[NASA radio]
"Project Manager on FSO chord...
maybe a trickle of telemetry left, but
you just heard the signal from the spacecraft is gone and within the next 45 seconds so will be the spacecraft.
I hope you're all as deeply proud of this amazing accomplishment.
Congratulations to you all. This has been an incredible mission, an incredible spacecraft, and you're all an incredible team.
I'm gonna call this the end of mission...
...project manager off the net."
[applause]
The Cassini-Huygens spacecraft spent more than 10 years
studying the crown jewel of our solar system.
With its massive size, beautifully adorned rings, and countless moons offering more data than we could have ever imagined.
Cassini's fate has been eternally sealed inside the ringed gas giant,
yet we continue to learn more about the second largest planet of our solar system.
Today, we'll discuss what we know about Saturn and explore some of the discoveries uncovered by the Cassini spacecraft.
Saturn formed about 4.5 billion years ago when gravity pulled in leftover gas and dust from the birth of our Sun.
Orbiting 1.4 billion km from the Sun, Saturn is the most distant planet visible to the unaided eye,
and in fact was the last planet known since antiquity.
The remaining planets of the outer solar system have discoverers with Neptune being the first planet discovered solely by mathematics.
The oldest written records of Saturn date back to the Assyrians and 700 BCE.
These Babylonian astronomers named it "Star of Ninib".
Around 400 BCE, Greek astronomers also observed Saturn, but they didn't yet realize it was a planet.
Believing it was a star that wandered across the night sky, the ancient Greeks named it Kronos,
the personification of time, leader of the mighty Titans and Zeus's own father.
The ancient Romans later adopted the name of Saturnus, which was Kronos' Roman counterpart.
More than 2,000 years passed before the invention of the telescope
allowed Galileo Galilei to observe Saturn's rings,
but he mistook them for a triple planet.
In 1655, Christiaan Huygens correctly discovered Saturn's rings and its largest moon Titan.
Today, we know that Titan is the second largest moon in the solar system, second only to Jupiter's Ganymede.
In all Saturn has 53 confirmed moons each unique and fascinating worlds in their own right.
A Saturnian year is agonizingly long, taking 29 earth years to complete one revolution around the Sun.
One day on Saturn is only about 10.5 hours; however,
it remains difficult for us to determine a precise time due to the lack of a solid surface.
This incredibly fast rotation causes Saturn to have a shape of an oblate spheroid.
Centrifugal forces literally stretch the planet at the equator
resulting in a radius 10% wider than its polar radius.
Interestingly, the planet closest to a perfect sphere in our solar system is Venus,
due to its incredibly slow rotation where one day is equal to almost 117 days on earth!
With an average radius about 9x that of Earth, Saturn is truly a massive planet
that must be an incredible sight to see in person.
If you include Saturn's rings that extend up to 282,000 km, then it would cover
about two-thirds the distance between the Earth and the moon!
At five hundred and sixty eight septillion kilograms,
Saturn's mass is just over 95 Earth's,
and it's volume is even more impressive at about 763 Earth's.
Although Saturn is incredibly massive. It's mean density is only 0.687 g/cm3.
Which is about 30% less than water and 8x less dense than the Earth at 5.52 g/cm3.
Most of Saturn's volume is composed of hydrogen and helium with the remaining volume consisting of
methane, ammonia, hydrogen deuteride, and ethane.
It's believed that Saturn has a solid core composed of iron-nickel and rock.
Surrounding the core is a thick layer of liquid metallic hydrogen.
This is followed by a layer of liquid helium-saturated molecular hydrogen
that gradually transitions to a gas as pressure decreases with increasing distance away from the core.
Electrical current within the metallic hydrogen layer is thought to give rise to Saturn's planetary magnetic field.
Although weaker than Earth's magnetic field, Saturn's massive size gives it a magnetic moment 580 times that of Earth
Saturn's interior is 2x hotter than the surface of the Sun,
reaching 11,700 degrees Celsius at its core;
and it radiates two-and-a-half times more energy into space than it receives from the Sun.
Infrared images show the incredible amount of energy as it glows a brilliant red deep inside of Saturn.
This energy drives the weather on Saturn before it eventually escapes into space.
Similar to Jupiter, one mechanism of that heat generation may be through the raining out of helium
droplets deep within Saturn's interior.
As the droplets descend through the lower density hydrogen,
the process releases heat by friction and leave Saturn's outer layers depleted of helium.
These descending droplets may have accumulated into a helium shell surrounding the core.
Saturn is blanketed with a hazy, light brown appearance
due to a mixture of yellow ammonia crystals in the upper atmosphere.
While the lower level clouds appear to consist of either ammonium hydrosulfide or water.
