Cassini: Epic Journey at Saturn (live public talk)

(upbeat music) – [Narrator] 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 packed
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 and
Italian Space Agencies has revolutionized our
understanding of Saturn, it’s rings, and 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 inner-most ring and the top of Saturn’s
atmosphere during it’s 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 Maze 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 in avionics, then return to
Cassini as the program manager in January 2013. Dr. Linda Spilker is the
Cassini project scientist and the 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 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 grandmothers ever,
Dr. Linda Spilker. (applause) – Thanks Marc, that was
a great introduction. And, as Marc indicated,
Cassini has truly re-written whole textbooks 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 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 Cassini’s sensitive
cameras and detectors to mosaic this back-lit 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 E ring. 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 Enceladus’ 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 onto the
night side of Saturn. So, just one of the
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 were
in a survey for planetary science, we do these
once ever 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, 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. This shows the earth and the
moon to scale and the distance in between them. 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. Here’s an overview of
the Cassini mission. Cassini was launched
from the earth in 1997. We used gravity
assists, two of Venus, one 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 mission. The Equinox Mission where
the sun was shining right on Saturn’s equator
edge onto the rings, and then a seven year
Solstice mission. And norther 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 call the proximal,
so 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 in inclination
and we’re getting ready for out 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 127 flybys of the
giant moon Titan. And Titan is like a
giant rocket engine. Every time we flyby 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
the prime mission, the first four
years we had three. We discovered Enceladus
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 IC 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 final orbits at the end, and Earl
will be talking about those in more detail. This is a Cassini Orbiter
and the Hoygens 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 antenna. 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 Hoygens 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 as 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. 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. I almost feel like I’m
right there looking through Cassini’s eyes and watching
as she collects her data. And I feel very proud to be
a part of this incredible mission. Now, onto some of the science. This is the tiny
moon, Enceladus. Enceladus is only
300 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 micro-meteorite
bombardment. 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 four
tiger stripe fractures, that’s our nickname for
those bluish features there. Alexandria, Baghdad,
Cairo, and Damascus. 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 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 would 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 1,000 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 a composite infrared spectrometer,
the team that I work with, they found that the
Enceladus south pole was hot. It was about 100 degrees hotter
than the rest of Enceladus. And if Enceladus were frozen
solid it was much hotter 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 an auscultation 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 100 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 Enceladus. 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 the goal of
our flybys is actually to fly through this material. And in October we came
within 50 kilometers 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 back-lit 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 that there’s a global
ocean underneath Enceladus’ icy crust and it’s as though
they were frozen sea spray and they contained 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
in their gardens there and this particular Enceladus
is 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 artists concept
of what might be going on. You have the liquid water
ocean underneath the icy 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, they fall back, and
it’s like it’s snowing. If you could stand near a
tiger stripe underneath it you could put out your
hands and it would be like it would be snowing
on Enceladus. Maybe a future vacation
destination, who knows? But some of the tiniest
grains escape into space. And they’re what go on to
form that very beautiful blue E ring 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 E ring particles
are so tiny that they spread throughout the system and
if you turned off Enceladus’ jets it might only take
100 or 200 years until the E ring is gone completely. So that’s sort of a clue,
we see the E ring we know the jets are going
