
Saturn's atmosphere and the dust until
our final flyby here now I should point
out there a couple that are actually
flirting with this and we're going to do
some things here to keep ourselves safe
because they're a little bit more more
dicey than the
others okay so what's it like to be on
Cassini when we're doing this I've
already stolen my thunder on this flight
a couple of times
imagine you're just sitting on on the
prow of Cassini going through this is
seven seconds of Terror every seven days
for seven plus two months so Mars has
got their seven minutes we got seven
seconds every seven weeks and this is
exactly and this is the white-knuckle
time for us now we won't know because
most of the time going through here we
don't want to have the spacecraft
talking to us we want it to be doing
science so we'll find out if we've
survived these ring plane crossings much
later in the game but that's the way it
goes you want to get the science you
don't want to find out if you're going
to make it so this is going to happen 22
times every Tuesday I believe but I
could be wrong about it so the fight
team there many of them here are we are
going to be very very busy
so the science
I love the engineering of all of this
but really the engineering is all in it
because of the science and this is this
is just some of the unique things you've
seen what what Linda showed already and
it is phenomenal and we're going to
continue to do some more of that even
while we're here but these are
opportunities that we will never ever
get any other time
Saturn internal structure magnetic
fields and gravity will actually be able
to determine for the first time the mass
of the Rings by flying in between the
Rings and Saturn we can get a sense of
where they you know which ones which and
that tells us something very fundamental
believe it or not we don't know how old
the Rings are they could be a couple
hundred million years they could be a
billion years there's a big argument
about that and and very very intelligent
people on both sides of the case we
think we can help with with some of
these measurements yeah Saturn's
atmosphere and the innermost ring
particles and the highest resolution
ever ring observations themselves when
we went in orbit 2004 we went over the
Rings but they were not lit we got the
dark side so now we can finally see
these rings fully illuminated by the Sun
and as I showed that picture earlier
this Saturn's cooperating
incredibly good phase angle with the Sun
and also we're gonna a trade are the
rings you saw the radar images of Titan
we're gonna try to do the same thing
with rings polar observations it up and
Aurora of Saturn and then finally as I
mentioned in my first slide we are
actually gonna satyr sample Saturn's
atmosphere every ounce of Cassini's last
efforts will be made in sampling the
atmosphere and trying to understand and
and answer some of the fundamental
issues about the constituents of the
hydrogen helium ratios and things like
that so we'll see let me just quickly
run through this November 30th right
after Thanksgiving this whole thing
starts and this is just to show you that
not only sometimes you get your good and
sometimes you're lucky the longitudinal
coverage of the F rigs is absolutely
phenomenal we're going to get the whole
planet covered with the F ring timeline
of 20 orbits April 22nd is our first
target of flyby this would last targeted
flyby and this is the one from Titan
that's gonna push us in so I'm going to
try to not hit the Go button and show
his Titan it's gonna come in from over
here here's the F F ring final death
ring orbit we're gonna come out back
around and then here comes Titan and
watch what happens to this orbit boom it
does it's it's it's about a couple of
thousand kilometers so it's pretty close
but now rather than going outside and we
go and that's that's going to happen for
22 times and so there's there's that and
I will show you 22 more April 23rd the
grand finale begins and we have a lot of
Titan flybys pushing us around I won't
show you a whole lot of those but the
first dive through the gap and here's
our longitudinal out coverage with the
proximal is again it's almost a perfect
grid all the way around the planet
absolutely phenomenal first dive through
the gap is on April 26th and then Sempra
Timber 11th our last
flyby of Titan and I mentioned that
before we call it t 292 it's so distant
flyby about a hundred thousand
kilometers
but it doesn't take much to push us in
to an impacting trajectory in September
15 boom we're in the end of mission and
in a very spectacular setup a set of
Investigations at Saturn so I want to
share a cartoon with you this we we at
the flat team like to pass around
hey Cassini I hear you're retiring how
about that graps do you want to
celebrate maybe lunch with me and my
moons how about that yeah I'm just gonna
go barreling straight into your
atmosphere learning as much as I can
before I'm crushed to death and vaporize
just spectacular whirling Inferno
beneath your mysterious stormy clouds so
you can imagine Saturn's reaction to
that it's the same it's the same one
that we all have maybe you all have when
you see that we're gonna burn this thing
up you think about that for a little bit
and hopefully what I just told you you
might come to agree with all of us that
it's it's too bad it was a wonderful
machine it's a bit incredible discovery
machine but it's awesome
okay I think we will be happy to
entertain any questions you might have
and if you do have a question and we
appreciate you going up to the
microphone thank you for a really
awesome presentation so I believe that
the Juno mission is using highly
elliptical orbits to explore the
internal structure of Jupiter and I
assume you're you mentioned that you're
going to be probing the magnetic and
gravitational fields of Saturn so my
question is Jupiter they expect to