Ultraviolet radiation from the Sun causes methane photolysis in the upper atmosphere
leading to a series of hydrocarbon chemical reactions
with the resulting products being carried down by Eddie's in diffusion.
Like earth Saturn is tilted on its axis by 26.73 degrees whereas Earth is tilted at 23.5 degrees.
This means that Saturn experiences seasons.
Although mostly calm in appearance with a faint banding of clouds visible in the upper atmosphere,
the weather on Saturn is hellish!
Wind speeds can reach 1,800 km/h,
second only to Neptune.
Some of the most destructive weather in the solar system is found at Saturn's poles.
A gigantic storm rages Saturn's South Pole! At 5,000 miles across,
it could nearly swallow the entire earth, and the clouds are 5x higher than the eye wall of hurricanes on earth.
Saturn's North Pole is a six-sided jet stream spanning about 30,000 km across.
The hexagon is a wavy jet stream with a massive rotating storm at the center
packing 500 km/h winds!
The sides of the hexagon are each about 13,800 km long, which is longer than the diameter of the earth.
Studies have shown that hexagon shapes can form
in an area of turbulent flow when liquid was rotated
in a circular tank at different speeds at its center and periphery.
Roughly, every 30 years a global weather event of grand scale occurs.
We were lucky enough to witness one during Cassini's visit to the ringed planet.
Known as the great white spot,
scientists found that water vapor and other materials rise up from 160 km below the cloud tops.
The vapor freezes causing the white appearance we see during the storm.
The last storm wrapped around the entire planet spanning some 300,000 km.
Saturn's rings are undoubtedly the feature that makes it so stunning among all the planets in the solar system.
Although we see them as a disc of light, they're primarily composed of chunks of ice and rock.
The reflective nature of ice is the reason they're so stunningly visible to us on earth.
Most of the chunks are tiny, but some are the size of a house and a few are as large as mountains.
The nature of Saturn's rings were not understood until 1859 when James Clerk Maxwell
submitted his overwhelmingly convincing predictions.
Maxwell proved that a regular solid ring could not be stable,
while a fluid ring would be forced by wave action to break up into blobs.
Since neither was observed, Maxwell concluded that the rings must be composed of numerous small particles
he called brickbats, each independently orbiting Saturn.
It would be over 100 years later before his predictions were confirmed during the Voyager flybys.
Saturn's ring system extends up to 282,000 km from the planet,
yet the average vertical height is no taller than a two-story building or typically about ten meters.
The rings were named alphabetically in the order of discovery and can be a bit confusing.
Beginning closest to the planet, the main rings are C, B, and A.
The Cassini division is a gap spanning 4,700 km between the B and A rings.
It was named after Giovanni Cassini who first discovered the gap.
In addition, a number of fainter rings have been discovered more recently.
The D ring is exceedingly faint and closest to the planet.
The F ring is a narrow feature just outside the A ring.
Beyond that are two far fainter rings named G And E.
Weird and interesting things occur inside the ring structure.
There are braided rings
ringlets and spokes -- dark features in the rings that form and initially circle the planet
at different rates from that of the surrounding ring material.
Pan and Daphnis are tiny shepherd moons that orbit between the gaps in the rings.
At 30 km wide, Pan is the second most inner moon orbiting in the Encke gap.
Stray particles are collected by Pan as it works to keep the gap open.
This has caused a rather interesting disc shape at its equator as the ring material is deposited on the moon.
Daphnis is much smaller at 8km wide orbiting within the narrow Keeler gap.
Waves can be seen as it interacts with the nearby ring material.
The moon's Janus and Epimetheus proved to be a truly fascinating discovery.
Saturn's inner B ring forms a two to one
orbital resonance with Janus, as the ring orbits twice for every one orbit of Janus.
This image is deceptive as it appears to be tilted away.
However, as a wave propagates away from the resonance the wavelength decreases
creating this illusion.
Every four years Janus and Epimetheus switch places in their orbits, which creates new crests in the waves.
This has provided a glimpse into the past as the waves form a visual orbital history of Janus and Epimetheus.
Density wave theory was successfully applied to this incredible discovery,
which explains the creation of spiral arms within a spiral galaxy like our own Milky Way.
In effect, Cassini witnessed this creation on a much smaller scale.
Perhaps the most exciting discoveries of Saturn are the moons Titan and Enceladus.
We'll talk more about the moons in another episode,
but many now believe that these two moons are the best candidates for finding life beyond Earth.
With Enceladus ejecting geysers of water from a subsurface ocean,
samples are offered for the taking to any spacecraft passing by with the capability of
analyzing collected samples.
I hope we'll be able to visit this incredible system again in the future for many unanswered questions remain.
Until next time my friends, I'm Tex, happy orbiting!
