TEXT ON SCREEN:   NASA's Cassini
spacecraft arrived at Saturn in 2004.
TEXT ON SCREEN: Cassini studied
Saturn and its moons in the
infrared using its
CIRS instrument.
TEXT ON SCREEN: CIRS is an
infrared spectrometer built and
operated by NASA's
Goddard Space Flight Center.
TEXT ON SCREEN: Here are some
of Cassini CIRS' Greatest Hits.
TEXT:  THE GREAT WHITE SPOT
So in 2010, there was a giant
outburst in Saturn's northern
hemisphere.
A giant storm eruption occurred,
and eventually this spread
around to encircle the entire
globe at a latitude width about
the extent of North America.
Imaging first picked it up,
and it was, it was massive.
From north to south it spanned
about nine thousand miles.
CIRS saw temperature increase
like we've never recorded
before.
CIRS, looking with its thermal
infrared eyes, was able to see
two bright beacons of hotspot
temperatures shining about 150
degrees brighter
than the surroundings.
We, all of a sudden we
had these two bright spots.
After a month or two they
merged, which was kind of
curious, and then it
persisted for another two years.
In fact, it persisted longer
than the tropospheric storm.
Typically on Saturn these occur
about every twenty to thirty
years, this is the sixth one
that's been seen since 1876.
And Cassini was lucky enough to
be there at the right place at
the right time to see
this storm eruption.
TEXT:  PAC-MAN MOONS
Mimas and Tethys are two of I
believe the last count was about
sixty-two moons that Saturn has,
and these are examples of these
icy satellites, two of
Saturn's icy satellites.
When you just take images
with Cassini they look normal.
With Mimas it looks like the
Death Star, you know, and then
you superimpose the
thermal maps from CIRS on it.
And when you superimpose the
thermal maps, it looks like
Pac-Man.
Mimas was an example where
we saw very warm temperatures
surrounding a very cold region,
as if it was going to, you know,
chomp it up.
Turns out the explanation
is kind of, is interesting.
The way these are created is due
to their orbital orientation as
they go around Saturn.
They have a leading side, which
is always towards the front of
its motion, and a trailing side.
And the leading side is
intensely bombarded by radiation
from Saturn's magnetosphere.
So the high-energy particle
bombardment is causing this
fluffy surface, this icy, fluffy
surface, to be packed down to a
very hard, solid ice surface,
and you're changing the way now
the surface can heat up and cool
down over the course of a day
for these moons.
When we look at these in
infrared we see a cooler region
on the leading hemisphere, and
a warmer region surrounding it.
And this gives the exact
appearance of these Pac-Man
features that we
so know and love.
TEXT:  ENCELADUS OCEAN
Enceladus is a very
small, icy moon of Saturn.
It's about three
hundred miles in diameter.
It's a moon that we weren't
expecting to see a lot from, and
it's had a huge impact
on the Saturn system.
Previously, we had hints
that this moon may be active
stretching all the way
back to the Voyager mission.
But when Cassini arrived, it was
able to detect curtains of icy
material venting into space.
Then using the CIRS instrument,
we were able to zoom in on the
south pole, and see the south
pole was much warmer than we
expected.
The pattern of temperatures on
Enceladus did not match a simple
inert body absorbing
sunlight and reradiating it.
The question was what
to make of all this.
The community decided it must be
tidal friction, tidal heating,
as Enceladus orbits Saturn.
This tells us that Enceladus is
being heated up by the action of
Saturn's gravity.
Inside Enceladus, we now know
that there's a liquid water
ocean, and it's this ocean which
is venting through these cracks
into space.
Throughout the mission,
we've learned that it has a
subsurface,
liquid-water environment.
And with NASA, when you see
liquid water, it's "Follow the
water," because
that's important for life.
TEXT:   TARGETING TITAN
Titan was one of the
major objectives of Cassini.
We knew from Voyager that
Titan was an organic molecule
paradise, it just was
filled with organic molecules.
But maybe one of the key things
about Cassini was, instead of a
flyby past the Saturn system,
Cassini hung around for thirteen
years.
And during that time, even
though we were orbiting Saturn,
we flew by Titan a
hundred and twenty-five times.
Titan, at visible wavelengths,
looks like as everyone has seen,
a orange-y, hazy moon.
When Cassini was built, we put
on spectrometers that could see
to longer wavelengths, outside
of the eye's visible range.
And so we removed the veil of
this smog, we peeled it back.
Lo and behold, we saw this
amazing, very active surface.
River channels, and dunes,
and we found polar lakes.
And we never saw this before
because we couldn't penetrate
this very opaque,
hazy atmosphere.
TEXT:  A NEW HYDROCARBON
In 2013, we made a fascinating
discovery about Titan's
atmosphere.
We discovered a new molecule,
which hadn't been previously
detected.
And this is called propylene,
and this molecule, on the Earth,
serves a variety of purposes.
In fact, it's one of the raw
ingredients that we use to make
a type of hard rubbery plastic
commonly known as Tupperware,
which we use in our lunchboxes.
And it was really incredible to
find this molecule just floating
around in Titan's atmosphere.
Going all the way back to
the Voyager mission 32 years
earlier, we'd seen a lighter
molecule and a heavier molecule
in the same chemical family.
But there was a gap at a
particular molecular mass, a
particular size of molecule that
we just couldn't see anything
in.
So this discovery, using CIRS,
filled in this puzzle piece,
which had been completely
outstanding for about thirty-two
years.
TEXT:  THE GRAND FINALE
Cassini's Grand Finale is now
underway as we dive repeatedly
over the planet's north pole,
and through the gap between the
planet and its innermost rings.
We're making gravity
measurements and magnetic field
measurements, and this is
information that we didn't get
earlier in the mission so in
many ways it's like having a
whole new spacecraft mission.
Finally, on the very last orbit,
Cassini will go closer to Saturn
and eventually burn up
in its upper atmosphere.
The spacecraft will disintegrate
and become a permanent part of
Saturn.
[ Satellite beeping ]