confirm the existence of metallic
hydrogen inside of Jupiter is Saturn
have enough gravitational pressure to do
to form metallic hydrogen do you believe
yes Saturn certainly has enough pressure
inside to form metallic hydrogen we're
wondering if we can maybe also detect
that boundary inside of Saturn just want
to point out one difference between Juno
and Cassini Juno is in a polar orbit
basically going over the poles Cassini
were only tipped at 63 degrees and
that's basically our optimum orbit to
keep the Peary apps from precessing and
pointing us prematurely into the ring so
very similar complementary science for
the two missions probing the interiors
of two gas giants and then comparing the
results thank you thank you for the
great presentation I wanted to ask about
contingencies during this final year
you're on a risky pathway and if
something were to happen to the
spacecraft on one of these passes
through the Rings do what do you expect
to become of the rest of the mission is
there a chance that it can still have
its crash into Saturn or what yeah
one of the things that's pretty amazing
about this trajectory is once we've
flown by they let that final Titan fly
by if we lose the spacecraft it's still
going in it's if we in as a matter of
fact after t125 we require which is the
penultimate Titan flyby and very minimal
trajectory maintenance yeah we're all
essentially on a ballistic trajectory to
our to our entry now that being said
we're still gonna try to if there are
we've worked contingencies in case we
find the dust is higher than we want
we're gonna we can hide behind the
high-gain antenna if the atmosphere is
thicker than we would like although some
of the scientists think that's just
great we can move ourselves out a little
bit so we have worked a lot of
contingency plans to make sure the
mission is that successful as possible
but if we are damaged we're still will
be able to keep our promise to Enceladus
tighten the atmosphere shrinks and
that's a possibility we also have a plan
we could go a little bit lower because
we want to dip our toe for sure in that
atmosphere of Saturn hi this is more of
a question about the capability of the
spacecraft so I understand that the
decision to deorbit it is quite final
but would it ever have been possible to
attempt you know is there sufficient
Delta V in the tanks to attempt a rocky
or icy moon like smaller moon landing
like a Genki near style you know landing
and use the low gain antenna send
another spacecraft later and have a
passive station sitting in orbit around
Saturn oh they're being afraid well that
could have been in that set of scenarios
there may have been a landing scenario
that we didn't work but now there
absolutely is not when we design the
Solstice mission we designed it and you
you don't want to end a mission with a
full tank in fact you want to end the
mission with a completely empty tank and
right now we are almost completely empty
so that the possibility of a controlled
landing on anything would be absolutely
out of the question again those are
things most of the controlled landings
we see are really more like controlled
crashes there are low-speed crashes and
so really the realist the realistic
opportunity to create a beacon and I
think he wanted to sign something like
Huygens that actually was built to
broadcast up and but unfortunately it
was on batteries didn't that was that
but now it's like you said the decisions
made and we have spent all our
propellant doing what we've been doing
thanks for the question thank you both
for that presentation is excellent you
noted earlier you're concerned over
contaminating the environments of
Enceladus and Titan how were you able to
prevent that when you landed Oregons
probe on the surface of Titan good
question I think the key difference
between those is that Cassini is powered
by these radioisotope thermoelectric
generators with plutonium on board and
so to access the ocean on Enceladus
you'd probably have to melt through some
ice and with the heat from that
plutonium that might be a possibility
the Huygens probe had batteries that had
some small are hu heaters and also when
we landed on Titan we didn't know about
the methane lakes we didn't know that
Titan had also had a global ocean we
didn't know about Enceladus so a lot of
things like his role said Cassini is
kind of a victim of her own discoveries
Jessie thank you well absolutely
absolutely sir per presentations of
course a quick questions what's the
cause of the highlights that we see here
at 12 o'clock and 6 o'clock on the
outermost rings excellent question what
is the cause of those bright spots it
turns out that those spots are actually
you can think of somewhat pulled in
closer to the Sun and so it's sort of a
phase angle effect if you can think of
it that way the the answer are further
away from the Sun than the points at the
north and the south and so they are
brighter as many things brighten as you
get toward that very low phase angle or
that distance between the Sun and your
target is small good question though
good catch to start thank you for a
wonderful presentation I've really
enjoyed it
knowing what we know now about Saturn
what's next and when do we get to go
but well there's a proposal cycle
underway now within this I called new
frontiers and there's a fixed list of
missions for new frontiers one of those
is a Saturn probe much as we had a probe
into Galileo's atmosphere we'd like to
send a probe into Saturn's atmosphere in
particular to measure the noble gases
that you can't really measure any other
way and there are a host of other things
you could do with the probe there also
now two targets that were added to the
list for new frontiers those targets are
Enceladus and Titan basically these new
ocean worlds unveiled by Cassini and so
there are missions to go to fly through
the plumes of Enceladus with more