off at Enceladus. This is just an artists 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 what 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 moon, Dione, 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 hydro-thermal vents on
the sea floor of Enceladus. Now, if we look at our own
planet, we have the same kind of hydro-thermal vents on
the sea floor 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
potassium 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 sea, depending on the composition,
there are black smokers as well. 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
hydro-thermal vents. 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 hydro-thermal vents on the sea floor, 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’ve 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’ ocean? Now, another very interesting
moon is Saturn’s moon, Titan. Titan is about 10 times
bigger than Enceladus and, in 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 a
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 it’s atmosphere. And methane is really
the key at Titan. Because, you see, methane
plays the role at Titan that water plays
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’s surface is just right to 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
large enough they actually fall down onto the
surface of Titan. Now, the Hoygens probe was
built specifically to go through the atmosphere, land on
the surface, and reveal the surface for the first time. So this is an artists
concept of the Hoygens probe. You can see it coming in. It was released from
Cassini on December 25, 2004 and entered into the
atmosphere and landed on Titan on January 15 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 Hoygens
probe floated gently down to the surface of Titan,
softly landed on the surface, and returned data for
another half hour. Cassini was the relay so as
the Hoygens probe was floating down Cassini was flying
overhead collecting the data then to send back to the
earth for the Hoygens probe. So really an amazing mission. With Hoygens 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 Hoygens probe to float, at least
for a few minutes. But it turns 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. At 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 Hoygens 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 lake bed. We had a lamp, you can see
the spot for the lamp here to give us an idea of
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 the 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. We found a world that was
remarkably like the earth in so many ways. In fact, there were lakes and
seas at Titans north pole. Lakes of methane. In fact, this lake by
Geomare is about 50% 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
this sea is a typical depth, you’d have 10 times more
hydracarbons 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 the
way back to the earth, our problems would be solved. But there’s just a tremendous
amount of hydracarbons 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. 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’ve even been
an ancient cryovolcano. 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
in 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 there’s some source
of that methane. Clouds, we’ve seen
lots of clouds. This is a colorized cloud. We’ve seen lots of clouds
and weather on Titan. We even saw a rainstorm, a
methane rainstorm on Titan that darkened the surface
and then we watched with time as the surface slowly dried up. Then here’s a view of
the dry river beds. Now, in looking at these
images, what you see here, 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 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 at five microns it
found a bright spot called a specular reflection. If you have sunlight coming
at an angle reflecting off a liquid surface, it comes
out at the same angle, and if Cassini is looking at
that angle you’ll see a bright spot over the lake. If you’ve 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 wanted to say a
little bit about the rings. The rings have very
simple names, A through G. 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 are the A ring, the
Cassini division, which is astronomer that
discovered the 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 there are also additional
rings just shown in the bottom panel. Here’s the inner-most D
ring, it’s very very faint. You’ve got 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 the Phoebe ring
that actually comes in to the Saturn system, as well. Here’s a Cassini view
of the rings of Saturn. They’re made mostly of water
ice and on average they’re only 30 feet thick. So incredibly narrow for
the hundreds of thousands of kilometers 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 that actually orbit in the rings. There’s one that orbits in
the Yankee gap named Daphnis, another one named Pan. These two moons keep
their gaps open. So we 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 and this movie was taken by Cassini. Basically you’re riding 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 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 A ring is bright, and you can just see a
hint of the bright C ring. 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 their lit and
their unlit sides. Now, Cassini also had a
rare opportunity at Equinox. In fact, we just had our
