Thanks to NordVPN for sponsoring today’s
video. The Cassini mission to the Saturn system has
captured the hearts of many people across the world. Not only was it a fantastic feat of engineering,
it was ambitious with its mission objectives, it was a completely successful mission, and
it took some of the most spectacular images of space that we have ever seen. During its 13 years around Saturn, it sent
back an incredible 635 GB of data, from which more than 4,000 science papers have been published. It discovered 6 new moons. It confirmed that icy moons have subsurface
oceans of salty, liquid water which may well be habitable. It landed a probe on Titan. It observed Saturn’s peculiar storms. And during all this time, it travelled in
excess of 7 billion kilometres. In my opinion, and probably in the opinion
of many of you, it was one of the greatest missions of all time. Now, I’ve already covered a lot of the Cassini
mission in other videos, but one thing a lot of you have wanted to see were the images
it captured near its mission’s end, before it entered Saturn’s atmosphere and disintegrated. Some of these final images are fantastic,
although be aware that Cassini is not capable of real-time video capture. Still, they are definitely worth having a
look at. I’m Alex McColgan, and you’re watching
Astrum, and together we will discuss the final images Cassini ever took. The final phase of Cassini’s mission was
named the Grand Finale, where Cassini performed some of the most dangerous manoeuvres of its
whole mission. Mission controllers sent Cassini into an eccentric,
elliptical orbit over the planet’s poles, and daringly, through gaps in the rings. The last few orbits took it closer to the
surface of Saturn than it had ever been before, giving scientists a new view and perspective
of Saturn. The first time lapse we will look at is from
the 8th September 2017, only one week before the end of Cassini’s mission. One of the main focuses of Cassini during
its mission was the moon Enceladus, one of the prime candidates in the solar system to
contain life in a subsurface ocean. Cassini discovered over 100 water plumes erupting
through the moon’s crust from this ocean, water which freezes in the space environment
and has now formed the beautiful E ring around Saturn. This ring is very tenuous, only visible when
backlit by the Sun, and is potentially the bluest naturally occurring object in the solar
system. Here is a great view of Enceladus’ effect
on the densest part of the E ring, you can see the plumes disturbing and replenishing
the ring. Cassini’s final look at Enceladus’ plumes
were captured in this remarkable time lapse taken over a 14-hour period. On the 11th September, Cassini was near the
furthest point of its final orbit and captured this beautiful mosaic in natural light. Visible are the thickest of Saturn’s rings,
D, C, B, A and F, with Saturn’s short shadow being cast over them. Saturn’s northern hemisphere was experiencing
summer during this time, which means that Saturn’s famous hexagon storm is visible
in all its glory. You can also just about notice Saturn’s
subtle bands in natural light. What’s really interesting about this image,
however, is that the nightside of Saturn is dimly illuminated. This is due to light reflecting off the rings,
meaning Saturn’s nights in the hemisphere facing the Sun don’t get that dark. Below the glow of the rings, Saturn is pitch
black. As Cassini began to approach Saturn again
on the 12th of September, it took images of Saturn’s atmosphere near the planet’s
terminator line. Incredibly, because the Sun is low in the
sky here, huge cloud structures can be seen casting shadows that stretch for many kilometres. You may think this is a close-up of Saturn,
but actually we are looking at a scene about 5,500km across. Saturn’s moon Titan could easily fit in
this shot. Cassini was getting closer and closer to Saturn. On the 13th September, it peered one last
time at Daphnis, a shepherd moon keeping the A ring in check. The gravity of Daphnis causes ripples in the
ring, and some of you keen observers will notice ripples in front of the moon, as well
as behind. This is due to the orbital speeds of the rings
and the moon. The inner ring orbits faster than Daphnis,
meaning the ripples overtake the moon, exposing more ring material to the moon’s gravity. On the other hand, the outer ring travels
slower than Daphnis, meaning the ripples lag behind the moon. By the time the ring material reaches Daphnis
on either side again, the ripples have already smoothed out. On the same day, Cassini had one last look
around the Saturn system. It captured a view of Titan, a moon it focused
on heavily during its mission, a remarkable world with a thick nitrogen atmosphere. It also peered at Saturn’s rings, with the
uneven F ring just about visible at the bottom of the image. And as Saturn got bigger, it took one last
look at Enceladus over a 40-minute period before it disappeared from view behind the
limb of Saturn. The final image Cassini ever took was looking
over the region where it would plunge into the atmosphere. It was night-time here, and so Saturn is lit
up by light reflected off the rings. On the final day, photos were not on the science
agenda. As beautiful as they are, they use up a lot
of valuable bandwidth, and scientists wanted to get every bit of data real time before
the spacecraft was destroyed. This was a unique opportunity; we had never
probed Saturn before this. When Cassini first hit the tenuous parts of
Saturn’s atmosphere, it was traveling 123,000km/h. The remnants of Cassini’s fuel were deployed
by its thrusters to keep Cassini’s antenna aimed at Earth. At this point, Cassini was 1,900km above Saturn’s
clouds. A minute later, these thrusters were firing
at maximum capacity to keep Cassini from spinning out of control. Cassini was directly sampling Saturn’s atmosphere,
but this atmosphere was also heating Cassini up. Just 10 seconds later, the thrusters were
overcome, and Cassini began to tumble, cutting off communication with Earth. Cassini’s onboard computers at this point
would have been trying to figure out what was going wrong. Gyroscopes and star trackers would tell the
computer that it is spinning, and it likely would have gone into a safe mode to divert
power in an attempt to right itself. A minute or so later, the spacecraft would
have disintegrated altogether and burned up in Saturn’s atmosphere. As data started arriving 1 and a half hours
later on Earth, this final part of the mission was deemed to be a great success. Cassini recorded data from direct analysis
of Saturn’s atmosphere, its ionosphere, dust particles in the atmosphere, from magnetic
field measurements and perhaps more that has yet to be uncovered from the data. And that’s the amazing thing about the Cassini
mission, it just keeps on giving. Science papers and discoveries are still being
made as the data it collected is being analysed and re-examined. And great news, missions to the Saturn system
do not end here. Titan will be getting a lander, named Dragonfly,
which will actually be a drone powered by a radioisotope thermoelectric generator, and
its mission is to fly around Titan, directly sampling Titan’s surface in various locations. So, there we have it, a look at the legacy
of Cassini, and of its spectacular final images. Did you know that spacecraft use something
known as the Deep Space Network to communicate with mission controllers on Earth? These are giant communication facilities around
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out the link for their YT channel in the description. Thanks for watching! And a big thank you to those of you that support
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