capable instruments to perhaps look for
those amino and fatty acids missions to
maybe land something in one of those
seas on Titan and make measurements
there so there's a whole host of
proposals there's probably 30 or 40
who-knows-how-many NASA will get
sometime next spring and then they'll
get to pick one of those missions so we
might go back as early but it still is a
long trip you're talking about maybe a
launch in the mid 2020s you know 25 26
and then maybe a decade or so to get
back to Saturn it's not a quick trip to
get there I can't wait thank you and
don't forget Uranus and Neptune I mean
they're out there too and it would be
great to send a flagship mission like
Cassini on out to one of the ice giants
Uranus or Neptune though we just had
tantalizing glimpses with Voyager and to
go back to one of those places for a
future flagship maybe after Europa maybe
a flagship to Uranus or Neptune thank
you so much
I'll jump in for one more question how
long does it take for an image to get
from Cassini to earth-like to get the
data here and my iPhone I think has 8
megapixels
what's Cassini have it's black and white
okay we we colorize our images with
filters and it takes anywhere from an
hour to 90 minutes for the image to get
from Cassini here to to the earth
megapixel image - well they make a pixel
out let's see we do a hundred and forty
kilobits per second so that's so take 10
seconds or so roughly let's take this
say 20 counting overhead you get an
image down here once it starts but
Saturn is an hour and a half flight time
away so when we start when Cassini
starts to send a signal her bits don't
get to the ground for an hour and a half
an hour and a half yeah gotcha
and so when we want a signal you know
send something to Cassini and have it
answer we have to wait anywhere from two
to three hours Wow
that was really great thank you Cassini
has to be very smart you know she has to
basically have commands on board to keep
keep her going typically for 10 weeks at
a time we're at a point where to look
when to send data back and so very very
smart spacecraft actually speaking of
photos I was wondering what's the plan
for in the grand finale photo was like
and what are you expecting to see if you
expect me to take photos are expecting
to see maybe some resolving some
individual clumps of ice in the Rings
since you're going so close or looking
at clouds of Saturn because the
periapsis gonna be so close all right
and you guys expecting to take a lot of
photos from this mission well be taking
a lot of photos of both the Rings and
the planet ring particles on average or
millimeters to centimeters in size even
if they were tens of meters we still
couldn't resolve an individual ring
particle but we certainly could resolve
the structure that we see in the Rings
at much higher resolution SOAs or else
it is on the dark side of the Rings this
is a chance to look at that
resolution but on the lighted side of
the Rings radar of the Rings as well
also we'll get close-up views of the of
the planet of the poles of the
atmosphere itself I think that the
surprises might be the questions we
don't know yet no to ask when we look at
those pictures whereas the Rings or the
planet what might we see also we have a
detector that some of those tiny ring
particles from the main rings charge up
and they field lines then we'll go into
one of our sensors the cosmic dust
analyzer and we'll get for the first
time the direct composition of the Rings
we know they're water ice but we don't
know if the non icy component is
silicates iron Dolan's we don't know
what it is so we'll get the answers for
that for sure for the first time as we
enter the atmosphere everything is going
to be focused on atmospheric
construction and constituents the
spectrometers the fields and particles
there be pointing at the atmosphere
unfortunate that means the camera is
going to be pointing someplace else and
furthermore in order to play all that
data back as fast as we can we have had
to narrow down the bandwidth and
megapixels of megapixel we could get 10
or 20 mass spectrometer packets down for
one one image so the cameras not even
going to be recorded and sent down
during those final seconds thank you
you said in response to an earlier
question that you're getting pictures in
black and white and then you're coloring
them with filters how does that work are
you choosing all red you know we our
cameras have to filter wheels you know
essentially you take and take a green
blue and magenta filter up not magenta
but in green sigh well whatever the
three colors you pick and colorize them
right
it has infrared filters that pure tenets
rate the haze and so each of these
filter wheels you actually rotate that
filter into the image path and take an
image then rotate another filter take
another image and they're combined and
colorized on the ground so the colors
you end up with represent like you're
actually looking at or is it they can or
they can represent some of the false
colors that you've seen like the red
hurricanes and things like that that
accentuate levels of elevation or if Kim
constituents a lot of the pictures
you've seen more unnatural but some of
the others were false color to highlight
whatever be ur logical or chemical you
know I have you trying to look at but
you can't get true color you take those
filters and add them together in
different ways and you get the true
color that you would see with your eyes
and those in those pictures thank you hi
thank you for your presentations I have
two questions here I want to ask first
is that a you guys said um the Cassini
satellite
I mean the Cassini drones were props
whatever is a farthest from the solar
system we has ever gone what I said was
that the Huygens probe landing on the
surface of Titan is the furthest we've
landed a probe on the surface but the
furthest spacecraft now away from the
Sun would be the Voyager spacecraft