autumn Equinox and 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 edge on to the rings, essentially,
you’ve turned the sunlight off for the rings. And in 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 dark before Saturn’s shadow,
you had to increase the contrast by about
a factor of 60. Here you can see the narrow F
ring, but it’s slightly tilted so it can still catch the
sunlight, even around Equinox. Now, with 30 foot thick rings
what’s unique is you can look for anything that sticks
up above or below the rings. 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 B ring. And it’s stretched out. And low and behold we found
shadows, lots of them. Turns out that the outer
edge of the B ring is held in place by a resonance
with one of Saturn’s moon. 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 they’re hundreds of
them across the B ring. 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 a space station, if you looked
around noon they’d be hard to see against their
sandy background. But if you looked
near dawn or dusk, the equivalent of Equinox,
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, 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 1,200 kilometers long,
10 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 it was discovered in 2013,
it’s 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
and we’re going to keep watching for her through the
end of the Cassini mission. We’re kind of rooting for
her by now ’cause 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. This storm grew so huge it
was a giant vortex and that vortex swirled 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. So this was 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. This 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. 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 use it as an analogy to storms in the
earths atmosphere. 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 there is a large, very hot, feature. And this feature persisted
for a couple of years and has slowly cooled. So a very dynamic
and active Saturn, at least in that time period. Now, Saturn has a very
interesting feature at it’s north pole. Here’s that feature, you’re
looking right down at the north pole of Saturn. That feature is 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 and hour. And, finally, before I
pass it over to Earl, this is a view of
the changing seasons. In fact, Saturn’s shadow
on the rings you can think of as a giant sun dial. And this picture taken back
in April of 2016 you can see that the shadow of
Saturn goes out 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 shorter at Saturn. With that, I’d like to
turn it over to Earl to talk about the grand finale. (applause) – 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 is it always trumps itself. As we keep finding, one year
we announce a sub-surface ocean the next we
announce a global ocean. So it keeps building and
building and building and 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 tell you at
least the potential for that. Before we do that I want just
a little bit of a backup here. I’m going to go to the end. This is September 14, 2017,
it’s about two o’clock in the afternoon here in
Pasadena and Cassini has just wrapped up a 30 hour or
so observing session. The recorders are packed
full of images and fuels and 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’s going to be
receiving all this data, we’re 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 SSR’s,
the solid state records are empty, be about 10 hours,
Cassini’s going to reconfigure for the periapsis
here at Saturn. So we’ve done that 292 times
over the last seven years. Periapsis at Saturn is pretty
routine, but not this one. This one is absolutely unique. Because it’s Cassini’s 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 the 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 it doesn’t put
the data on the recorder, it’s going to put everything
out on the pipe as quick as it can. So the minute you see,
it’s going to start to turn colors here as
Cassini reconfigures. Cassini’s 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 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 Saturn’s atmosphere. But it’s not going
to be very long. At 77,000 miles per hour,
Cassini is going to be going in with it’s antenna
pointing to the earth, but the atmosphere is going
to quickly overpower it’s ability to point. It just doesn’t have
that kind of control. It’s going to push it off
and then we’ll lose com. It essentially will 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 going to be done. So why are you doing that? First thing. Did you guys ask anybody’s
permission to take something that has rewritten science
programs, redirected NASA programs and re-contoured
missions, you’re just going to destroy it? Let me give you, try to
explain why we think that’s a good idea. In order to do that I’ve 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 end. There was no end-game planned. But we got to the
end of that mission, realized we had an
incredibly good spacecraft, lots of propellant, so we
went for another two years. About midway through that
second mission, 2009, geeze, all sub-systems 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 studies done. There’s a lot of opportunities
at this point with all the sub-systems going. We could’ve left Saturn. We could’ve gone off the
