In just a couple of days’ time from the
making of this video, NASA will be crashing its only Saturn orbiter into the planet. As Cassini enters Saturn’s atmosphere, it
will aim its antenna towards Earth, transmitting data about the composition of the atmosphere
in real-time, until the thrusters can no longer keep the probe steady due to the atmospheric
drag. Cassini will then burn up in Saturn’s atmosphere,
ending a 20 year long mission from launch to final descent. This spacecraft has been an absolute trooper,
surviving and performing in the harsh environment of space, and personally I will be sad to
see it go. The legacy of Cassini will be felt for years
to come though, as scientists are able to trawl over the huge amount of data Cassini
has collected during its mission. During this final part of Cassini’s mission
called the Grand Finale, it has been able to approach the planet closer than ever before,
darting in between the rings. But what has it seen? Has this unique perspective shown anything
we’ve never seen before? Well, starting with the moons of Saturn, it
has seen some of the shepherd moons in unprecedented detail. This is a close approach of Atlas, a 40km
wide moon near the outskirts of the A ring. What looks remarkable about this moon is the
lack of impact craters on its apparently smooth surface, making it look absolutely bizarre. Dust from the rings is collecting over the
surface, particularly around the equator of the moon, smoothing it over and giving it
this disk shape. A similar thing happens with the second-innermost
moon of Saturn, Pan. At 30km wide and found in the Encke Gap, any
particles from the rings that stray into the 350km wide path get swept up by Pan. This keeps the Encke gap steady and constant. Daphnis is another shepherd moon, sadly not
seen in quite so much detail. But due to the gap it is located in, its effect
can be seen for hundreds of kilometres. It is only 8km in diameter, and is found in
a very narrow gap in the A ring called the Keeler gap. Its gravity is very weak, but is just enough
to whisk the nearby dust particles as it brushes by. This creates these waves, or ripple effect
in the nearby rings, sometimes even ripping material directly out of the ring, visible
in this little trail here. Not only do these ripples move side to side,
but up and down too as can be seen by the shadows they create. I can only imagine what it would be like to
sit on Daphnis and watch as waves follow its orbital path, with glorious Saturn and its
many other moons in the background. It would be quite the sight to behold. Talking of the rings though, Cassini has been
able to capture some spectacular images. One of my favourites from the Grand Finale
is this one, showcasing the Janus 2:1 spiral density wave. Amazingly, what you’re looking at here is
the result of the same process that creates spiral galaxies, just much more tightly wound. What appears to be many separate rings, is
actually only two spiral arms looping around the planet many times, so every second line
you see in the image belongs to the same spiral arm. This image is part of the B ring, at a position
where the ring orbits twice for every one orbit of Saturn’s moon Janus, causing an
orbital resonance. The photo gives the illusion that the image
is tilted away at the top left, but this isn’t the case. The illusion is caused by the way density
waves propagate from the planet, the wavelength decreasing with the distance from the resonance. And this is where this resonance gets even
more mind-blowing. Janus, the moon that contributes to the resonance,
switches orbital positions every four years with its close neighbour moon, Epimetheus. Every time this switch takes place, the rings
respond, creating a new crest in the waves. NASA says “The distance between any pair
of crests corresponds to four years' worth of the wave propagating downstream from the
resonance, which means the wave seen here encodes many decades' worth of the orbital
history of Janus and Epimetheus. According to this interpretation, the part
of the wave at the very upper-left of this image corresponds to the positions of Janus
and Epimetheus around the time of the Voyager flybys in 1980 and 1981". This encoding reminds me a bit of a tree trunk
encoding how many years it’s been alive by the amount of rings it has. Simply amazing. Apart from some other beautiful and detailed
images of the rings, other interesting sightings have been these little propeller features
dotted around the rings in a number of locations. This image shows both sides of the rings,
the top image shows the illuminated side and the bottom the unlit side. Even though the scale of the image is only
about 500m per pixel, the moonlet might not even be able to be resolved. You might just be able to see some trace of
it in this top image, but what can be seen is that the moonlet is physically connected
to the rings by this band of materials. As I mentioned, this wasn’t the only moonlet
trying to create a gap in the rings. Here is another found right next to the Encke
gap, and here is another and probably the biggest out of all three. None of these moonlets are thought to be bigger
than 2km and probably have the density of a snowball. The last interesting thing Cassini has been
able to image within the rings is extremely small but solid objects which have formed
around the F ring, potentially caused by the perturbations of some of the shepherd moons
around there. They seem to be solid as they have survived
crashing into the F ring a number of times, kicking out dust and particles which sometimes
then even follow their orbit, as can be seen by the haze around them. The objects themselves are not actually visible
due to the dust obscuring the view. Lastly, let’s look at the planet itself. As Saturn’s northern hemisphere is in full
summer at the moment, its remarkable hexagon around the pole is in full view. In the centre of the hexagon is found a permanent
polar vortex with the eye wall of a massive hurricane. Interestingly, the pole seems to be changing
colour with the season, as you can see quite clearly in comparison to 2012 where the pole
appeared quite dark in colour. With the assistance of other wavelengths of
light, other storms are visible and can be seen dotted all over the planet, as well as
bands reminiscent of Jupiter, just not quite so vivid in natural light. Also, because of the proximity of Cassini
to the planet, it is able to get a good look at the planet’s horizon. On the left of the image can be seen a haze
in the stratosphere of the atmosphere that disappears towards the right of the image. When Cassini does enter the atmosphere on
its final approach, it is thought it will not survive to even reach this haze. Because of the composition of Saturn, it is
not expected Cassini will be able to see much more detail of the atmosphere than what you
would find in this image, but what is of particular interest to scientists is what the atmosphere
consists of. And sadly, that will be the last thing Cassini
will ever send back to Earth before burning up in the atmosphere. And there we have it. A final look at Cassini’s grand finale. I would just like to extend my thanks to the
Cassini team that made all of this space exploration and discovery possible. We have seen and learned things that would
have never been possible if it wasn’t for these intelligent and dedicated individuals,
and I can only hope the discoveries will continue as Cassini’s data is further analysed and
also future missions get underway. If you would like to learn more about Cassini,
Saturn and its moons, then check out the playlist I have for them here. Otherwise, if you are new to the channel,
a big welcome to you and I hope you stick around by subscribing so you don’t miss
out on future content. To my subscribers, I would ask that you consider
clicking this bell symbol next to the subscription so you don’t miss out on future uploads. Lastly a big thank you to my continued support
on my patreon page, the list of patreon’s keeps getting longer and I’m so grateful
to you all for helping me make videos in the future. Big shout out this video to Aber who donated
$50! All the best everyone, and I will see you
next time.
The most impressive image for me is the one of the two spiral arms running parallel to each other as they wrap the planet. I wonder how long each arm is...
Also thanks for the new channel. That video was very well done. I'm surprised he only has 30k subs.
I love this channel. Another great video.
The Waves of Daphnis was my favourite part. I mean just look at them. I'd nominate that as one of Cassini's top 5 images.
Imagine sitting on Daphnis, like he said, and watching these huge waves soar beside you. It must be one of the most beautiful sights in the solar system. I reckon one day when space tourism is a thing an observation base will be set up on the north pole for visitors to see it.
I wish I could be Cassini. What a beautiful way to go.
I was going to submit this video myself, but I'm glad I did a search for this. What a great video!