they're well past the the orbits of
Neptune Pluto there on out even one of
them into the interstellar wind so light
time there a day and a half for a signal
to get from the probe to earth they're
way out there I see and the other
question I have is that um I ever
remember correctly Saturn has five big
moons correct and so why do you only
land on two two of those moons
well Titan is the very biggest moon and
it's the only moon in our app and our
solar system with a thick atmosphere and
it was the one that had the most
questions and puzzles about it so he we
really had the weight you know on
Cassini to carry just a single probe and
so it was easiest to land on Titan you
could land with the parachute you didn't
need rockets or anything fancy and we
wanted to see what that surface looked
like so if we go back we could carry
probes they could land on multiple moons
and look at those as well oh okay so so
you mean that you choose the moons you
one-line land before right we chose
Titan before Cassini even launched we
had chosen Titan
okay I see thank you thank you for the
very amazing talk I had a question on a
radio occultation for the three
different frequency centers that you
have available in the spacecraft can you
characterize a little bit on ring
particles that are smaller than the
shortest wavelength and larger than the
longer wavelengths and the diffraction
patterns and how we would be able to
ascertain the particle population right
the three wavelengths of the radio
science are very diagnostic in helping
us understand the particle size
distribution of the ring particles and
what we found and in looking at those is
they're pretty much seeing all of the
particles that in that particular size
range for that so they do a good job at
ka X band and s band and looking through
the Rings and sometimes the s-pen signal
was blocked out first because the Rings
are so optically thick and how does the
diffraction or dispersion occur on
particles that are outside those
wavelength correlations well the radio
science actually there's a fairly large
field of view and so it's integrated
particles all the way across that field
of view and sometimes we see diffraction
patterns that tell us that the ring
particles are lining up and are
structured in a certain way forming
these things we call self gravity wakes
we can actually do some work to detect
those in radio science as well if you
want more detailed answers I can I can
give those if you want to come up
afterwards thank you so this is more of
an engineering than a science question
but with all these precise orbital
maneuvers how do you know your position
accurately enough to perform these
maneuvers because you can't exactly open
Google Maps and get your cheap wings I
got a brag a little bit because JPL is
an absolute center of excellence for for
navigation what we do a couple of
different things first of all we track
the spacecraft very carefully we use
Doppler and ranging to measure its
velocity and distance very precisely we
fit that to an orbit
at the same time we're solving for all
the f emeriti x' essentially the
positional points of all the satellites
and saturn and that's a daily process as
a matter of fact we're gonna do a very
tiny otm tonight over trim maneuver
tonight based on latest observations
because we move
you know it's we're moving a kilometer
or maybe a few hundred meters just being
pushed around by our own shenanigans as
well as as smaller forces and so we're
constantly tracking the spacecraft and
over the decades we've you know we've
had we've hit comets I got to say that
the navigation at at Saturn is one of
the triumphs of modern interplanetary
navigation because of the precision that
we're able to to do this you could do
the same thing with much coarser
measurements but you have to be carrying
tremendous amounts of propellant because
every time you miss you got to fix it to
get back on track so now I'd be happy to
share a paper with your - we've got a
lot of papers about this and one of the
comments were the navigation is so good
it's allowed us to go closer and closer
and closer to these targets until we
came within just 50 kilometers of the
South Pole of Enceladus and in fact our
closest flyby was 25 kilometers but it
just wasn't under the pole so we have
just gotten so good we can go close know
where we're going to hit and we don't
miss thanks
I have some online questions here just
want to go through a couple of those a
question from Titan 82 wants to know
what is the temperature of the surface
subsurface ocean of Enceladus well if
it's true that we have hydrothermal
vents it might be as high as close to a
boiling point around those subsurface
vents but clearly if the water is a
liquid even even though it's under a
little bit of pressure and perhaps with
some ammonia it must be very close you
know what must be above the freezing
point of water so we know that that
otherwise the ocean wouldn't be a liquid
the next question is well Cassini be
able to photograph the vertical ring
structures as it passes through the ring
plane that's a great question
unfortunately the answer is no we can't
photograph these vertical structures
very well because there aren't they
aren't very very big we don't think
we'll have the resolution to resolve
something that's a kilometer or or less
and we don't think there's vertical
structure in the C ring and D ring where
we'll get the very closest to the ring
so I'm sure we'll be looking and in fact
we have looked as we've gone through the
the ring plane crossings I don't think
we'll have the resolution to be able to
do that and then a set if we really want
to look for shadows which is a really
great way to look for structure during
this point in the mission there'll be no
shadows cast by the ring particles we're
not an extra knock so okay are there any
other questions okay if not thank you
very much
you