Centaur Asteroids and turn ourselves into, re-configured,
re-purposed Cassini as an asteroid mission. We could’ve, believe it or
not, left Saturn and gone to Jupiter, or gone out to
Uranus, or gone out to Neptune. Now, I gotta say this
was a 40 year cruise. So it would’ve
been a long cruise, but look where Voyager is. It was possible. We could’ve gone
back to Jupiter. That actually is an image
we took on our way out and we could’ve gone back
and spent the same set of resources on Jupiter
as we did on Saturn. Uranus is also a possibility. Or more Saturn. Well, 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 pre-biotic
worlds on their own and Cassini’s still
unwrapping this. So it’s really not hard to
figure, “Okay, we gotta stay.” So I’ll jump to the
chase real quick. Nah, we’re not going there. Nah, we’re not going
there, we’re going to stay. But there’s a catch. If you want to stay at
Saturn, there’s some rules. And they are, we call
it planetary protection, but the real essence of this
is you’ve got to protect Saturn’s ocean worlds. Cassini is essentially a
victim of her own discoveries. My apologies to the Oakridge
boys, but 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
could last forever. We are running essentially
at about 72 degrees inside this spacecraft. So going and taking some of
our earth 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’ve got to be careful about what you do about
Titan and Enceladus. So, with that in
mind you’ll say, “How are we going to do that?” We could stay and
go big long orbits, stay way outside the
orbits of Enceladus, way outside orbits of Titan,
but guess where all the science is? It’s down there with
Titan an Enceladus. So, we want to explore
these guys but we want, at the same time,
to remain safe. So we go to the trajectory
designers, got fair bit of propellant, got good
subsystems, what can you guys do for us? We want to be able to stay
inside Saturn’s 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 incredible worlds. So what these guys gave us
was the Solstice mission trajectory. This started in 2010 and this
is a trajectory designer’s masterpiece. A lot of squiggly lines, but
each of those is an orbit and every time that
orbit changes shape, it’s because Titan moved us. As Linda said, we
get essentially a
Saturn orbit insertion velocity change every
time flyby Titan. So we want to go up, you
fly under Titan and it pulls you up. You want to go in,
you go to the right, go to the left. And it can take you
all over this system. So what we did, what the
trajectory designers did, they took these orbits
that stayed very flat in Saturn’s plane. By the way, that’s Saturn
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 and do magnetic fields and to do
the poles and the rings, and as a bonus to all of
that, 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 mission, something we have
never done before. We’re going to flirt with
the outside of the rings and then we’re going to
go diving deep in between Saturn and the rings. And I’ll show you a
little bit more about that just to show off some here. These things are
just phenomenal. The key orbital characteristics
of this final set of orbits, which we call
the F ring approximals, you’ll hear some of the
flight team call them FERPPO, which sounds more like a dog
food than a real acronym. But really the F ring 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 you’ve never seen. 20 of them are going to
be, oops I’ve hit the wrong button, sorry. I hit it again. There we go. 20 of them are going to be
just outside the F ring. This is the
outer-most ring here. Titan is going to be, both
of these essentially run into Titan right out here. 20 of these outside with
great coverage of the poles and the rings, and then
another Titan flyby is going to move us in to the
gap between the inner most D ring and the outer most
edges of Saturn’s atmosphere. 22 of those. The periapsis is going to
be what we call the 2,400 kilometer clear zone between
the, essentially (mumbling). 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 and behind Saturn, almost every one of them
from a view from earth, provides what we call (mumbles). 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, by the way Saturn
has obliged by never, if you recall back
to Linda’s picture, never opening up the rings
more than they are right now. So essentially be passing
these waves right through. It’s an absolutely unique
and spectacular opportunity. This, again, is just to
show a little bit of what happens at the periapses. You can see, you don’t
quite see the F ring on this illustration, but it is right– Oops, I done it again. There we go. We have these rings here,
the F ring is actually coming out right here. We have about an 8,000
kilometer gap there, but there’s extended dust. And if you look at the F
ring, I’m actually more terrified about that than
I am about the gap because of these tendrils that keep
coming off of the F ring. But nevertheless, that’s
where we’re going. And then again you see the
proximity of these periapses here inside the, what
we call the proximals, the grand finale. This is, again, just
kind of showing off, but here is a
flattened out version. These are the rings of Saturn,
here’s the F ring up here, and here is Saturn’s
atmosphere down here. Saturn atmosphere. Saturn doesn’t have a surface,
or if it does it’s way down in there. So what we call the surface
is essentially one bar level. Essentially the
pressure at sea level. So that’s what we’re calling
the surface of Saturn. So here are, graphically,
each of our periapses. So we’re flirting around in
this safe little gap between the F ring dust– I’ve done it again. We’ll get to that. (laughs) Between the the rings here. Incredibly precise navigation
to stay between the dust hazards between the F ring
and the (mumbles) 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. I should point out there are
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 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 slide a couple of times. Imagine you’re sitting
on the prow of Cassini going through. This is seven seconds of
terror every seven days for seven, plus two months. (chuckles) So, Mars has got
their seven minutes, we’ve got seven seconds
every seven weeks. And this is exactly, 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 that. So the flight team, there
are many of them here, we are going to be very busy. So, the science. I love the engineering
of all this, but really, the engineering is all
because of the science. And this is, this is just
some of the unique things. You’ve seen 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. We’ll 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 which one’s 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 very, very intelligent people
on both sides of the case. We think we can help with
some of these measurements. Saturn’s atmosphere and the
inner-most ring particles and the highest resolution
ever ring observations themselves. We went into orbit in 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 in
that picture earlier, Saturn’s cooperating by
providing an incredibly good phase angle at the sun. Also, we’re going
to radar the rings. You saw the radar
images of Titan, we’re going to try to do the
same thing with the rings. Pole observations
and aurora of Saturn. And then, finally, as I
mentioned in my first slide, we are actually going to
sample Saturn’s atmosphere. Every ounce of Cassini’s
last effort will be made in sampling the atmosphere and
trying to understand 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 30, 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 rings is absolutely phenomenal,
we’re going to get the whole planet covered with the F
ring timeline, 20 orbits. April 22 is our
first targeted flyby, last targeted flyby. And this is the one from
Titan’s going to push us in. So I’m going to try to not hit
the go button and show you. Titan’s going to come in from
over here, here’s the F ring, final F ring orbit. We’re going to come out back
around and then here comes Titan and watch what
happens to this orbit. Boom. It’s about a couple
thousand kilometers, so it’s pretty close. But now, rather than
going outside, in we go. And that’s going to
happen for 22 times. And so there’s that and
I won’t show you 22 more. April 23 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
coverage with the proximals. Again, it’s almost a perfect
grid all the way around the planet. Absolutely phenomenal. First dive through the gap
is on April 26 and then September 11 out
last flyby of Titan. And I mentioned that before. We call it T292. It’s a distance flyby,
about 100,000 kilometers, but it doesn’t take much to
push us in to an impacting trajectory. And September 15,
boom, we’re in. The end of mission and the
end of a very spectacular set of investigations, etc. So, I want to share a cartoon
with you that we at the flight team like to pass around. “Hey Cassini, I hear
you’re retiring. “How about that, congrats.
Do you want to celebrate? “Maybe lunch with
me and my moons.” How about that? “Nah, I’m just going to
go barreling straight into “your atmosphere, learning
as much as I can before “I’m crushed to death and
vaporized to spectacular “whirling inferno beneath your
mysterious stormy clouds.” So you can imagine
Saturn’s reaction to that. It’s the same. (laughter) It’s the same one
that we all have, maybe you all have when
you see that we’re going to burn this thing up. You think about that for
a little bit and hopefully what I just told you might
come to agree with all of us that it’s too bad, it’s
a wonderful machine, it’s been an incredible
discovery machine, but it’s awesome. (applause) Okay, I think we’re– We’d be happy to entertain
any questions you might have. And if you do have a question,
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 mentioned that you’re going to be probing the
magnetic and gravitational fields of Saturn. So my question is, at Jupiter
they expect to confirm the existence of metallic
hydrogen inside of Jupiter. Is Saturn having enough
gravitational pressure 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. I just want to point out
one difference between Juno and Cassini, Juno
is in a polar orbit, basically going over the poles,
Cassini we’re only tipped at 63 degrees. And that’s basically our
optimum orbit to keep the periapses from precessing
and putting us prematurely into the rings. 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, what do you expect
to become of the rest of the mission? Is there a chance that it
can still have it’s crash into Saturn? – Yeah. One of the things that’s
pretty amazing about this trajectory, once we’ve flown
by the final Titan flyby, if we lose the spacecraft,
it’s still going in. And as a matter of fact
after T125 we require, which is the
penultimate Titan flyby, very minimal
trajectory maintenance. We’re essentially on a ballistic
trajectory to our entry. Now, that being said, we’re
still going to try to get, we’ve worked contingencies
in case we find the dust is higher than we want, 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 all the
contingency plans to make sure the mission is as
successful as possible, but if we are damaged, we
still will be able to keep our promise to Enceladus and Titan. – In fact, if 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 de-orbit it is quite final, but it would
it ever have been possible to attempt, is there
sufficient delta V in the tanks to attempt a rocky or icy
moon, smaller moon landing like a janky near style
landing, use the low gain antenna, send another spacecraft
later and have a passive station sitting in
orbit around Saturn. – I’m afraid, well
that could’ve 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 designed the solstice
mission we designed it, 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 the possibility of a
controlled landing on anything would be absolutely
out of the question. Again, those sort of things,
most of the controlled landings that we see are
really more like controlled crashes. They’re low speed crashes
and so really the realistic opportunity to create a
beacon, I think you want to design something like Hoygens
that actually was built to broadcast up. But unfortunately it was on
batteries and that was that. But now it’s, like you
said, the decision is made and we have spent all our
propellant doing what we’ve been doing. Thanks for the question. – Thank you both for that
presentation, it was excellent. You noted earlier your
concern over contaminating the environments of
Enceladus and Titan. How were you able to
prevent that when you landed Hoygens probe on the
surface of Titan? – Ah, good question. I think the key difference
between those is that Cassini is powered by these radio
isotope thermo-electric generators with
plutonium on board. And 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. Hoygens probe had batteries
and it has some small RHU heaters. And also, when we landed on
Titan, we didn’t know about the methane lakes, we didn’t
know that Titan also had a global ocean, we didn’t
know about Enceladus. So a lot of things, as Earl
said, Cassini is kind of a victim of her own discoveries. – I see, thank you. – Absolutely superb
presentations, of course. Quick questions, what’s
the cause of the highlights that we see here at 12
o’clock and six o’clock on the outer most 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 ansa 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 really enjoyed it. Knowing what we know now
about Saturn, what’s next? And when do we get to go? – That’s yours. – Well there’s a proposal
cycle underway now within NASA 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 in
the Galileo’s atmosphere, we’d like to send a probe
into Saturn’s atmosphere, in particular to measure the
nobel gases that you can’t really measure any other way. And there are a host of
other things you could do with a probe. There are 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 or 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, ’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. We’ve 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? My iPhone I think has eight
megapixels, what’s Cassini have? – One megapixel, and
it’s black and white. (laughs) 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 the earth. – Whole megapixel image. – The megapixel, let’s see,
we do 140 kilobits per second. So it’d take 10
seconds or so, roughly, let’s say 20 counting overhead
to get an image down here once it starts. But Saturn is an hour and
a half light 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. So when we want to 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. – It just means Cassini
has to be very smart. She has to basically have
commands on board to keep her going typically
for 10 weeks at a time. Where to point, where to
look, when to send data back, and so very smart spacecraft. – Actually, speaking of
photos, I was wondering what’s the plan for the grand
finale photo wise? Like, what are you
expecting to see? If you’re expecting to take
photos or 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 ’cause the periapses are going to be so close? Are you guys expecting
to take a lot of photos from this mission? – We’ll be taking a lot of
photos of both the rings and the planet. Ring particles, on average,
are millimeters to centimeters in size, even if they
were 10s 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. SOIs are also just 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 planet, of the poles of the
atmosphere itself. I think that the surprises
might be the questions that we don’t yet know to ask. When we look at those pictures,
whether it’s 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 the fill bines then will
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, tholens, we don’t know what it is. So we’ll get the answer
for that for sure for the first time. – I might also add that,
as we enter the atmosphere, everything is going to
be focused on atmospheric construction and constituents. The spectrometers, the
fields and particles, they’re going to be
pointing at the atmosphere, unfortunately 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
to narrow down the bandwidth and a megapixel is a megapixel. We could get 10 or 20 mass
spectrometer packets down for one image. So the camera is 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 or do you
know what colors to use? – Our cameras have
two filter wheels. You know, essentially you
can take a green, blue, and magenta, blue, green,
and whatever three colors you pick and
colorize them, right? It has infrared filters
that penetrate 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 what 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 of
chemical constituents. A lot of the pictures
you’ve seen were natural, but some of the others were
false colored to highlight whatever (mumbles) or
chemical item you’re trying to look at. – But you can 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 in
those pictures. – Thank you. – Hi. Thank you for your
presentations. I have two questions
here I want to ask. First is you guys said
that Cassini satellite, I mean the Cassini drone,
whatever, is the farthest in the solar system
that we have ever gone. – Oh no. – No, what I said was that
Hoygens probe landing on the surface on 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
orbits of Neptune, Pluto, they’re on out, even one of
them into the interstellar winds. – Even at light time,
they’re a day and a half for a signal to get from
the probe to Earth. So they’re way out there. – I see and the other
question I have is that, I remember correctly, Saturn
has five big moons, correct? And so why do you only
land on two of those moons? – Titan is the very biggest
moon and it’s the only moon in our solar system
with a thick atmosphere. And it was the one that
had the most questions and puzzles about it. So we really had the weight
on Cassini to carry just a single probe and so it was
easiest to land on Titan. You could land with a 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 that could land on multiple moons and
look at those, as well. – Okay. So you mean that you choose
the moons you will 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 (mumbles). For the three different
frequency centers that you have available on 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 defraction
patterns and how we would be able to ascertain
the particle population. – 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’ve found in
looking at those is they’re pretty much seeing all
of the particles in that particular size range for that. So they do a good job, the
KA, X band, and S band, in looking through the rings. And sometimes the S band
signal is blocked out first because the rings are
so optically thick. – And how does the defraction
or dispersion occur on particles that are
outside those wavelength correlation? – The radio science actually
there’s a fairly large field of view so it’s
integrated particles all the way across that field of view. And sometimes we see defraction
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
answer 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 for all these
precise orbital maneuvers, how do you know you’re
positioned accurately enough to perform these maneuvers? ‘Cause you can’t exactly
open Google Maps and get your GPS, right? – I’ve got to brag a little
bit because JPL is an absolute center of
excellence 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 it’s velocity and distance very precisely. We fit that to an orbit
and at the same time we’re solving for all
the ephemeralities. Essentially the positional
points of all the satellites and Saturn. And that’s a daily process. As a matter of fact, we’re
going to do a very tiny OTM tonight, over trim
maneuver tonight based on latest observations. Because we move, you know,
we’re moving a kilometer or maybe a few hundred
meters just being pushed around by our own shennanigans
as well as smaller forces. So we’re constantly
tracking the spacecraft. And over the decades
we’ve hit comets, I gotta say the navigation
at Saturn is one of the triumphs of modern
navigation because of the precision that
we’re able to do this. You could do the same thing
with much coarser measurements, but you’d have to be carrying
tremendous amounts of propellant. Because every time you miss
you’ve got to fix it to get back on track. So I’d be happy to share
a paper with you, or two, we’ve got a lot of
papers about this. (chuckles) – And one of the comments,
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. 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 Titan82
wants to know what is the temperature of the surface,
sub-surface ocean of Enceladus? Well if it’s true that we
have hydro-thermal vents, it might be as high as
close to boiling point around those sub-surface vents. But clearly if the water is
a liquid, even though it’s under a little bit of
pressure and perhaps with some ammonia, it must be very
close, it must be above the freezing point of water. So we know that, otherwise the
ocean wouldn’t be a liquid. The next question is will
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 they aren’t very big. We don’t think we’ll have
the resolution to resolve something that’s a
kilometer 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 rings. So I’m sure we’ll be looking
and in fact we have looked as we’ve gone through
the ring plane crossings, I don’t think we’ll have
the resolution to be able to do that. And then if we really
wanted 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 in equinox so. Okay, are there any
other questions? Okay, if not, thank
you very much. (applause) One down, one to go. (upbeat music)

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